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THE EFFECT OF LOCOMOTOR-RESPIRATORY COUPLING ON HANDGRIP MUSCLE STRENGTH AND ENDURANCE

Abstract

Locomotor-Respiratory Coupling (LRC) is the synchronization of rhythmic locomotion and breathing. Although the phenomenon has been historically associated with activities such as running, it is unclear if LRC plays a role in other types of repetitive muscular contractions. PURPOSE: Determine effects of LRC on handgrip muscle strength and endurance. METHODS: Using randomized and repeated measures design, participants (n = 25; 14 male, 11 female; 23 ± 3 yrs age) completed multiple trials of handgrip strength and endurance testing on two days (counterbalancing left and right handgrip trials). Instrumentation included digital handgrip dynamometer and chest-mounted pressure transducer (to verify breathing cadence) interfaced with data acquisition system (sampling 1000 Hz). To assess the effect of LRC on maximal force production, each testing day included multiple 30 s trials of repetitive maximum handgrip (frequency = 30 bpm) utilizing a LRC strategy of either two squeezes to one breath ratio (2:1) or three squeezes to one breath ratio (3:1). Trials were completed with each hand and rest periods were incorporated to minimize fatigue. To assess effect of LRC on muscular endurance, participants completed 120 s trials of maximal repetitive squeezes (57 bpm) for each hand, either inspiring during each contraction (Inspiration-Motor Coupling, IMC) or expiring during contraction (Expiration-Motor Coupling, EMC). To quantify level of resultant fatigue (i.e. muscular endurance), % change of peak force from initial to final represented degradation of handgrip muscle force over time. RESULTS: Paired t-tests revealed 2:1 breathing ratio increased maximal handgrip force as compared to 3:1 breathing ratio (158 ± 63 N, 146 ± 55 N, respectively; p < 0.01). Although the endurance protocol was deemed valid, as shown by decrement of peak force from initial to ending point in both breathing conditions (IMC = 35 ± 12 % decline, p < 0.01; EMC = 37 ± 12 % decline, p < 0.01), there was no difference in level of fatigue between IMC and EMC. CONCLUSION: Although our study showed no effect of LRC on muscular endurance, our findings did indicate a 2:1 breathing ratio is more effective than 3:1 for enhancing muscle strength during short duration, repetitive activities. Future research should investigate the efficacy of additional LRC breathing ratios.

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