Muscle work discrepancy during incline and decline running at three speeds

Introduction. Previous research has explored muscle function during gait and this work has shown that more positive mechanical muscle work is produced in gait tasks that primarily raise the center of mass (incline gait tasks) compared to the amount of negative mechanical muscle work dissipated in gait tasks that primarily lower the center of mass (decline gait tasks). This has led to the hypothesis that skeletal muscles generate more mechanical energy in gait tasks that raise the center of mass compared to mechanical energy dissipated by muscles in gait tasks that lower the center of mass. The purpose of this study was to compare the positive and negative muscle work produced during incline and decline running at three speeds in healthy young adults.;Methods. Three-dimensional gait analysis was performed to compare the kinetic and energetic differences between incline and decline running on 20 healthy runners (mean age 20.5 years) at speeds of 2.68 m/s, 3.35 m/s, and 4.47 m/s. Positive and negative muscle work in all three planes during the stance phase were derived from the power curves and compared across speeds. Muscle work from both the incline and decline running conditions were analyzed using a two-factor analysis of variance (ANOVA). Mean differences with alpha levels below 0.05 were considered significant.;Results. Incline running had 36% more net muscle work compared to decline running (p<0.001). A significant interaction effect between gait direction and running speed was found such that the difference between positive and negative work increased with running speed (p<0.001).;Discussion. The results of this work show that muscles produce and dissipate work differently during incline and decline running. Several reasons for the difference in muscle work have been identified which include: increased vibrational motion of soft tissues, poorer mechanical advantage in incline compared to decline running, and longer stride lengths in decline vs. incline running. The data of the present study support the hypothesis that skeletal muscles generate more mechanical energy in gait tasks that raise the center of mass compared to mechanical energy dissipated by muscles in gait tasks that lower the center of mass.