Abstract
PurposeMountain trekking involves level, uphill, and downhill walking (DW). Prolonged DW induces damage to leg muscles, reducing force generating ability and muscle coordination. These increase risks for more serious injuries and accidents in mountain trekking, thus a strategy to minimize muscle damage is warranted. It has been shown that low-intensity eccentric contractions confer protective effect on muscle damage induced by high-intensity eccentric contractions. This study tested the hypothesis that 5-min non-damaging DW would attenuate muscle damage induced by 40-min DW, but 5-min level walking (LW) would not.MethodsUntrained young men were allocated (n = 12/group) to either a control or one of the two preconditioning groups (PRE-DW or PRE-LW). The PRE-DW and PRE-LW groups performed 5-min DW (-28%) and 5-min LW, respectively, at 5 km/h with a load of 10% body mass, 1 week before 40-min DW (-28%, 5 km/h, 10% load). The control group performed 40-min DW only. Maximal knee extension strength, plasma creatine kinase (CK) activity, and muscle soreness (0–100 mm visual analogue scale) were measured before and 24 h after 5-min DW and 5-min LW, and before and 24, 48, and 72 h after 40-min DW.ResultsNo significant changes in any variables were evident after 5-min DW and 5-min LW. After 40-min DW, the control and PRE-LW groups showed significant (P<0.05) changes in the variables without significant differences between groups (control vs. PRE-LW; peak strength reduction: -19.2 ± 6.9% vs. -18.7 ± 11.0%, peak CK: 635.5 ± 306.0 vs. 639.6 ± 405.4 U/L, peak soreness: 81.4 ± 14.8 vs. 72.0 ± 29.2 mm). These changes were significantly (P<0.05) attenuated (47–64%) for the PRE-DW group (-9.9 ± 9.6%, 339.3 ± 148.4 U/L, 27.8 ± 16.8 mm).ConclusionsThe results supported the hypothesis and suggest that performing small volume of downhill walking is crucial in preparation for trekking.
Highlights
Walking in mountain areas such as trekking is a popular physical activity among many people including seniors around the world [1, 2]
No significant changes in any variables were evident after 5-min downhill walking (DW) and 5-min level walking (LW)
Muscle damage is typically represented by decreased muscle function, delayed onset muscle soreness (DOMS), and increased plasma creatine kinase (CK) activity lasting for several days after exercise, when they are performed for the first time or with a long interval from a previous bout [7]
Summary
Walking in mountain areas such as trekking is a popular physical activity among many people including seniors around the world [1, 2]. Exercises mainly consisting of eccentric contractions induce muscle damage, presumably due to a high strain on weak sarcomeres and/or extra cellular matrix surrounding muscle fibers [5], resulting in micro injuries to contractile proteins such as Z-line and A-band [6]. Falling-related accidents and fatalities during mountain trekking are at least in part attributable to DW-induced muscle damage, in combination with accumulating fatigue from uphill and level walking [1, 2]. Even if accidents are avoided during mountain trekking, muscle damage could affect daily activities for several days, and could increase the risk of injuries [9]. It is of importance to develop an intervention that minimizes DW-induced muscle damage, especially for beginners
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