Knee injury risk - If you're a footballer, your knees are most at risk towards the end of a match

In a new study, in order to investigate whether endurance activities, such as a football match, can increase injury risks in the short term, eight recreational soccer players performed three different endurance runs of 9600 metres - (1) a variable-paced run, mimicking the patterns of soccer play, (2) a shuttle run and (3) a treadmill run. Knee extensor and flexor strength, knee joint laxity and the electromechanical delay (EMD) of the hamstrings were measured before and after each endurance run.

The researchers found that leg strength decreased after all the runs, but more after the shuttle and variable-paced runs. EMD increased after all three runs as did joint laxity, but, again, joint laxity increased more after the variable-paced and shuttle runs.

These results suggest that endurance activities and, in particular, a football match where changes of pace and direction tax the neuromuscular system more, will reduce knee strength and increase knee-injury risks as joint laxity and EMD of the hamstrings increases. Greater joint laxity means that the tibia (shin bone) can be displaced further forward which may strain the anterior cruciate ligament (or ACL, the strap of connective tissue that stabilizes the knee joint), and greater EMD means the hamstrings cannot be recruited as quickly and so will be less effective in controlling ACL strain. This underlines the importance of strength and neuromuscular coordination of the knee joint for soccer players (issue 104 of Peak Performance provides exercises for protecting the ACL).

(Gleeson et al (1998). 'Influence of acute endurance activity on leg neuromuscular and musculoskeletal performance.' Medicine & Science in Sport & Exercise, 30 (4), 596-608)