Non-invasive assessment of fatigue and recovery of inspiratory rib cage muscles during endurance test in healthy individuals.

INTRODUCTION: Fatigue is defined as loss of capacity to develop muscle force and/or velocity that is reversible at rest. We assessed non-invasively the fatigue and recovery of inspiratory rib cage muscles during two respiratory endurance tests in healthy individuals. METHODS: The sniff nasal inspiratory pressure (SNIP) was assessed before and after two respiratory endurance tests: normocapnic hyperpnea (NH) and inspiratory pressure threshold loading (IPTL). Contractile (maximum rate of pressure development and time to peak pressure) and relaxation parameters (maximum relaxation rate [MRR], time constant of pressure decay [τ], and half relaxation time) obtained from sniff curves and shortening velocity and mechanical power estimated using optoelectronic plethysmography were analyzed during SNIP maneuvers. Respiratory muscle activity (electromyography) and tissue oxygenation (near-infrared spectroscopy-NIRS) were obtained during endurance tests and SNIP maneuvers. Fatigue development of inspiratory rib cage muscles was assessed according to the slope of decay of median frequency. RESULTS: Peak pressure during SNIP decreased after both protocols (p <0.05). MRR, shortening velocity, and mechanical power decreased (p <0.05), whereas τ increased after IPTL (p <0.05). The median frequency of inspiratory rib cage muscles (i.e., sum of sternocleidomastoid, scalene, and parasternal) decreased linearly during IPTL and exponentially during NH, mainly due to the sternocleidomastoid. CONCLUSION: Fatigue development behaved differently between protocols and relaxation properties (MRR and τ), shortening velocity, and mechanical power changed only in the IPTL.

Repetition Failure Occurs Earlier During Low-Load Resistance Exercise With High But Not Low Blood Flow Restriction Pressures: A Systematic Review and Meta-analysis.

ABSTRACT: Cerqueira, MS, Lira, M, Mendonça Barboza, JA, Burr, JF, Wanderley e Lima, TB, Maciel, DG, and De Brito Vieira, WH. Repetition failure occurs earlier during low-load resistance exercise with high but not low blood flow restriction pressures: a systematic review and meta-analysis. J Strength Cond Res XX(X): 000-000, 2021-High-load and low-load resistance training (LL-RT) performed to failure are considered effective for improving muscle mass and strength. Alternatively, LL-RT with blood flow restriction (LL-BFR) may accelerate repetition failure and has been suggested to be more time efficient than LL-RT. This study explores the evidence for the effects of LL-BFR vs. LL-RT on repetition failure. A systematic literature search was conducted in the PubMed, CINAHL, Web of Science, CENTRAL, Scopus, SPORTDiscus, and PEDro databases. Meta-analyses of mean differences and 95% confidence intervals (CIs) were performed using a random-effects model. Subgroup analyses were conducted for both the high and low blood flow restriction pressures. The search identified n = 10 articles that met the inclusion criteria. The meta-analysis comprised a total of 218 healthy subjects. Low-load resistance training with blood flow restriction with high pressures (≥50% arterial occlusion pressure [AOP]) precipitate repetition failure in ∼14.5 fewer repetitions (95% CI -19.53 to -9.38) compared with LL-RT, whereas the use of low pressures (<50% AOP) stimulated repetition failure with ∼1.4 fewer repetitions (95% CI -3.11 to 0.37); however, this difference was not statistically significant. Repetition failure has been demonstrated to be an important normalizing variable when comparing the hypertrophic and strength effects resulting from resistance training and occurs earlier during low-load resistance exercise with high but not low blood flow restriction pressures.