The purpose of this study was to evaluate age and gender effects on lower limb biomechanics while running. Despite the growing popularity of distance running among middle-aged and older adults, there has been little research studying biomechanical running differences between men and women as they age. The authors hypothesized that regardless of age, women would generate less force with their ankles and quads, but more force with their hips compared to men while running. Based on prior research, the authors also expected less output from the ankle plantarflexors as the runners aged. A total of 47 runners participated in the study, and runners between the ages of 18 and 30 years of age were classified as young, while runners between the ages of 50 and 70 years of age were classified as middle-aged. Regardless of their age group, all runners ran approximately 25 miles per week.

Contrary to their hypothesis, young and middle-aged female runners relied more heavily on their ankle plantarflexors and less so on their hips to generate force. Because they generated a larger percentage of force with their gastrocnemius and soleus muscles, women had higher peak ground reactive forces during their propulsive phase and spent less time on the ground during contact (shorter stance times). As expected, consistent with prior research, male and female athletes generated less force with their ankles as they got older, forcing them to become more reliant on their hip and knee musculature to remain efficient.

 The main finding of this paper was that women plantarflex their ankles during propulsion at a greater speed, which allows them to generate more propulsive ground reactive forces than men while running at the same speed. Because males and females have reduced force output in their calves as they age, the clinical implication of this research is that young males and all middle-aged runners should focus on improving force output in their calves in order to maintain running efficiency, and potentially avoid injuries. The authors also make the interesting observation that because aging reduces gastrocnemius and soleus strength and increases Achilles tendon stiffness, older athletes should be cautious about incorporating midfoot or forefoot strike patterns, as the more forward contact points could result in calf and/or Achilles tendon injuries.