Nearly 50% of sports injuries occur at the tendon(1). That tough yet semi-elastic piece of connective tissue that connects muscles to bones still seems to be the weak link in athletic movement. As Alicia Filley reviews, we’ve come a long way from thinking of it as a purely inflammatory problem. We now know that there... MORE
Skeletal health: boning up on vibration and resistance training
Andrew Hamilton discusses the merits or otherwise of training interventions to improve bone health.
Low-impact sports such as swimming and cycling are extremely effective for building cardiovascular health and muscular strength. Moreover, the smooth spinning action of pedaling and the low-gravity environment of the water is comparatively gentle on joints, tendons and ligaments, which means even the most injury-prone sportsmen and women can train harder and longer into older age without the potential injury risks posed by other sports such as running.
The downside of low impact training
Despite these numerous health benefits however, there’s a downside to this ‘gentle’ aspect of cycling and swimming because when a training program consists of only smooth and impact-free movements, the main bones in the body are not subjected to much stress and loading. This matters because regular loading of the bones is critical for maintaining bone health – in particular, for developing and maintaining bone mineral density (BMD)(1). Building high levels of BMD and keeping them high is important and very desirable as low levels of BMD can be associated with serious health consequences in later life. In particular, low levels of BMD are associated with an increased risk of osteoporosis(2).
Osteoporosis: the silent crippler
Osteoporosis (which quite literally means ‘porous bones’) is often known as the ‘silent crippler’ because it often progresses painlessly and unnoticed, until a bone actually fractures. Although any bone can be affected, fractures of the hip and spine are particularly problematical because they can produce a number of long-term complications including loss of ability to walk, permanent disability, loss of height and severe back pain(3). Although the precise mechanisms are poorly understood, the hallmark of osteoporosis is a reduction in skeletal mass caused by an imbalance between bone breakdown (resorption) and bone formation. This results in reduced BMD.
However, it’s not just middle-aged and elderly persons who are at direct risk from low BMD/osteoporotic health complications. Research accumulated over the past 20 years or so has demonstrated that low BMD is directly correlated with an increased risk of stress fracture in young athletes(4). This is especially the case in athletes where eating disorders and/or compulsive exercise habits lead to relative energy deficiency in sport (RED-S) (5). For an in-depth discussion of RED-S, the ‘athlete triad’ and the health implications for both male and female athletes, see this article.
Cyclists, swimmers and BMD
Recent evidence shows that cyclists who clock up long hours in the saddle, and swimmers (especially female swimmers) who train long and hard in the pool are likely to have lower levels of BMD than even their sedentary peers, increasing the risk of fracture and also that of osteoporosis in later life(6,7). One potential solution for low-impact athletes such as cyclists and swimmers is to engage in regular impact or weight-bearing activities such as running or weight training. These activities help increase BMD when added to an existing endurance-only program(8). But while this strategy is undoubtedly effective, the downside is time and logistics; adding in extra sessions of another sport or resistance training is not always possible for those with already busy lifestyles. There’s also the issue of ensuring that any additional training complements rather than hinders an existing program.
Shaking things up
In recent years, sports physiologists have looked at alternative methods of increasing BMD – ie other than weight training or high-impact exercise. One option that has come under the spotlight is the use of ‘vibration training’, more accurately known as whole body vibration training (WBVT). WBVT uses high-frequency mechanical stimuli generated by a vibrating platform (for example ‘Power Plate’ – see figure 1) and transmitted through the body. These platforms vary in the type of vibration produced (vertical or side-alternating) and the magnitude of the vibration and frequencies available (although the most common frequencies are in the 30-50Hz range)(9).
Figure 1: Power Plate vibrating platform
The theory is that by standing on the vibrating platform, vibrations can be efficiently transmitted to the large bones in the body. By mimicking bone loading from ground impacts, these vibrations should be able to stimulate bone mass accumulation and improve BMD in those who cannot or do not engage in high-impact exercise. Another claimed benefit is time; due to the large number of vibrations (over 1,800 per minute), WBVT could be a very efficient method of promoting bone health, needing far less time commitment than other modes of exercise. But does this approach stand up to scientific scrutiny?
In one study by South African scientists, researchers looked at the effects of ten weeks of whole body vibration training on the bone density of well-trained road cyclists(10). Fifteen road cyclists were split into two groups:
- Eight cyclists undertook 15 minutes of intermittent whole body vibration at 30Hz, three times per week while continuing with their normal cycling training.
- The remaining seven simply continued with their normal cycling training for the 10-week period without vibration training (the control group).
In addition, the two groups of cyclists were age, body mass and height matched with 15 sedentary subjects for a further comparison. All 30 subjects then underwent regional dual X-ray absorptiometry (DEXA) scans to determine bone mass and BMD levels.
Both the cycling groups had lower pelvic bone mineral density than the sedentary participants with no other differences observed (highlighting the fact that cyclists who just cycle typically have poorer bone density as a result). However, after ten weeks of training, the vibration-trained cyclists showed a significant increase in their hip bone mineral density (a gain of 1.65%) while the control cyclists showed no such gain. Indeed, by the end of the 10-week study period, the control group had a significantly lower spine bone mineral density compared to the start whereas this loss was NOT observed in the vibration-trained group.
Despite the positive results in this study however, other (and more recent) studies have been less clear about the BMD benefits of vibration training. In a 2017 study, researchers investigated the effects of a 6-month period of WBVT on BMD measures in 40 adolescent swimmers(11). As in the cyclist study above, the swimmers were split into two groups, with one adding in 15 minutes of WBVT three times a week. Before and after the six months of training, the BMDs of all the swimmers were measured. The results showed however that adding in WBVT produced no benefits for BMD whatsoever.
The verdict on WBVT and BMD
Given the conflicting results, the obvious question to ask is whether WBVT is a worthwhile BMD-building strategy for athletes seeking optimum bone health? When it comes specifically to athletes, there’s unfortunately a paucity of research findings in the literature. However, a comprehensive review study published last year makes for informative reading(12). This study summarised the findings from 17 other studies on a range of different populations. It concluded that while WBVT seems to help children and adolescents with compromised bone mass to increase BMD, these improvements are limited in postmenopausal women, and there is no evidence of a benefit for healthy young adults. These findings are in line with another (earlier) review study, which found WBVT produced significant but small improvements in BMD in postmenopausal women and children and adolescents, but not in young adults(13).
Vibration vs. resistance training
The evidence to date is that WBVT is far from a universal panacea for bone health in athletes whose sports are low-impact in nature. While the study on cyclists produced encouraging results, the sample size was quite small (making it difficult to draw firm conclusions) and the results were not replicated in the swimmers. One explanation is that while WBVT provides some benefits when BMD is already compromised, the stimulus it generates is not large enough to produce significant gains in people whose BMDs are in the more normal range.
By contrast however, evidence for the efficacy of resistance training as an effective method of building or maintain BMD is far more robust. For example, a large review study conducted by British researchers at the University of Birmingham examined the effect of a resistance training program on musculoskeletal health in 792 older adults across seven separate studies(14). It found that resistance training produced a significant gain in femoral neck BMD – an effect that was further enhanced when the subjects were also supplemented with vitamin D3.
Another review study looked at the effects of different types of exercise programs longer than 24 weeks in women aged 35 to 70 years(15). It found that positive significant changes in lumbar and femoral neck BMD were produced mainly with high-impact exercise/high loading exercise. Interestingly, it also concluded that whole body vibration interventions were also likely to produce a positive effect – possibly to be expected given that many of these sedentary older female subjects already had sub-optimum levels of BMD. These finds fit with those from earlier studies, which have found resistance training alone, or in combination with impact-loading activities, are most osteogenic – in contrast with steady-state, low-impact aerobic type exercise, which has a limited effect on BMD(16-18).
Advice to clinicians
In terms of maximizing bone health in low-impact athletes such as cyclists and swimmers, incorporating some resistance training or high-impact activity into a weekly training program is still recommended. While the addition of WBVT might be beneficial for athletes with clinically proven low BMD levels, this form of training should be considered as an adjunct to resistance/high-impact activities– not as a first resort.
As the clinician or trainer, it is important to prescribe these activities in a progressive fashion, tailored to the individual athlete, with the emphasis on a gradual progression. It’s also important to ensure that the total weekly training load is not increased excessively; this might entail modifying/reducing the existing training load. Needless to say, day-to-day dietary habits are also extremely important for building and maintaining BMD, with a particular emphasis on sufficient calorie intake and calcium/vitamin D rich foods. Where necessary, clinicians should not hesitate to refer athletes onto a dietician or other nutritionally qualified professional.
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