Impact of loading and work rest intervals on muscle micro-trauma

Abstract

PurposeTo examine whether rest intervals of different durations (“High Rest, Low Frequency” v. “Low Rest, High Frequency”), and load at different force exertion levels with different repetition frequencies (“High Load, Low Repetition” v. “Low Load, High Repetition”) have an impact on muscle micro-trauma, as such micro-trauma over repetitive loading and long-term muscle overuse can lead to musculoskeletal disorders (MSDs). MethodTwenty-four adult males (mean age: 24.1 years; 3.6 SD) were randomly assigned to one of 4 bicep muscle eccentric exercise treatment groups (n = 6; “High Load, Low Repetition; High Rest, Low Frequency”, “High Load, Low Repetition; Low Rest, High Frequency”, “Low Load, High Repetition; High Rest, Low Frequency”, or “Low Load, High Repetition; Low Rest, High Frequency”) with non-dominant arm to induce muscle micro-trauma reactions in serum. Subjects in all treatment groups had equivalent total work volume, total rest duration and total work duration for comparison of muscle micro-trauma between and within the treatment groups. Muscle micro-trauma biomarker serum Creatine Kinase (CK) level was measured pre-exercise (Day 0) and post-exercise on Days 1, 2, 4, and 8. ANOVA with repeated measures was used to examine significance of rest and load-repetition combination over pre and post experiment days, as well as possible interactions. ResultCK levels fluctuated significantly across different “Day” (P = 0.0115). Interaction was disordinal and significant between “Day” and “Rest” (P = 0.0000), and “Load” and “Rest” (P = 0.0322). Under “High Load, Low Repetition” condition, CK levels on Day 4 were significantly higher than on Days 0 and 2; CK levels on Day 8 were significantly higher than Day 0. CK level peaked on Day 4. Under “Low Rest” Condition, CK level on Days 4 and 8 are significantly higher than Day 0. ConclusionShorter but more frequent rest intervals led to more extreme muscle micro-traumatic responses than the longer but less frequent ones, especially under “High Load, Low Repetition” condition when non-dominant bicep brachii was subscribed with eccentric exercise regimen. Relevance to industryThe exploration of how rest scheduling affects progression of microtrauma from a biomechanical and molecular level in this study furthers current understanding of the early stage development of WMSDs. With future studies’ further research and confirmation, the findings of this study may be able to serve as a first attempt to guide shift scheduling and job design at manufacturing facilities.