Affiliations: University of Nebraska-Lincoln, Lincoln, NE, USA
Correspondence:
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Corresponding author: Cory M. Smith, Department of Nutrition and Health Sciences, 110 Ruth Leverton Hall, University of Nebraska-Lincoln, Lincoln, NE 68583-0806, USA. Tel.: +1 402 472 2690; E-mail: CSmith@unl.edu.
Abstract: BACKGROUND:Little is known regarding the influence of force application during fatigue when the total amount of work is equal. That is, do changes in force applications result in different fatigue mechanisms despite the overall work being the same. OBJECTIVE:The aim of the current study was to examine the effects of alternating forces versus repeated constant force muscle actions on the time course of changes in neuromuscular responses. METHODS:Sixteen adults performed 50-intermittent isometric leg extensions at alternating 40 then 80% maximal voluntary isometric contraction (40/80% MVIC) or repeated constant forces at 60% MVIC. Each protocol resulted in equal, averaged force across all 50 repetitions. Electromyographic amplitude (EMG RMS), mechanomyographic (MMG) RMS, EMG mean power frequency (MPF), and MMG MPF were recorded from the vastus lateralis. RESULTS:Alternating force protocol resulted in less fatigue-induced changes in neuromuscular responses compared to repeated constant force protocol. The repeated constant force protocol resulted in earlier increases in EMG RMS and MMG RMS as well as earlier decreases in EMG MPF and MMG MPF compared to the alternating force protocol. CONCLUSIONS:Fatigue in occupational, sporting activities, or various fatiguing tasks may be dependent on the order that force is applied.
Keywords: Physical work, loading, work measurement, work physiology, musculoskeletal system
