Prevention of downhill walking-induced muscle damage by non-damaging downhill walking

Purpose: Mountain 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. Methods: Untrained 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. Results: No significant changes in any variables were evident after 5-min DWand 5-min LW. After 40- min DW, the control and PRE-LW groups showed significant (PP Conclusions: The results supported the hypothesis and suggest that performing small volume of downhill walking is crucial in preparation for trekking

Trainability of muscular activity level during maximal voluntary co-contraction: comparison between bodybuilders and nonathletes.

Antagonistic muscle pairs cannot be fully activated simultaneously, even with maximal effort, under conditions of voluntary co-contraction, and their muscular activity levels are always below those during agonist contraction with maximal voluntary effort (MVE). Whether the muscular activity level during the task has trainability remains unclear. The present study examined this issue by comparing the muscular activity level during maximal voluntary co-contraction for highly experienced bodybuilders, who frequently perform voluntary co-contraction in their training programs, with that for untrained individuals (nonathletes). The electromyograms (EMGs) of biceps brachii and triceps brachii muscles during maximal voluntary co-contraction of elbow flexors and extensors were recorded in 11 male bodybuilders and 10 nonathletes, and normalized to the values obtained during the MVE of agonist contraction for each of the corresponding muscles (% EMGMVE). The involuntary coactivation level in antagonist muscle during the MVE of agonist contraction was also calculated. In both muscles, % EMGMVE values during the co-contraction task for bodybuilders were significantly higher (P<0.01) than those for nonathletes (biceps brachii: 66±14% in bodybuilders vs. 46±13% in nonathletes, triceps brachii: 74±16% vs. 57±9%). There was a significant positive correlation between a length of bodybuilding experience and muscular activity level during the co-contraction task (r = 0.653, P = 0.03). Involuntary antagonist coactivation level during MVE of agonist contraction was not different between the two groups. The current result indicates that long-term participation in voluntary co-contraction training progressively enhances muscular activity during maximal voluntary co-contraction

TRUNK MUSCLE ACTIVITIES DURING ABDOMINAL BRACING: COMPARISON AMONG MUSCLES AND EXERCISES

Abdominal bracing is often adopted in fitness and sports conditioning programs. However, there is little information on how muscular activities during the task differ among the muscle groups located in the trunk and from those during other trunk exercises. The present study aimed to quantify muscular activity levels during abdominal bracing with respect to muscle- and exercise-related differences. Ten healthy young adult men performed five static (abdominal bracing, abdominal hollowing, prone, side, and supine plank) and five dynamic (V- sits, curl-ups, sit-ups, and back extensions on the floor and on a bench) exercises. Surface electromyogram (EMG) activities of the rectus abdominis (RA), external oblique (EO), internal oblique (IO), and erector spinae (ES) muscles were recorded in each of the exercises. The EMG data were normalized to those obtained during maximal voluntary contraction of each muscle (% EMGmax). The % EMGmax value during abdominal bracing was significantly higher in IO (60%) than in the other muscles (RA: 18%, EO: 27%, ES: 19%). The % EMGmax values for RA, EO, and ES were significantly lower in the abdominal bracing than in some of the other exercises such as V-sits and sit-ups for RA and EO and back extensions for ES muscle. However, the % EMGmax value for IO during the abdominal bracing was significantly higher than those in most of the other exercises including dynamic ones such as curl-ups and sit-ups. These results suggest that abdominal bracing is one of the most effective techniques for inducing a higher activation in deep abdominal muscles, such as IO muscle, even compared to dynamic exercises involving trunk flexion/extension movement

Changes in muscle soreness following 40-min downhill walking.

<p>Changes in muscle soreness of the anterior thigh assessed by a visual analog scale (VAS) before (pre), and 24, 48, and 72 hours after 40-min downhill walking for the preconditioning downhill walking (PRE-DW, closed triangle), preconditioning level walking (PRE-LW, closed circle), and control (open circle) groups. Values are means ± SDs. A cross mark (†) indicates a significant (<i>P</i> < 0.05) difference between groups based on a one-way ANOVA.</p

Efficacy of downhill running training for improving muscular and aerobic performances

This study investigated effects of downhill (DR) versus level (LR) running training on various muscular and aerobic performances. Eighteen healthy young males conducted either DR (DR group [DRG], n = 10: -10% slope) or LR (LR group [LRG], n = 8) training at a target heart rate (HR) associated with lactate threshold (LT) for 20 min·sessionThe accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Changes in plasma creatine kinase activity following 40-min downhill walking.

<p>Changes in plasma creatine kinase (CK) activity before (pre), and 24, 48, and 72 hours after 40-min downhill walking for the preconditioning downhill walking (PRE-DW, closed triangle), preconditioning level walking (PRE-LW, closed circle), and control (open circle) groups. Values are means ± SDs. An asterisk (*) indicates a significant (<i>P</i> < 0.05) difference from the pre-value (baseline). A cross mark (†) indicates a significant (<i>P</i> < 0.05) difference between groups based on a two-way and subsequent one-way ANOVA.</p

Changes in maximal strength following 40-min downhill walking.

<p>Changes in maximal voluntary isometric contraction (MVC) torque of the knee extensors before (pre), and 24, 48, and 72 hours after 40-min downhill walking for the preconditioning downhill walking (PRE-DW, closed triangle), preconditioning level walking (PRE-LW, closed circle), and control (open circle) groups. Values are means ± SDs. An asterisk (*) indicates a significant (<i>P</i> < 0.05) difference from the pre-value (baseline). A cross mark (†) indicates a significant (<i>P</i> < 0.05) difference between groups based on a two-way and subsequent one-way ANOVA.</p

Schematic diagram of the experimental design.

<p>The measurements were taken before and 24 h after 5-min DW and 5-min LW, and before and 24, 48, and 72 h after 40-min DW.</p

Involuntary antagonist coactivation level during MVE of agonist contraction.

<p>Involuntary antagonist coactivation level (% EMG_MVE) during MVE tasks in bodybuilders (circle) and nonathletes (square). The % EMG_MVE values for both biceps brachii (during elbow extension MVE: 9±4% vs. 9±6%) and triceps brachii muscles (during elbow flexion MVE: 9±6% vs. 12±6%) were not different between groups. Open and closed symbols indicate individual and mean values, respectively.</p