The Science of Muscle Strengthening


by Dr. Reed Ferber, Ph.D. CAT(C)

Dating back to 2005, research from our laboratory and others from around the world has focused on how improving muscle strength can help runners. For example, we published a study on runners with patellofemoral pain (PFP), often called “runner’s knee” and identified by pain under the kneecap. The runners in the study performed two simple hip-muscle strengthening exercises every day for three weeks.

At the end of the three-week program, runners had a 43% reduction in pain and a 30% increase in muscle strength. In such a short period of time, improvements in strength are largely attributable to changes in neuromuscular activation of muscles and not to changes in muscle fibre composition. In other words, the nervous system was better activated and caused more muscle fibres to contract, but there were no changes to the muscle composition itself. Changes in muscle composition (also called hypertrophy) relate to the enlargement of muscle fibres. This means if the runner experiences a decrease in pain and ceases to do the exercises after two or three weeks, any strength that was gained will be quickly lost. It takes approximately five to six weeks for the composition of the muscle to actually change, hypertrophy to begin, and long-lasting effects to take place. In fact, we published a more recent study in which runners with PFP underwent a six-week muscle strengthening program and then stopped performing the exercises altogether. Six months later, they only had a 6 to 10% decrease in muscle strength and only 5% of them had a reoccurrence in knee pain.

How can strength training improve my running?
Unfortunately, no studies have been conducted on long-distance (recreational or competitive) runners to understand the effects of muscle strengthening on overall performance. As such, I cannot speak to how these types of exercises will help you reach a personal best time. However, our research was one of the first to show that muscle strengthening results in a reduction in stride-to-stride variability; in other words, a more consistent running gait pattern on a step-by-step basis. From a clinical perspective, it is reasonable to assume that restoration of a more consistent and predictable movement pattern would occur alongside increases in muscle strength and reductions in pain. If your key stabilizing muscles are weak, there is a lot of muscle compensation—other muscles doing the work of your stabilizing muscles—which results in a less consistent, more variable gait pattern. However, increases in muscle strength results in less compensation and a more consistent gait pattern. If you’re not injured, the improved muscle strength will be injury protective since any minor compensations, due to even small amounts of muscle weakness, can be reversed and your body knows what to expect on each step.

How many sets and reps should I perform?
Funny thing… one day back in the 1930s, someone simply thought that 3 sets of 10 repetitions sounded like a good idea. Unfortunately, no studies have been conducted to determine if 4 sets of 17 repetitions, or maybe even 6 sets of 6 repetitions, would be better. Regardless, the practice of 3 sets of 10 reps is most commonly used throughout clinical research. There is also strong evidence that performing strengthening exercises every day, using lighter resistance such as an elastic band, is better than doing strengthening work two or three times a week using heavier weights. So, if you make muscle strengthening part of your daily routine, you’ll begin to feel the benefits in a few weeks.

One important principle to keep in mind, though: always perform muscle strengthening exercises after a run—never immediately before. These are your key stabilizing muscles and if these exercises are done before a run, the risk of injury increases due to fatigue.

Standing Hip Abductor Exercise
Place outside foot in band, with the band passing in front of your standing leg. Move involved leg outward, keeping knee straight. Movement should take 2 seconds to stretch out and 2 seconds to return to start position. Keep control of the motion throughout the exercise. Perform on each leg for an equal number of repetitions.


Dr. Reed Ferber is the director of the Running Injury Clinic, a world leader in running-related research and 3D gait analysis technology. For more information, visit

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