Impact of Loading and Rest Intervals on Muscle Inflammation

Abstract

The efficacy of many existing musculoskeletal disorders (MSDs) treatment and preventive approaches remains unclear in current literature. Instead of applying additional measures that generate additional costs, redesigning the job in a MSD preventive way in the first place could be a cost effective and health promoting alternative. Manipulating rest intervals and load-repetition combinations within the work time and workload capacity constraints could qualify one of the beneficial alternatives. The purpose of this study is to determine whether different load-repetition combinations and rest intervals with different frequencies and durations would have an impact on the inflammatory response of the muscle and the development of MSDs within certain constraints – predetermined total work time, total rest time and total work volume.

In this study, a total of 24 healthy college men with homogenous anthropometry measures will be randomly assigned to a 19-minute bicep eccentric exercise task including a total of 4-minute rest time. The total workload for all eccentric exercise treatment combinations is 27 times the maximum voluntary isometric contraction (MIVC). Within the shift, the subjects will be randomly assigned to 90% MIVC or 30% MIVC workloads; each subject will also be assigned with 2 minutes or 0.5 minute rest intervals. This pilot study uses the recoverable short-term delayed onset muscle soreness (DOMS) analogous to the long-term MSDs to imitate muscle inflammation and healing processes in MSD cases. Three physical responses: serum CK level (a quantitative marker for skeletal muscle microtrauma), MIVC (a good measure of the degree of muscle recovery), and muscle soreness are measured before exercise and at days 1, 2, 4, 8 post-exercise of the human elbow flexor muscles. A two-factor (loading and rest interval) factorial regression model will be established for muscle inflammatory response.

The findings of the study would assist in understanding the effect of loading and rest on muscle inflammatory response and healing process as well as designing jobs with suitable rest intervals and load-repetition balance to prevent MSDs at manufacturing settings. The statistical regression model could provide guidance to implement ergonomic assessment tools.