Running is a popular and beneficial form of exercise, but has notoriously high injury rates. Since most running injuries are overuse injuries, it is possible these injury rates could be reduced by adjusting running form to reduce musculoskeletal loading. One modification that has been suggested for reducing injury risk is changing foot strike pattern. The majority of recreational runners land on their heels when running, which is known as rearfoot striking. However, converting to forefoot striking and landing on the ball of the foot rather than the heel may be useful for reducing overuse injuries. Understanding the differences between rearfoot and forefoot striking during running and how these differences affect injury risk is necessary before promoting one foot strike pattern as protective.

I began by identifying the differences in muscle activities of ten major lower limb muscles between habitual rearfoot striking and habitual forefoot striking runners. I compared average muscle activity, normalized to peak activity during walking, during the terminal swing phase and early stance phase of gait. From this analysis, I discovered greater muscle activity in the medial and lateral gastrocnemius, but reduced activity in the tibialis anterior, medial vasti and lateral hamstrings during forefoot striking. Understanding how muscle activities differ between these running patterns can provide insight into how the types of injuries sustained may differ based on foot strike pattern and potentially suggests strengthening the medial and lateral gastrocnemii before converting to forefoot striking.

To improve the understanding of how modifying foot strike pattern may reduce injury risk, I observed the effect of acute gait retraining in habitual rearfoot striking runners on biomechanical parameters associated with tibial stress fractures. I collected data on runners using their habitual rearfoot striking pattern as well as using two types of running pattern modifications that are thought to reduce injury risk:​ converting to forefoot striking and increasing cadence by 10%. After comparing the injury risk parameters between these three different running patterns, I found that rearfoot striking did not demonstrate any benefits over forefoot striking or increasing cadence. Forefoot striking was able to reduce peak and average loading rate. Increasing cadence was able to reduce peak hip adduction angle. From this study, I found that forefoot striking and increasing cadence may be beneficial for decreasing the risk of tibial stress fractures during running, but these modifications likely do so using different mechanisms.

Finally, I analyzed the effect of converting to a forefoot striking pattern on plantar flexor muscle-tendon dynamics. I created simulations, driven by kinematics and electromyography data, of habitual rearfoot striking runners using both foot strike patterns to understand how demands placed on these muscles change with foot strike pattern. With these simulations, I examined how foot strike pattern affected positive and negative work done by the gastrocnemius and soleus muscle fibers, tendons, and muscle-tendon units, and estimated the effect of foot strike on these muscles’ ability to generate active force. I found that although the total energy storage in the Achilles tendon was not different between rearfoot and forefoot striking, forefoot striking placed greater demands on the gastrocnemius and reduced demands on the soleus. Forefoot striking increases activation of the gastrocnemius and takes advantage of the muscle fibers’ greater capacity to generate active force which results in greater forces, eccentric contraction rather than concentric contraction during early stance, and increased negative work done by the fibers. In contrast, forefoot striking decreases the activation of the soleus, causing the soleus fibers to do less positive work. Analyzing these simulations can provide insight into the importance of strengthening the gastrocnemius before converting to forefoot striking.

The findings of this work strengthen the understanding of differences between rearfoot and forefoot striking. Comparing muscle activity differences between habitual rearfoot and habitual forefoot strikers provides insight into how demands placed on the muscles differ between runners adapted to different running styles. By examining the effects of acute gait retraining in habitual rearfoot striking runners, it is possible to gain insight into how injury risk parameters and muscle-tendon dynamics change when first adapting to forefoot striking. Although I cannot claim that forefoot striking is the optimal running pattern for reducing all injuries, converting to forefoot striking may be beneficial for reducing the risk of tibial stress fractures. Furthermore, based on greater demands placed on the gastrocnemius after acute adaptation, I advise runners who are interested in forefoot striking to take precautions when experiencing calf soreness and to consider converting slowly. This work, using both experiments and simulations, has brought us closer to understanding how the differences between rearfoot striking and forefoot striking may affect injury risk and is a first step toward reducing overuse injuries using recommendations of running modifications.