Repeated bout effect conferred by downhill backward walking

Abstract or Summary

Downhill backward walking has been shown to induce muscle damage to the triceps surae muscles, however it is not known how the muscles respond to a repeated bout of the same exercise. This study compared the changes in indirect markers of muscle damage following an initial and secondary bout of downhill backward walking. Seventeen subjects completed two 60 min bouts of downhill (-15%) backward walking (30 – 35 strides/min) separated by two weeks. A two-way repeated measures ANOVA demonstrated significant (p<0.05) increases in soreness (bout 1: 6.2 ± 2.5; bout 2: 3.1 ± 2.1) and tenderness (bout 1: 48.0 ± 28.9 kPa; bout 2 – 57.6 ± 30.5 kPa) following both exercise bouts, however, the severity was significantly (p<0.0083) lower after bout two. Plasma creatine kinase activity increased significantly (p<0.05) following bout one only (peak: 497.6 ± 401.2 IU/L). Significant decreases (p<0.05) in isometric strength occurred after both bouts (bout 1: ~20%; bout 2: ~18%), but the recovery was significantly (p<0.0083) faster after the second bout. Significant decreases (p<0.05) in isokinetic strength (~17%) were evident following the initial exercise bout only. The attenuated responses following the second bout indicate that the initial downhill backward walking bout conferred the repeated bout effect. It appears that eccentric loading to the muscles during downhill backward walking exceeded that of daily activity in volume and strain, and this generated the effect.