Objective: In recent years, it has been focused much attention on gait analysis. Factors such as speed, age and gender affect gait parameters. The purpose of the present study was to compare the electromyographic activity pattern of knee two-joint muscles between younger and older subjects in different gait speeds.

Matterials & Methods: The method of current study was analytical cross-sectional method in which 15 healthy young men and 15 old men, were selected conveniently. Electromyographic activity of rectus femoris, biceps femoris, semitendinus and gastrocenemius were recorded during walking with preferred (100%), slow (80%) and fast (120%) speeds in a 10 meter walkway. Normalized RMSs of muscles were compared using RM-ANOVA and Tokey’s tests by SPSS 18 software.

Results: According to results, RMSs of rectus femoris in midstance (P<0.01) and gastrocenemius in loading response (P=0.02) phases in all walking speeds were higher in older subjects than in younger ones, and it increased with speed in both age groups (P<0.01). Biceps femoris RMS in terminal stance at 80% speed, was lower in older subjects than in younger ones (P=0.01) and it increased with walking speed (P=0.01). Semitendinus activity in loading and midstance phases at 120% speed was higher in older subjects than in younger ones (P<0.01), and it increased with speed in both age groups in swing phase (P<0.05).

Conclusion: According to the results, older subjects have more muscle co-contraction around knee at high speed in midstance phase than younger subjects. These age-related changes in muscle activity, leads to increase in joint stiffness and stability during single support, and probably play a role in reducing push off power at faster speeds.