Male and female runners demonstrate different sagittal plane mechanics as a function of static hamstring flexibility

Abstract

Background: Injuries to runners are common. However, there are many potential contributing factors to injury. While lack of flexibility alone is commonly related to injury, there are clear differences in hamstring flexibility between males and females.

Objective: To compare the effect of static hamstring length on sagittal plane mechanics between male and female runners.

Method: Forty subjects (30.0±6.4 years) participated and were placed in one of 4 groups: flexible males (n=10), inflexible males (n=10), flexible females (n=10), and inflexible females (n=10). All subjects were free of injury at the time of data collection. Three-dimensional kinematics and kinetics were collected while subjects ran over ground across 2 force platforms. Sagittal plane joint angles and moments were calculated at the knee and hip and compared with a 2-way (sex X flexibility) ANOVA (α=0.05).

Results: Males exhibited greater peak knee extension moment than females (M=2.80±0.47, F=2.48±0.52 Nm/kg*m, p=0.05) and inflexible runners exhibited greater peak knee extension moment than flexible runners (In=2.83±0.56, Fl=2.44±0.51 Nm/kg*m, p=0.01). For hip flexion at initial contact, a significant interaction existed (p<0.05). Flexible females (36.7±7.4º) exhibited more hip flexion than inflexible females (27.9±4.6º, p<0.01) and flexible males (30.1±9.5º, p<0.05). No differences existed for knee angle at initial contact, peak knee angle, peak hip angle, or peak hip moment.

Conclusion: Hamstring flexibility results in different mechanical profiles in males and females. Flexibility in the hamstrings may result in decreased moments via active or passive tension. These differences may have implications for performance and injury in flexible female runners.

Figure 1.. Measurement of hamstring flexibility. Measurements were taken with a goniometer modified with extended arms. The stationary arm was held vertical and in alignment with the upper leg. This was verified with a bubble level. The movement arm was held in line with the fibula extended through the lateral malleolus. A second examiner provided consistent force measured with a handheld dynamometer while examiner one recorded the final angle.

Figure 2.. Retroreflective marker placement. A total of 39 markers were placed with at least 3 markers per segment were placed on the pelvis, thighs, shanks, and feet for tracking during running. Static markers were placed over the joints in order to establish anthropometrics and segment coordinate systems.

Figure 3.. Sagittal plane hip angle during stance. Note that flexible females demonstrate greater hip flexion at initial contact that does not exhibit the same flexion absorption as the other groups. FF=flexible females; FM=flexible males; IF=inflexible females; IM=inflexible males.