running injury exercises, running injuries, running injury prevention, impact forces, bones, cartilage, muscles, tendons, ligaments
Running injury exercises - myths about running injuries
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Impact forces - and the heavy effect of the fictions they create
Athletes whose sport involves running put enormous strain on their legs. When they sprint across the soccer pitch, career around the cricket field, blaze up and down the basketball court, orienteer their way through a dense forest, run the final leg of a triathlon, or compete in a 10km road race, each footfall hits one of their legs with a force equal to more than twice their body weight. Just as repeated hammering on an apparently impenetrable rock will eventually reduce the stone to dust, the impact loads associated with running can ultimately break down your bones, cartilage, muscles, tendons, and ligaments - unless you develop clever strategies to attenuate the impact forces properly. Stress fractures induced by running have been documented in almost every bone in the human lower extremity and pelvis (Daffner, RH, 'Stress Fractures in Runners,' Journal of the American Medical Association, Vol. 247(7), p. 1039, 1982), and all athletes are familiar with the muscle and connective-tissue pain which can follow strenuous workouts.
Of course, humans have developed two basic strategies to deal with running's impact stresses: (1) their athletic shoes contain midsoles which deform (compress) in response to impact, absorbing and storing some of the impact force as elastic energy, and (2) their internal tissues deform and change position at impact. With each footfall, the arch of the foot flattens, the ankle joint twists and dorsiflexes, the knee undergoes twisting and flexion, and the hip flexes systematically, all actions which 'soak up' impact force and prevent direct trauma to muscles, bones, and other connective tissues.
And now the bad news
Unfortunately, the injury-preventing strategies sometimes produce injury. The cricket player crying from a cramped calf and unchivalrous Achilles tendon is usually having difficulty not because direct, linear forces are coursing along his Achilles strands and calf-muscle fibres but because of the twisting those tissues undergo with each footstrike - twisting which helps to control impact forces but also puts the Achilles under stress. Similarly, the soccer player with painful plantar fasciitis has aggrieved the structures on the bottom of his foot not because of the direct transfer-through of force but because his arch 'bottoms out' with each strike of the turf (an energy-absorbing mechanism) and thus stretches his plantar fascia mercilessly.
Naturally, there is a popular belief that little can be done about the injury problem, and that sportsmen (and of course sportswomen) who run are doing little more than chipping away at their bones, joints, and sinews, setting themselves up for a rheumatic retirement. When I'm at a cocktail party and reveal (reluctantly to be sure) that I run 45 miles per week, the most common response is, 'Isn't that terribly hard on your knees?'
'Yes, it is,' I reply. 'And by the way, did you know that doing lots of ab crunches could trim away your belly fat?' I usually add, trying to maintain a consistently accurate scientific tone to our conversation.
'In earlier lives, they bought expensive shoes and ran four times a week, but their muscles were weak and their legs and knees became bees'-nests of pain'
But note that the idea that exercise wears out the body can often be attributed directly to the Martini-sippers' past experiences with running. In earlier versions of their lives, they bought expensive shoes and ran four times a week, but their muscles were weak and their legs and knees became bees' nests of pain and discontent. Their resulting conclusion, of course, was not that they should have strength-trained seriously before taking up a running sport, but that running and preservation of body were mutually exclusive.
Alas, scientific research is sometimes used to support such fear-mongering. Some well-read exercise antagonists point to (and sometimes even quote from) an article published in a reputable scientific journal in the early 1980s in which weight-bearing, locomotory sports were directly linked with knee break-downs. In that research, eight athletes walked for four hours per day on a concrete floor. After two and a-half years (!), the athletes displayed abnormal changes in their knee-joint cartilage. Specifically, the glycosamino-glycan contents of their knee cartilage were reduced, a change which is often thought to be predictive of osteoarthritis. The overall picture seemed grim! 'Exercise tears down knee cartilage!' shouted the headlines.
Looking a bit sheepish
But before you believe it, bear in mind that the 'athletes' in this study were actually adult sheep, not humans at all (Radin, EL, et al, 'Effect of Prolonged Walking on Concrete on the Knees of Sheep,' Journal of Biomechanics, Vol. 15(7), pp. 487-492, 1982). The study's authors provided no clues as to whether the sheep had engaged in strength training prior to their 2.5 years of death-marching, and a sceptic could reasonably argue that loading forces - and the musculoskeletal responses to those loading forces - might be somewhat different in human knees, compared with what happens in sheep. Although we haven't fallen prey to the popular idea that sports shoes are 'medicine' against injury, we should at least also point out that the sheep in the study were not clad in expensive clodhoppers, but preferred to clatter about on unshod hooves.
However, we've saved the juiciest bit for last. Although the hard-walked sheep had shoddier cartilage, their knee-joint bones had remodelled themselves and were unusually strong! In addition, there was no real evidence that osteoarthritis was present, so the sheep had adapted pretty well to their marathon-a-day schedules.
Similarly, research with rabbits has also failed to link running with the progression of knee osteoarthritis (Videman, T, 'The Effect of Running on the Osteoarthritic Joint: An Experimental Matched Pair Study with Rabbits,' Rheumatol Rehabil, Vol. 21(1), p. 1, 1982).
'The runners did not have a higher incidence of severe knee and hip pain than the swimmers, nor did the runners undergo surgical procedures more often'
Better still, a follow-up study carried out with humans also failed to link locomotory movements on terra firma with long-term leg damage. Former college athletes from seven major US colleges were interviewed by questionnaire; 504 had been cross-country runners, and 287 were swimmers. The follow-up periods ranged from two to 55 years, with a mean of 25 years; the oldest subject was 77 and the youngest 23, with a mean of 57. As it turned out, the runners did not have a higher incidence of severe knee and hip pain, or even moderate discomfort, comp-ared to the swimmers, nor did the runners undergo surgical procedures for the relief of pain more often. In other words, there was no evidence at all to support the idea that running sports 'broke down the knees'.
The researchers also failed to link either running mileage or the number of years spent running with the development of osteoarthritis (Sohn, Roger S and Micheli, Lyle J, 'The Effect of Running on the Pathogenesis of Osteoarthritis of the Hips and Knees,' Clinical Orthopaedics and Related Research, Vol. 198, pp. 106-109, September 1985).
Briefly, an even better study carried out at Stanford University determined that disabling problems in the legs were five times as likely to occur in sedentary individuals, compared to athletes who engaged in running. Shockingly, the Stanford researchers' data ran against the idea that more running meant more injury, finding that running 15 miles per week cut muscular and skeletal problems by 60%, compared with running five miles per week or less (Anderson, O, 'What's the Truth about Running and Bad Knees?' Running Research News, Vol. 11(8), pp. 10-12, October 1995).
The lesson? If you want your legs to fall apart, your best strategy is to do nothing. If you become sedentary, your leg muscles and bones will decline in function at a rather brisk and predictable rate. Despite what you may hear from the chattering classes, banging your bones and joints around a bit ends up protecting them, instead of wearing them down.
Do hard surfaces cause more injuries?
Some other myths are equally indestructible. For example, a common belief is that running on very hard surfaces (like concrete, cold Tarmac, terrazzo, etc) creates a higher risk of injury, compared to running on relatively soft terrain. Scientific research actually provides little support for this view (Feehery, RV Jr, 'The Bio-mechanics of Running on Different Surfaces,' Clin Podiatr Med Surg, Vol. 3(4), pp. 649-659, October 1986). In fact, the ground-reaction forces at the foot and the shock transmitted through the body all the way up to the head when running on different surfaces varies very little as one moves from very soft to very hard surfaces. Many researchers believe (and there is experimental support for the idea) that runners are subconsciously able to adjust the stiffnesses of their legs just prior to footstrike based upon their perceptions of the hardness of a surface. When moving along on hard surfaces, runners create 'soft' legs, and when they travel across soft surfaces they do so with 'stiff' ones. As a result, impact forces on the legs are similar, despite the wide differences in surface hardness.
'All running animals coordinate the actions of the muscles, tendons and ligaments in their legs so that the overall leg behaves like a single, mechanical spring during ground contact'
In an extremely interesting recent study (Ferris, DP, Louie, M, and Farley, CT, 'Running in the Real World: Adjusting Leg Stiffness for Different Surfaces,' Proc R Soc Lond B Biol Sci, Vol. 265 (1400), pp. 989-994, June 7, 1998), researchers at the University of California at Berkeley hypothesised that all running animals coordinate the actions of the muscles, tendons, and ligaments in their legs so that the overall leg behaves like a single, mechanical spring during ground contact. The Berkeley data suggests that the stiffness of this 'leg spring' is somewhat independent of running speed but is highly dependent on running surface, changing dramatically as an animal encounters surfaces of different stiffnesses. If this were not true, peak ground-reaction force and ground contact time (footstrike time) would change dramatically as an animal ran on different surfaces, but instead they remain fairly constant.
Human runners in particular are very good at adjusting their leg stiffness to accommodate changes in surface hardness, which allows them to maintain similar running mechanics (and absorb similar impact forces) on different surfaces. Taking this into account, engineers designing robots have built adjustable leg stiffness into their designs in order to create more mobile robots.
In fascinating parallel work, the Berkeley researchers found that humans tripled their leg-spring stiffness as they moved across a very compliant surface, compared with running across a very stiff surface (Ferris, DP and Farley, CT, 'Interaction of Leg Stiffness and Surfaces Stiffness during Human Hopping,' Journal of Applied Physiology, Vol. 82(1), pp. 15-22, January 1997). As a result, ground-contact time and centre-of-mass vertical displacement remained remarkably constant in spite of a thousand-fold change in running-surface stiffness. In effect, humans move so that the variation of the sum of leg stiffness and surface stiffness is minimised (as surface stiffness increases, leg stiffness decreases and vice-versa), and impact forces vary to only a small degree as running surfaces change.
Before the first step
In fact, in many athletes this regulation in leg stiffness can occur before they even take their first stride on a surface of different stiffness (Ferris, DP, Liang, K, and Farley, CT, 'Runners Adjust Leg Stiffness for Their First Step on a New Running Surface Journal of Biomechanics, Vol. 32(8), pp. 787-794, August 1999). In a fascinating bit of research, six human subjects ran at a speed of three metres per second on a track with two types of rubber surfaces - a compliant 'soft' surface (surface stiffness = 21.3 kN per metre) and a non-compliant 'hard' surface (surface stiffness = 533 kN per metre). Amazingly, the runners completely adjusted leg stiffness for their first step on the new surface as they ran along the track. For example, runners decreased leg stiffness by 29% between the last step on the soft surface and the first step on the hard surface (from 10.7 kN m(-1) to 7.6 kN m(-1), respectively). As a result, stride rate and the vertical displacement of the centre of mass during stance (approximately 7cm) did not change as the transition was made, despite a reduction in running-surface compression from 6cm to less than 0.25cm!
We should mention that, in spite of all the evidence that impact forces vary to only a small degree as a function of running-surface stiffness, there is some evidence that the softest surfaces can in some cases produce the greatest impact forces! In one study, 15 well-trained athletes walked off a platform 27 inches high and landed on either a very compliant mat or a hard surface. In every case, the impact force on the hard surface was lower, compared with the yielding surface. The researchers suggested this hard-surface-produces-soft-landings effect was caused by 'the landing strategy (sic) chosen by the gymnasts.'
In other words, the athletes, knowing their feet were about to collide with a hard surface, made careful musculoskeletal adjustments to minimise ground-reaction force. When they stepped onto the mat, however, they were a bit sloppy in their preparations, knowing that the mat would 'do the work' (of absorbing shock) for them. Mats, of course, can't optimise footstrike forces; they behave according to their own mechanical characteristics. As a result, reaction forces were higher on the soft mats (McNitt-Gray, JL and Yokoi, T, 'The Influence of Surface Characteristics on the Impulse Characteristics of Drop Landings,' Proceedings of the 13th Annual Meeting of the American Society of Biomechanics, August 23-25, Burl-ington, Vermont, pp. 92-93, 1989).
'Today's athletic shoes tend to treat human feet as fragile objects which need lots of cushioning and support. This knocks out an athlete's intrinsic defence mechanisms against impact forces'
Interestingly enough, the athletes reported that impact forces felt the lightest on the compliant mat. In effect, the yielding surface was creating a feeling of comfort - and as a result an illusion of low ground-reaction force. This has suggested to some sports-medicine specialists and human-performance experts that modern athletic shoes have 'gone off on the wrong track'. The basic idea is that today's athletic shoes tend to treat human feet as fragile objects which need lots of cushioning and support; this cushioning creates a feeling of comfort which 'knocks out' an athlete's intrinsic musculoskeletal defence mechanisms against impact forces and perhaps increases the risk of injury (Robbins, Steven E and Gouw, Gerard J, 'Athletic Footwear: Unsafe Due to Perceptual Illusions,' Medicine and Science in Sports and Exercise, Vol. 23(2), pp. 217-224, 1991). Much more research needs to be carried out in this area.
Speaking of running shoes - given what we have said so far about surface stiffness and impact force, you shouldn't be surprised to learn that running-shoe stiffness seems to have little effect on injury rate; indeed, shoe 'hardness' appears to have only a small and sometimes counterintuitive influence on ground-reaction forces. After all, shoes can be viewed as just another surface upon which athletes run. Put athletes in stiff shoes, and they may simply run with more-compliant legs; place them in soft ones, and they stiffen up.
Indeed, research has failed to support the idea that soft, cushioned shoes actually reduce impact forces. For example, in one study in which runners tried out both soft and hard shoes, they showed slower 'rise times' to peak vertical force during footstrike when they wore the softer shoes, but there were no statistically significant differences in maximal vertical forces (Clarke, TE, Frederick, EC, and Cooper, LB, 'Biomechanical Measurement of Running Shoe Cushioning Properties.' In BM Nigg and BA Kerr, Eds., Biomechanical Aspects of Sport Shoes and Playing Surfaces, pp. 25-33, Calgary, AB: University of Calgary). When the foot hits the ground during running, the ground-reaction force actually increases for the first 20 to 50 milliseconds or so of footstrike time; the rate at which the force increases has been speculated to be related to the risk of injury (ie, high loading rates might give the foot less time to respond and therefore spike the likelihood of injury).
The harder the shoes, the slower the loading rates
To keep things confusing, runners in a different investigation actually had slower loading rates with harder shoes, compared to softer ones, and these runners also experienced lower peak vertical impact forces in the harder shoes (!) (Nigg, BM and Bahlsen, HA, 'Influence of Heel Flare and Midsole Construction on Pronation, Supination, and Impact Forces for Heel-Toe Running,' International Journal of Sport Biomechanics, Vol. 4, pp. 205-219, 1988).
Keeping things interesting, a similar study by the same research group revealed no relationship at all between shoe-midsole hardness and force-loading magnitudes (Nigg, BM, et al, 'The Influence of Running Velocity and Midsole Hardness on External Impact Forces in Heel-Toe Running,' Journal of Biomechanics, Vol. 20, pp. 951-959, 1987).
Over the long term, engaging in sports that involve running will help keep your legs strong and free of disability. Over the short term, however, you need to devise ways to avoid the niggling, temporary injuries which beset athletes who run at fairly high rates. Soft surfaces and soft shoes clearly aren't going to protect you, so what's the best way to shield yourself from running-related injuries? Clearly, the best strategy is to carry out regular strength training, especially running-specific strength training. There is in fact good evidence that resistance training will provide you with broad-spectrum 'coverage' against running injuries (Fleck, Steven J and Falkel, Jeff E, 'Value of Resistance Training for the Reduction of Sports Injuries,' Sports Medicine, Vol. 3, pp. 61-68, 1986).
Tennis players and swimmers
Some of this evidence comes from the world of tennis. In one investigation, exercise scientists determined that tennis players who did not include some form of resistance work in their overall training had a higher frequency of 'tennis elbow,' compared to strength-training devotees (Gruchow, W and Pelleiter, D, 'An Epidemiologic Study of Tennis Elbow,' American Journal of Sports Medicine, Vol. 7, pp. 234-238, 1979).
In this same work, 31% of players who suffered from tennis elbow and undertook a preventative resistance-training programme had a recurrence of the malady, while 41% of the players who utilised no strength training had to battle against tennis elbow again.
In a similar vein, swimmers who engage in resistance training experience a significant decrease in shoulder pain (Dominguez, RH, 'Shoulder Pain in Age Group Swimmers'. In Eriksson and Furlong, Eds., Swimming Medicine IV, pp. 105-109, University Park Press, Baltimore, 1978).
In another study, a strength-training programme consisting of exercises to increase muscular strength and endurance of the external rotator muscles of the shoulders resulted in a significant reduction in shoulder pain (Falkel, JE, et al, 'Effect of Resistive Exercise on Shoulder External Rotation Strength and Endurance in Swimmers, Journal of Orthopaedic and Sports Physical Therapy, 1985). The researchers in this investigation determined that swimmers with the poorest shoulder strength had the highest risk of shoulder injury during training.
Four exercises to protect the legs
Similarly, if you run in your sport, it behoves you to carry out regular strength training to further protect your legs from injury. Your sport itself is somewhat protective, of course; the strength training adds on additional 'coverage' against injuries (Fleck, Steven J and Falkel, Jeff E, 'Value of Resistance Training for the Reduction of Sports Injuries,' Sports Medicine, Vol. 3, pp. 61-68, 1986).
Here are four great exercises which help prevent injury to the legs in sports that involve running:
(1) Partial squats:
Stand with your left foot directly under your left shoulder, keeping your left knee just slightly flexed and maintaining relaxed, fairly erect posture. Hold a barbell (initially with no weights attached) so that it rests on the top-back of your shoulders, just behind your neck; you may incline your upper body just slightly forward for balance. Most of your body weight should be directed through the heel to mid-portion of your left foot. Your right leg should be flexed at the knee so that the right foot is not touching the ground at all - your right foot is literally suspended in air (however, you may occasionally need to 'spot-touch' the floor for balance with your trailing leg).
From this position, if you were going to carry out a traditional one-leg squat you would ordinarily bend your left leg at the knee and lower your body until your left knee reached an angle of about 90 degrees between the back of your thigh and your calf (usually at this 90-degree point your thigh would be almost parallel with the ground). However, for the partial squat you should just go down about half-way - so that the angle between the back of your thigh and lower part of the leg is 135 degrees or so. Then, return to the starting position, maintaining upright posture with your trunk. That's one rep!
So far so good - but you have lots more work to do! Continue in the manner described above until you have completed 10 reps (10 partial squats). Then - without resting - descend into the 11th partial squat, but instead of rising back up hold the partial-squat position (ie, the 135-degree posture) for 10 full seconds. We'll call your body alignment during this 10-second period the 'static-hold' position.
After completing 10 seconds in the static-hold position, immediately - without resting - rattle off 10 more reps, maintain the static hold for 10 seconds again, hit 10 more reps, and then hold statically for 10 more seconds. That's one set on one of your legs!
To summarise, a set proceeds as follows (with no recovery at all within the set):
(A) 10 partial squats
(B) 10 seconds of holding your leg and body in the 135-degree, down position
(C) 10 partial squats
(D) 10 seconds of holding
(E) 10 partial squats
(F) 10 seconds of holding
Once you have completed a set with one leg, immediately perform a set with your other leg. Once you can complete a full set on each leg, add 10 pounds to the barbell for your next strengthening session. Eventually, you will get to a resistance with which you will 'fail' during the third 10-second bout of holding within the set, or perhaps earlier (failure means you won't be able to hold the position for the full 10 seconds). When this happens, don't despair - keep utilising that same resistance until you can finish the whole set on each leg, and then add 10 pounds on your next workout.
Partial squats are great for strengthening your legs, and they give you instant feedback about your improvement. If you can complete a full set using a resistance which has never allowed you to finish the set before, you're stronger! With this partial-squat routine, you get better feedback about your gains in strength, compared with the conventional practice of carrying out two to three sets of 12 to 15 reps using submaximal resistance. Another nice feature: one set of partial squats per leg is enough for a workout; you don't have to do more than one set to get really strong.
(2) One-leg squats with lateral hops
To carry out this amazing exercise, stand with your left foot forward and your right foot back, with your feet about one shin-length apart (they should be hip-width apart from side to side). If possible, place the toes of your right foot on a block or step which is six to eight inches high. Most of your weight should be directed through the mid-portion of your left foot. Now, bend your left leg and lower your body until your left knee reaches an angle of 90 degrees between the thigh and the back of the lower part of the leg.
Once your left knee reaches this 90-degree angle, hop laterally with your left foot about six to 10 inches (your right foot must stay in place), hop back to the centre position, and then hop medially (to the right when your left leg is forward) for six to 10 inches, before coming back to the centre position. Once you are back at the centre position, return to the starting position, straightening out your left leg, holding your hands at your sides, and maintaining upright posture with your trunk. That's one rep!
For starters, complete about 10 reps with your left leg and the same number on your right. Rest for a moment, and then hit a second set of 10 reps on each leg. Wait 24 hours, and then apply ice heavily to your quads and glutes. After 48 to 72 hours, you may carry out the exercise again.
For the following routines, use a round wobble board on a wooden floor or firm, carpeted surface.
(3) Balance-board moves
(A) Side-to-side edge taps. Place one foot directly in the middle of the platform, and note that your board is unstable in all directions (planes). Slowly and deliberately touch or 'tap' the lateral edges of the platform to the ground (left edge, right edge, left, right, etc) for about one minute. Maintain full control at all times, avoiding hasty motions of the balance board. If the exercise is too difficult at first, place the toes of your other foot on the ground behind the wobble board for better balance. Once the minute is up, repeat the exercise on the opposite foot.
(B) Front-to-back edge taps. These are just like the side-to-side exercise, except that you are touching the front edge of the balance board to the floor, then the back edge, etc. Do it for a minute on your left foot and then a minute on your right.
(C) Edge circles. Place your left foot in the centre of the wobble board, and then slowly and deliberately touch the edge of the platform to the floor, rotating this 'edge touch' in a clockwise fashion so that an edge of the platform is in contact with the floor at all times. The actual motion must be very slow and controlled to gain full benefit from the exercise and should be performed for one minute without stopping. As before, place the opposite foot on the ground behind you if a full one-leg balance proves too challenging. Once you have rotated for one minute on one foot, change to the other.
(D) Counter-clockwise edge circles. These are the same as the edge circles, except that you are now rolling the edge along in a counter-clockwise direction.
(4) Downhill hops
Running or hopping downhill increases the ground-reaction forces experienced by the foot and leg, compared with running or hopping on level ground (or uphill). Forcing the legs to respond to these higher forces has an overall strengthening effect. Start with a moderate downslope of about 3%, and hop downhill on your right foot for about 20 metres or so, staying relaxed at all times, looking ahead (not down at your right foot), and achieving good springiness with your right ankle. Jog back up, repeat with the left foot, and your first set is complete. Rest for a moment if necessary, and then carry out two more sets. As you get stronger and more coordinated, you can increase your speed of hopping, the length of the downslope, and of course the percentage declination. Don't try for long leaps as you go downhill; you are looking for quick, efficient bounces, minimising energy cost and 'pogo-sticking' your way down the hill (ie, using the elastic energy of your ankles and legs as much as possible).
Owen Anderson
Of course, humans have developed two basic strategies to deal with running's impact stresses: (1) their athletic shoes contain midsoles which deform (compress) in response to impact, absorbing and storing some of the impact force as elastic energy, and (2) their internal tissues deform and change position at impact. With each footfall, the arch of the foot flattens, the ankle joint twists and dorsiflexes, the knee undergoes twisting and flexion, and the hip flexes systematically, all actions which 'soak up' impact force and prevent direct trauma to muscles, bones, and other connective tissues.
And now the bad news
Unfortunately, the injury-preventing strategies sometimes produce injury. The cricket player crying from a cramped calf and unchivalrous Achilles tendon is usually having difficulty not because direct, linear forces are coursing along his Achilles strands and calf-muscle fibres but because of the twisting those tissues undergo with each footstrike - twisting which helps to control impact forces but also puts the Achilles under stress. Similarly, the soccer player with painful plantar fasciitis has aggrieved the structures on the bottom of his foot not because of the direct transfer-through of force but because his arch 'bottoms out' with each strike of the turf (an energy-absorbing mechanism) and thus stretches his plantar fascia mercilessly.
Naturally, there is a popular belief that little can be done about the injury problem, and that sportsmen (and of course sportswomen) who run are doing little more than chipping away at their bones, joints, and sinews, setting themselves up for a rheumatic retirement. When I'm at a cocktail party and reveal (reluctantly to be sure) that I run 45 miles per week, the most common response is, 'Isn't that terribly hard on your knees?'
'Yes, it is,' I reply. 'And by the way, did you know that doing lots of ab crunches could trim away your belly fat?' I usually add, trying to maintain a consistently accurate scientific tone to our conversation.
'In earlier lives, they bought expensive shoes and ran four times a week, but their muscles were weak and their legs and knees became bees'-nests of pain'
But note that the idea that exercise wears out the body can often be attributed directly to the Martini-sippers' past experiences with running. In earlier versions of their lives, they bought expensive shoes and ran four times a week, but their muscles were weak and their legs and knees became bees' nests of pain and discontent. Their resulting conclusion, of course, was not that they should have strength-trained seriously before taking up a running sport, but that running and preservation of body were mutually exclusive.
Alas, scientific research is sometimes used to support such fear-mongering. Some well-read exercise antagonists point to (and sometimes even quote from) an article published in a reputable scientific journal in the early 1980s in which weight-bearing, locomotory sports were directly linked with knee break-downs. In that research, eight athletes walked for four hours per day on a concrete floor. After two and a-half years (!), the athletes displayed abnormal changes in their knee-joint cartilage. Specifically, the glycosamino-glycan contents of their knee cartilage were reduced, a change which is often thought to be predictive of osteoarthritis. The overall picture seemed grim! 'Exercise tears down knee cartilage!' shouted the headlines.
Looking a bit sheepish
But before you believe it, bear in mind that the 'athletes' in this study were actually adult sheep, not humans at all (Radin, EL, et al, 'Effect of Prolonged Walking on Concrete on the Knees of Sheep,' Journal of Biomechanics, Vol. 15(7), pp. 487-492, 1982). The study's authors provided no clues as to whether the sheep had engaged in strength training prior to their 2.5 years of death-marching, and a sceptic could reasonably argue that loading forces - and the musculoskeletal responses to those loading forces - might be somewhat different in human knees, compared with what happens in sheep. Although we haven't fallen prey to the popular idea that sports shoes are 'medicine' against injury, we should at least also point out that the sheep in the study were not clad in expensive clodhoppers, but preferred to clatter about on unshod hooves.
However, we've saved the juiciest bit for last. Although the hard-walked sheep had shoddier cartilage, their knee-joint bones had remodelled themselves and were unusually strong! In addition, there was no real evidence that osteoarthritis was present, so the sheep had adapted pretty well to their marathon-a-day schedules.
Similarly, research with rabbits has also failed to link running with the progression of knee osteoarthritis (Videman, T, 'The Effect of Running on the Osteoarthritic Joint: An Experimental Matched Pair Study with Rabbits,' Rheumatol Rehabil, Vol. 21(1), p. 1, 1982).
'The runners did not have a higher incidence of severe knee and hip pain than the swimmers, nor did the runners undergo surgical procedures more often'
Better still, a follow-up study carried out with humans also failed to link locomotory movements on terra firma with long-term leg damage. Former college athletes from seven major US colleges were interviewed by questionnaire; 504 had been cross-country runners, and 287 were swimmers. The follow-up periods ranged from two to 55 years, with a mean of 25 years; the oldest subject was 77 and the youngest 23, with a mean of 57. As it turned out, the runners did not have a higher incidence of severe knee and hip pain, or even moderate discomfort, comp-ared to the swimmers, nor did the runners undergo surgical procedures for the relief of pain more often. In other words, there was no evidence at all to support the idea that running sports 'broke down the knees'.
The researchers also failed to link either running mileage or the number of years spent running with the development of osteoarthritis (Sohn, Roger S and Micheli, Lyle J, 'The Effect of Running on the Pathogenesis of Osteoarthritis of the Hips and Knees,' Clinical Orthopaedics and Related Research, Vol. 198, pp. 106-109, September 1985).
Briefly, an even better study carried out at Stanford University determined that disabling problems in the legs were five times as likely to occur in sedentary individuals, compared to athletes who engaged in running. Shockingly, the Stanford researchers' data ran against the idea that more running meant more injury, finding that running 15 miles per week cut muscular and skeletal problems by 60%, compared with running five miles per week or less (Anderson, O, 'What's the Truth about Running and Bad Knees?' Running Research News, Vol. 11(8), pp. 10-12, October 1995).
The lesson? If you want your legs to fall apart, your best strategy is to do nothing. If you become sedentary, your leg muscles and bones will decline in function at a rather brisk and predictable rate. Despite what you may hear from the chattering classes, banging your bones and joints around a bit ends up protecting them, instead of wearing them down.
Do hard surfaces cause more injuries?
Some other myths are equally indestructible. For example, a common belief is that running on very hard surfaces (like concrete, cold Tarmac, terrazzo, etc) creates a higher risk of injury, compared to running on relatively soft terrain. Scientific research actually provides little support for this view (Feehery, RV Jr, 'The Bio-mechanics of Running on Different Surfaces,' Clin Podiatr Med Surg, Vol. 3(4), pp. 649-659, October 1986). In fact, the ground-reaction forces at the foot and the shock transmitted through the body all the way up to the head when running on different surfaces varies very little as one moves from very soft to very hard surfaces. Many researchers believe (and there is experimental support for the idea) that runners are subconsciously able to adjust the stiffnesses of their legs just prior to footstrike based upon their perceptions of the hardness of a surface. When moving along on hard surfaces, runners create 'soft' legs, and when they travel across soft surfaces they do so with 'stiff' ones. As a result, impact forces on the legs are similar, despite the wide differences in surface hardness.
'All running animals coordinate the actions of the muscles, tendons and ligaments in their legs so that the overall leg behaves like a single, mechanical spring during ground contact'
In an extremely interesting recent study (Ferris, DP, Louie, M, and Farley, CT, 'Running in the Real World: Adjusting Leg Stiffness for Different Surfaces,' Proc R Soc Lond B Biol Sci, Vol. 265 (1400), pp. 989-994, June 7, 1998), researchers at the University of California at Berkeley hypothesised that all running animals coordinate the actions of the muscles, tendons, and ligaments in their legs so that the overall leg behaves like a single, mechanical spring during ground contact. The Berkeley data suggests that the stiffness of this 'leg spring' is somewhat independent of running speed but is highly dependent on running surface, changing dramatically as an animal encounters surfaces of different stiffnesses. If this were not true, peak ground-reaction force and ground contact time (footstrike time) would change dramatically as an animal ran on different surfaces, but instead they remain fairly constant.
Human runners in particular are very good at adjusting their leg stiffness to accommodate changes in surface hardness, which allows them to maintain similar running mechanics (and absorb similar impact forces) on different surfaces. Taking this into account, engineers designing robots have built adjustable leg stiffness into their designs in order to create more mobile robots.
In fascinating parallel work, the Berkeley researchers found that humans tripled their leg-spring stiffness as they moved across a very compliant surface, compared with running across a very stiff surface (Ferris, DP and Farley, CT, 'Interaction of Leg Stiffness and Surfaces Stiffness during Human Hopping,' Journal of Applied Physiology, Vol. 82(1), pp. 15-22, January 1997). As a result, ground-contact time and centre-of-mass vertical displacement remained remarkably constant in spite of a thousand-fold change in running-surface stiffness. In effect, humans move so that the variation of the sum of leg stiffness and surface stiffness is minimised (as surface stiffness increases, leg stiffness decreases and vice-versa), and impact forces vary to only a small degree as running surfaces change.
Before the first step
In fact, in many athletes this regulation in leg stiffness can occur before they even take their first stride on a surface of different stiffness (Ferris, DP, Liang, K, and Farley, CT, 'Runners Adjust Leg Stiffness for Their First Step on a New Running Surface Journal of Biomechanics, Vol. 32(8), pp. 787-794, August 1999). In a fascinating bit of research, six human subjects ran at a speed of three metres per second on a track with two types of rubber surfaces - a compliant 'soft' surface (surface stiffness = 21.3 kN per metre) and a non-compliant 'hard' surface (surface stiffness = 533 kN per metre). Amazingly, the runners completely adjusted leg stiffness for their first step on the new surface as they ran along the track. For example, runners decreased leg stiffness by 29% between the last step on the soft surface and the first step on the hard surface (from 10.7 kN m(-1) to 7.6 kN m(-1), respectively). As a result, stride rate and the vertical displacement of the centre of mass during stance (approximately 7cm) did not change as the transition was made, despite a reduction in running-surface compression from 6cm to less than 0.25cm!
We should mention that, in spite of all the evidence that impact forces vary to only a small degree as a function of running-surface stiffness, there is some evidence that the softest surfaces can in some cases produce the greatest impact forces! In one study, 15 well-trained athletes walked off a platform 27 inches high and landed on either a very compliant mat or a hard surface. In every case, the impact force on the hard surface was lower, compared with the yielding surface. The researchers suggested this hard-surface-produces-soft-landings effect was caused by 'the landing strategy (sic) chosen by the gymnasts.'
In other words, the athletes, knowing their feet were about to collide with a hard surface, made careful musculoskeletal adjustments to minimise ground-reaction force. When they stepped onto the mat, however, they were a bit sloppy in their preparations, knowing that the mat would 'do the work' (of absorbing shock) for them. Mats, of course, can't optimise footstrike forces; they behave according to their own mechanical characteristics. As a result, reaction forces were higher on the soft mats (McNitt-Gray, JL and Yokoi, T, 'The Influence of Surface Characteristics on the Impulse Characteristics of Drop Landings,' Proceedings of the 13th Annual Meeting of the American Society of Biomechanics, August 23-25, Burl-ington, Vermont, pp. 92-93, 1989).
'Today's athletic shoes tend to treat human feet as fragile objects which need lots of cushioning and support. This knocks out an athlete's intrinsic defence mechanisms against impact forces'
Interestingly enough, the athletes reported that impact forces felt the lightest on the compliant mat. In effect, the yielding surface was creating a feeling of comfort - and as a result an illusion of low ground-reaction force. This has suggested to some sports-medicine specialists and human-performance experts that modern athletic shoes have 'gone off on the wrong track'. The basic idea is that today's athletic shoes tend to treat human feet as fragile objects which need lots of cushioning and support; this cushioning creates a feeling of comfort which 'knocks out' an athlete's intrinsic musculoskeletal defence mechanisms against impact forces and perhaps increases the risk of injury (Robbins, Steven E and Gouw, Gerard J, 'Athletic Footwear: Unsafe Due to Perceptual Illusions,' Medicine and Science in Sports and Exercise, Vol. 23(2), pp. 217-224, 1991). Much more research needs to be carried out in this area.
Speaking of running shoes - given what we have said so far about surface stiffness and impact force, you shouldn't be surprised to learn that running-shoe stiffness seems to have little effect on injury rate; indeed, shoe 'hardness' appears to have only a small and sometimes counterintuitive influence on ground-reaction forces. After all, shoes can be viewed as just another surface upon which athletes run. Put athletes in stiff shoes, and they may simply run with more-compliant legs; place them in soft ones, and they stiffen up.
Indeed, research has failed to support the idea that soft, cushioned shoes actually reduce impact forces. For example, in one study in which runners tried out both soft and hard shoes, they showed slower 'rise times' to peak vertical force during footstrike when they wore the softer shoes, but there were no statistically significant differences in maximal vertical forces (Clarke, TE, Frederick, EC, and Cooper, LB, 'Biomechanical Measurement of Running Shoe Cushioning Properties.' In BM Nigg and BA Kerr, Eds., Biomechanical Aspects of Sport Shoes and Playing Surfaces, pp. 25-33, Calgary, AB: University of Calgary). When the foot hits the ground during running, the ground-reaction force actually increases for the first 20 to 50 milliseconds or so of footstrike time; the rate at which the force increases has been speculated to be related to the risk of injury (ie, high loading rates might give the foot less time to respond and therefore spike the likelihood of injury).
The harder the shoes, the slower the loading rates
To keep things confusing, runners in a different investigation actually had slower loading rates with harder shoes, compared to softer ones, and these runners also experienced lower peak vertical impact forces in the harder shoes (!) (Nigg, BM and Bahlsen, HA, 'Influence of Heel Flare and Midsole Construction on Pronation, Supination, and Impact Forces for Heel-Toe Running,' International Journal of Sport Biomechanics, Vol. 4, pp. 205-219, 1988).
Keeping things interesting, a similar study by the same research group revealed no relationship at all between shoe-midsole hardness and force-loading magnitudes (Nigg, BM, et al, 'The Influence of Running Velocity and Midsole Hardness on External Impact Forces in Heel-Toe Running,' Journal of Biomechanics, Vol. 20, pp. 951-959, 1987).
Over the long term, engaging in sports that involve running will help keep your legs strong and free of disability. Over the short term, however, you need to devise ways to avoid the niggling, temporary injuries which beset athletes who run at fairly high rates. Soft surfaces and soft shoes clearly aren't going to protect you, so what's the best way to shield yourself from running-related injuries? Clearly, the best strategy is to carry out regular strength training, especially running-specific strength training. There is in fact good evidence that resistance training will provide you with broad-spectrum 'coverage' against running injuries (Fleck, Steven J and Falkel, Jeff E, 'Value of Resistance Training for the Reduction of Sports Injuries,' Sports Medicine, Vol. 3, pp. 61-68, 1986).
Tennis players and swimmers
Some of this evidence comes from the world of tennis. In one investigation, exercise scientists determined that tennis players who did not include some form of resistance work in their overall training had a higher frequency of 'tennis elbow,' compared to strength-training devotees (Gruchow, W and Pelleiter, D, 'An Epidemiologic Study of Tennis Elbow,' American Journal of Sports Medicine, Vol. 7, pp. 234-238, 1979).
In this same work, 31% of players who suffered from tennis elbow and undertook a preventative resistance-training programme had a recurrence of the malady, while 41% of the players who utilised no strength training had to battle against tennis elbow again.
In a similar vein, swimmers who engage in resistance training experience a significant decrease in shoulder pain (Dominguez, RH, 'Shoulder Pain in Age Group Swimmers'. In Eriksson and Furlong, Eds., Swimming Medicine IV, pp. 105-109, University Park Press, Baltimore, 1978).
In another study, a strength-training programme consisting of exercises to increase muscular strength and endurance of the external rotator muscles of the shoulders resulted in a significant reduction in shoulder pain (Falkel, JE, et al, 'Effect of Resistive Exercise on Shoulder External Rotation Strength and Endurance in Swimmers, Journal of Orthopaedic and Sports Physical Therapy, 1985). The researchers in this investigation determined that swimmers with the poorest shoulder strength had the highest risk of shoulder injury during training.
Similarly, if you run in your sport, it behoves you to carry out regular strength training to further protect your legs from injury. Your sport itself is somewhat protective, of course; the strength training adds on additional 'coverage' against injuries (Fleck, Steven J and Falkel, Jeff E, 'Value of Resistance Training for the Reduction of Sports Injuries,' Sports Medicine, Vol. 3, pp. 61-68, 1986).
Here are four great exercises which help prevent injury to the legs in sports that involve running:
(1) Partial squats:
Stand with your left foot directly under your left shoulder, keeping your left knee just slightly flexed and maintaining relaxed, fairly erect posture. Hold a barbell (initially with no weights attached) so that it rests on the top-back of your shoulders, just behind your neck; you may incline your upper body just slightly forward for balance. Most of your body weight should be directed through the heel to mid-portion of your left foot. Your right leg should be flexed at the knee so that the right foot is not touching the ground at all - your right foot is literally suspended in air (however, you may occasionally need to 'spot-touch' the floor for balance with your trailing leg).
From this position, if you were going to carry out a traditional one-leg squat you would ordinarily bend your left leg at the knee and lower your body until your left knee reached an angle of about 90 degrees between the back of your thigh and your calf (usually at this 90-degree point your thigh would be almost parallel with the ground). However, for the partial squat you should just go down about half-way - so that the angle between the back of your thigh and lower part of the leg is 135 degrees or so. Then, return to the starting position, maintaining upright posture with your trunk. That's one rep!
So far so good - but you have lots more work to do! Continue in the manner described above until you have completed 10 reps (10 partial squats). Then - without resting - descend into the 11th partial squat, but instead of rising back up hold the partial-squat position (ie, the 135-degree posture) for 10 full seconds. We'll call your body alignment during this 10-second period the 'static-hold' position.
After completing 10 seconds in the static-hold position, immediately - without resting - rattle off 10 more reps, maintain the static hold for 10 seconds again, hit 10 more reps, and then hold statically for 10 more seconds. That's one set on one of your legs!
To summarise, a set proceeds as follows (with no recovery at all within the set):
(A) 10 partial squats
(B) 10 seconds of holding your leg and body in the 135-degree, down position
(C) 10 partial squats
(D) 10 seconds of holding
(E) 10 partial squats
(F) 10 seconds of holding
Once you have completed a set with one leg, immediately perform a set with your other leg. Once you can complete a full set on each leg, add 10 pounds to the barbell for your next strengthening session. Eventually, you will get to a resistance with which you will 'fail' during the third 10-second bout of holding within the set, or perhaps earlier (failure means you won't be able to hold the position for the full 10 seconds). When this happens, don't despair - keep utilising that same resistance until you can finish the whole set on each leg, and then add 10 pounds on your next workout.
Partial squats are great for strengthening your legs, and they give you instant feedback about your improvement. If you can complete a full set using a resistance which has never allowed you to finish the set before, you're stronger! With this partial-squat routine, you get better feedback about your gains in strength, compared with the conventional practice of carrying out two to three sets of 12 to 15 reps using submaximal resistance. Another nice feature: one set of partial squats per leg is enough for a workout; you don't have to do more than one set to get really strong.
(2) One-leg squats with lateral hops
To carry out this amazing exercise, stand with your left foot forward and your right foot back, with your feet about one shin-length apart (they should be hip-width apart from side to side). If possible, place the toes of your right foot on a block or step which is six to eight inches high. Most of your weight should be directed through the mid-portion of your left foot. Now, bend your left leg and lower your body until your left knee reaches an angle of 90 degrees between the thigh and the back of the lower part of the leg.
Once your left knee reaches this 90-degree angle, hop laterally with your left foot about six to 10 inches (your right foot must stay in place), hop back to the centre position, and then hop medially (to the right when your left leg is forward) for six to 10 inches, before coming back to the centre position. Once you are back at the centre position, return to the starting position, straightening out your left leg, holding your hands at your sides, and maintaining upright posture with your trunk. That's one rep!
For starters, complete about 10 reps with your left leg and the same number on your right. Rest for a moment, and then hit a second set of 10 reps on each leg. Wait 24 hours, and then apply ice heavily to your quads and glutes. After 48 to 72 hours, you may carry out the exercise again.
For the following routines, use a round wobble board on a wooden floor or firm, carpeted surface.
(3) Balance-board moves
(A) Side-to-side edge taps. Place one foot directly in the middle of the platform, and note that your board is unstable in all directions (planes). Slowly and deliberately touch or 'tap' the lateral edges of the platform to the ground (left edge, right edge, left, right, etc) for about one minute. Maintain full control at all times, avoiding hasty motions of the balance board. If the exercise is too difficult at first, place the toes of your other foot on the ground behind the wobble board for better balance. Once the minute is up, repeat the exercise on the opposite foot.
(B) Front-to-back edge taps. These are just like the side-to-side exercise, except that you are touching the front edge of the balance board to the floor, then the back edge, etc. Do it for a minute on your left foot and then a minute on your right.
(C) Edge circles. Place your left foot in the centre of the wobble board, and then slowly and deliberately touch the edge of the platform to the floor, rotating this 'edge touch' in a clockwise fashion so that an edge of the platform is in contact with the floor at all times. The actual motion must be very slow and controlled to gain full benefit from the exercise and should be performed for one minute without stopping. As before, place the opposite foot on the ground behind you if a full one-leg balance proves too challenging. Once you have rotated for one minute on one foot, change to the other.
(D) Counter-clockwise edge circles. These are the same as the edge circles, except that you are now rolling the edge along in a counter-clockwise direction.
(4) Downhill hops
Running or hopping downhill increases the ground-reaction forces experienced by the foot and leg, compared with running or hopping on level ground (or uphill). Forcing the legs to respond to these higher forces has an overall strengthening effect. Start with a moderate downslope of about 3%, and hop downhill on your right foot for about 20 metres or so, staying relaxed at all times, looking ahead (not down at your right foot), and achieving good springiness with your right ankle. Jog back up, repeat with the left foot, and your first set is complete. Rest for a moment if necessary, and then carry out two more sets. As you get stronger and more coordinated, you can increase your speed of hopping, the length of the downslope, and of course the percentage declination. Don't try for long leaps as you go downhill; you are looking for quick, efficient bounces, minimising energy cost and 'pogo-sticking' your way down the hill (ie, using the elastic energy of your ankles and legs as much as possible).
Owen Anderson
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