Gender-Specific Effects of 8-Week Multi-Modal Strength and Flexibility Training on Hamstring Flexibility and Strength

The purpose of this study was to investigate the effects of multi-modal strength training or flexibility training on hamstring flexibility and strength in young males and females. A total of 20 male and 20 female college students (aged 18-24 years) participated in this study and were randomly assigned to either a multi-modal flexibility intervention group or strength intervention group. Passive straight leg raise and isokinetic strength test were performed before and after the intervention to determine flexibility and strength of the participants. Multivariate repeated-measure ANOVA was used to determine the effect of training group and gender on hamstring strength and flexibility. Both male and female participants in the strength intervention group significantly increased peak torque, relative peak torque, and flexibility (all p <= 0.029). Both male and female participants in the flexibility intervention group significantly increased flexibility (both p <= 0.001). Female participants in the flexibility intervention group significantly increased peak torque and relative peak torque (both p <= 0.023). However, no change was seen in peak torque and relative peak torque of male participants in the flexibility intervention group (p >= 0.676). An 8-week strength training program involving various training components can increase flexibility in both males and females, although the flexibility of male participants only increased slightly. While hamstring flexibility training protocol consisted of different types of stretching improved both flexibility and strength in female participants, male participants increased only flexibility but not strength, indicating such effects were gender-specific. For subjects with relatively low strength (e.g., older adults, sedentary women, postoperative rehabilitation population, etc.), strength training alone or flexibility training alone may increase both strength and flexibility.