Posted: November 5, 2004

Science of Sport: A 10-K "Shadow" On Your Legs

Completing a 10-K race can knock the stuffing out of your leg muscles. If you don't believe that, try running as fast as possible in a 10-K competition the day after your next regular 10K. Generally, you will find that your performance will be sub-par and that your legs will feel "heavy" during the second race. What causes this decline in performance after an intense 10-K exertion, and how long does the decrement in exercise capacity last? In addition, when will your leg muscles have recovered enough (following a 10-K ramble) to carry out high-quality training once again?

To find out the answers to these questions, researchers at the University of Connecticut, Pennsylvania State University, Ball State University in Indiana, and the University of Jyvaskyla in Finland recently studied 10 healthy, fit men who were experienced distance runners. The 10 subjects were recruited from local track clubs and were training for 10-K racing; many were former collegiate endurance runners. Average age was 22, mean percent body fat settled at a lean 9%, and VO2max averaged a somewhat lofty 64 ml/kg-min.

For all of the athletes, maximal muscular strength and power during knee flexion and extension were measured at various speeds using a System II Biodex isokinetic dynamometer two days before a 10K, 15 minutes after the 10-K race, and two days post-race. On the same dates, muscular endurance was assessed during 50 repetitions of voluntary maximal isokinetic knee extensions and flexions at a speed of 180 degrees per second. Jumping ability was gauged utilizing a standing counter-movement vertical jump test. The race itself was held on a standard, all-weather, 400-meter competitive outdoor track, and the goal of each subject was to set a personal record.

The actual 10-K race times ranged from 32:22 to 37:09, with a mean of 35:12. This represented a "98-% effort" for the group of 10 runners, based on their pre-established personal records. Interestingly enough, average heart rate at the end of the race reached 98% of max, too. Immediately after the race, there was a significant decrease in peak torque produced by the hamstrings during knee flexion at a speed of 30 degrees per second. This loss was restored after 48 hours, however. During the 50-repetition test, the hamstrings exhibited losses in total exercise capacity and average power immediately after the race, but these values also returned to normal 48 hours post-race. However, total work performed by the hamstrings over the last 17 reps of the 50-repetition test was significantly reduced right after the race - and also after 48 hours, indicating that the hams had not completely restored their ability to perform work of an endurance nature. In addition, significant reductions in peak vertical jump force remained reduced 48 hours after the 10-K effort.

These results indicate that the hamstrings are damaged enough from a 10-K race so that recovery of normal function is not complete within a 48-hour, post-competition period. It is not particularly surprising that the hamstrings are affected so strongly by 10-K running. The key role played by the hams during endurance running is to control forward acceleration of the leg during the "swing" phase of the gait cycle. This, of course, is an eccentric action by the hamstrings (in which they are producing force while being stretched), and eccentric muscular activities are noted for their tendency to induce injury and to reduce muscle function. A 10-K race is very likely to produce significant small-scale hamstring trauma, since the competition is generally sustained for over 30 minutes and the speeds attained are quite high (and thus the accelerating forces acting on the hamstrings are quite lofty). With a standard stepping rate of 180 steps per minute, a 10-K runner exerting close-to-maximal effort for 35 minutes would put each set of hamstrings under intense eccentric strain a total of 3,150 times.

Of course, there are practical applications associated with these findings. If you have scheduled a 10-K race for yourself, it probably makes sense to wait at least 72 hours post-race before conducting a highly strenuous running workout. It is hoped that the extra 24 hours (above and beyond 48 hours, which were not enough for hamstring recovery in the research) would permit more-complete functional restoration of the hammies. This should minimize further damage to the hams which might accrue during the workout, and it should permit the workout itself to be higher in quality, too (compared to one conducted 48 hours after the race).

An application which is usually forgotten when studies such as these are published is that athletes should do things in training which minimize the kind of hamstring trauma experienced by the 10-K runners in this study. In particular, athletes who engage in sustained, hard running should develop a close-to-religious devotion to training exercises and drills which fortify the hamstrings during eccentric activity, including high-bench step-ups and bicycle leg swings (with and without resistance). Adherence to these exercises during training should strengthen the hams enough so that damage during intense efforts like a 10-K race is reduced. Thus, recovery will be quicker, and the chances of developing a significant hamstring problem will be diminished.

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Reference:

(1) "The Effects of a 10-Kilometer Run on Muscle Strength and Power," Journal of Strength and Conditioning Research, Vol. 16(2), pp. 184-191, 2002

By Owen Anderson, Ph. D.

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