Completing a 10K race can knock the stuffing out of your leg muscles. If you don’t believe it, try running as fast as possible in a 10K 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 10K exertion, and how long does the decrement in exercise capacity last? In addition, when will your leg muscles have recovered enough (following a 10K competition) to carry out high-quality training once again? If you are running 10K heats in national or international competitions, can you expect to be up-to-par again 48 hours after your first 10K, or does it take longer?

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 Effects of a 10-Kilometer Run on Muscle Strength and Power,‘ Journal of Strength and Conditioning Research, Vol. 16(2), pp. 184-191, 2002.) The 10 subjects were recruited from local track clubs and were training for 10K racing; many were former college 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 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 pre-race, 15 minutes after the 10K 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 utilising a standing counter-movement vertical jump test. The race itself was held on a standard, all-weather, 400-metre competitive outdoor track, and the goal of each subject was to set a personal record.

The actual 10K 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. 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 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 10K effort.

Why the hamstrings are affected so strongly

These results indicate that the hamstrings are damaged enough from a 10K race so that recovery of normal function is not complete within 48 hours post-competition. It is not particularly surprising that the hamstrings are affected so strongly by 10K running. The key role played by the hams during endurance effort 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 high). With a standard stepping rate of 180 steps per minute, it is estimated that a 10K 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 10K 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) would permit more-complete functional restoration of the hamstrings.

Naturally, if you find yourself running 10K heats in major competitions which are spaced 48 hours apart, it makes sense to try to qualify in the first heat without running one’s best time. The faster the first-heat effort, the greater will be the strain on the ‘strings.

An application which is usually forgotten when studies such as these are published is that athletes should do things in training which minimise the kind of hamstring trauma experienced by the 10K 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 10K race is reduced. Thus, recovery will be quicker.