Optimal load for a torque-velocity relationship test during cycling.

PURPOSE: Lower limbs' neuromuscular force capabilities can only be determined during single sprints if the test provides a good fit of the data in the torque-velocity (T-V) and power-velocity (P-V) relationships. This study compared the goodness of fit of single sprints performed against traditional (7.5% of the body mass) vs. optimal load (calculated based on the force production capacity and ergometer specificities), and examined if reducing the load in fatigued state enhances T-V and P-V relationship goodness of fit. METHODS: Thirteen individuals performed sprints before (PRE) and after (POST) a fatiguing task against different loads: (1) TRAD: traditional, (2) OPT: optimal, and (3) LOW-OPT: optimal load reduced according to fatigue levels. RESULTS: At PRE, OPT sprints presented a higher R2 of the T-V relationship (0.92 ± 0.06) and lower time to reach maximal power (Pmax) (48 ± 9%) when compared with TRAD sprints (0.89 ± 0.06 and 66 ± 22%, respectively, p < 0.01). At POST, the range of velocity spectrum was greater in the LOW-OPT (33 ± 4%) vs. TRAD (24 ± 3%) and OPT (26 ± 8%, p < 0.007). Similarly, the time to reach Pmax was lower in the LOW-OPT (46 ± 12%) vs. TRAD (76 ± 24%) and OPT (70 ± 24%, p < 0.006). CONCLUSION: Sprints performed against an OPT load and reducing the OPT load after fatigue improve the fit of data in the T-V and P-V curves. Sprints load assignment should consider force production capacities rather than body mass.

Vascular and oxygenation responses of local ischemia and systemic hypoxia during arm cycling repeated sprints.

OBJECTIVES: The purpose of this study was to investigate the acute vascular and oxygenation responses to repeated sprint exercise during arm cycling with either blood flow restriction (BFR) or systemic hypoxia alone or in combination. DESIGN: The study design was a single-blinded repeated-measures assessment of four conditions with two levels of normobaric hypoxia (400 m and 3800 m) and two levels of BFR (0% and 45% of total occlusion). METHODS: Sixteen active participants (eleven men and five women; mean ± SD; 26.4 ± 4.0 years old; 73.8 ± 9.8 kg; 1.79 ± 0.07 m) completed 5 sessions (1 familiarization, 4 conditions). During each test visit, participants performed a repeated sprint arm cycling test to exhaustion (10 s maximal sprints with 20 s recovery until exhaustion) to measure power output, metabolic equivalents, blood flow, as well as oxygenation (near-infrared spectroscopy) of the biceps brachii muscle tissue. RESULTS: Repeated sprint performance was decreased with both BFR and systemic hypoxia conditions. Greater changes between minimum-maximum of sprints in total hemoglobin concentration (Δ[tHb]) were demonstrated with BFR (400 m, 45% and 3800 m, 45%) than without (400 m, 0% and 3800 m, 0%) (p < 0.001 for both). Additionally, delta tissue saturation index (ΔTSI) decreased more with both BFR conditions than without (p < 0.001 for both). The absolute maximum TSI was progressively reduced with both BFR and systemic hypoxia (p < 0.001). CONCLUSIONS: By combining high-intensity, repeated sprint exercise with BFR and/or systemic hypoxia, there is a robust stimulus detected by increased changes in blood perfusion placed on specific vascular mechanisms, which were more prominent in BFR conditions.

Neuromuscular evaluation of arm-cycling repeated sprints under hypoxia and/or blood flow restriction.

PURPOSE: This study aimed to determine the effects of hypoxia and/or blood flow restriction (BFR) on an arm-cycling repeated sprint ability test (aRSA) and its impact on elbow flexor neuromuscular function. METHODS: Fourteen volunteers performed an aRSA (10 s sprint/20 s recovery) to exhaustion in four randomized conditions: normoxia (NOR), normoxia plus BFR (NBFR), hypoxia (FiO2 = 0.13, HYP) and hypoxia plus BFR (HBFR). Maximal voluntary contraction (MVC), resting twitch force (Db10), and electromyographic responses from the elbow flexors [biceps brachii (BB)] to electrical and transcranial magnetic stimulation were obtained to assess neuromuscular function. Main effects of hypoxia, BFR, and interaction were analyzed on delta values from pre- to post-exercise. RESULTS: BFR and hypoxia decreased the number of sprints during aRSA with no significant cumulative effect (NOR 16 ± 8; NBFR 12 ± 4; HYP 10 ± 3 and HBFR 8 ± 3; P < 0.01). MVC decrease from pre- to post-exercise was comparable whatever the condition. M-wave amplitude (- 9.4 ± 1.9% vs. + 0.8 ± 2.0%, P < 0.01) and Db10 force (- 41.8 ± 4.7% vs. - 27.9 ± 4.5%, P < 0.01) were more altered after aRSA with BFR compared to without BFR. The exercise-induced increase in corticospinal excitability was significantly lower in hypoxic vs. normoxic conditions (e.g., BB motor evoked potential at 75% of MVC: - 2.4 ± 4.2% vs. + 16.0 ± 5.9%, respectively, P = 0.03). CONCLUSION: BFR and hypoxia led to comparable aRSA performance impairments but with distinct fatigue etiology. BFR impaired the muscle excitation-contraction coupling whereas hypoxia predominantly affected corticospinal excitability indicating incapacity of the corticospinal pathway to adapt to fatigue as in normoxia.

Physiological Evaluation for Endurance Exercise Prescription in Sickle Cell Disease.

PURPOSE: Although strenuous exercise may expose sickle cell disease (SCD) patients to risks of vaso-occlusive crisis, evidence suggests that regular endurance exercise may be beneficial. This study aimed to test (i) the safety and usefulness of a submaximal incremental exercise in evaluating physical ability of SCD patients and identify a marker for the management of endurance exercise and (ii) the feasibility of endurance exercise sessions in SCD patients. METHODS: Twenty adults with SCD (12 men and 8 women) performed a submaximal incremental exercise used to determine the first lactate threshold (LT1) and stopped as soon as blood lactate concentration ([lactate]b) reached ≥4 mmol·L. Fifteen of those patients (8 men and 7 women) also performed three 30-min endurance exercise sessions at ~2.5 mmol·L of [lactate]b on separate occasions. RESULTS: LT1 occurred at 47 ± 3 and 33 ± 3 W for men and women, respectively, demonstrating the extreme deconditioning and, thus, low physical ability of adult SCD patients. During endurance exercise, peripheral oxygen saturation and [lactate]b most often remained stable and within acceptable ranges. CONCLUSIONS: The proposed strategy of submaximal incremental exercise allowed safe determination of LT1, an important parameter of patients' physical ability. The study also demonstrated the feasibility and safety of individually tailored endurance exercises at ~2.5 mmol·L of [lactate]b. These latter results suggest that endurance training programs may be considered for adult SCD patients and that the method proposed here may be helpful in that regard.

Faster V̇O2 kinetics after priming exercises of different duration but same fatigue.

This study compared the responses of two priming exercises of similar fatigue on the adjustment of the oxygen uptake time constant (τV̇O2) in cycling. Ten healthy young adults (25 ± 3 yr) performed: three step transitions from a 20-W baseline to the power output (PO) below the gas exchange threshold (MOD, MODPRE); a 3-min bout (P3MIN) at 90% of peak PO (POpeak), followed by MOD (MOD3MIN); and a 6-min bout (P6MIN) at 80% of POpeak, followed by MOD (MOD6MIN). The O2 supply-to-O2 demand ([HHb]/V̇O2) ratio was calculated for MODPRE, MOD3MIN, and MOD6MIN. Neuromuscular fatigue was measured isometrically pre- and post-priming exercise. Reductions in maximal voluntary contraction (-29 ± 6 vs -34 ± 7%) and high-frequency doublet amplitude (-48 ± 13 vs -43 ± 11%) were not significantly different between P3MIN vs P6MIN, suggesting similar fatigue. τV̇O2 for MOD3MIN and MOD6MIN were similar, being ~25% smaller than MODPRE. The [HHb]/V̇O2 ratio was significantly greater in MODPRE (1.13 ± 0.12) compared to MOD3MIN (1.02 ± 0.04) and MOD6MIN (1.02 ± 0.04). This study showed that priming exercise of shorter duration and higher intensity, was sufficient to accelerate V̇O2 kinetics similarly to that observed subsequent to P6MIN when the muscle fatigue was similar.

The relationship between oxygen uptake kinetics and neuromuscular fatigue in high-intensity cycling exercise.

PURPOSE: In theory, a slow oxygen uptake ([Formula: see text]) kinetics leads to a greater accumulation of anaerobic by-products, which can, in turn, induce more neuromuscular fatigue. However, the existence of this relationship has never been tested. METHODS: After two sessions to measure peak [Formula: see text], peak power output (POpeak), and [Formula: see text] kinetics responses in the unfatigued state (τ [Formula: see text] MOD), 10 healthy young adults performed a 6-min cycling bout at 80% POpeak (INT6-min). [Formula: see text] kinetics responses were also measured during INT6-min. Neuromuscular fatigue was measured isometrically pre- and post-INT6-min (immediately post- and 15-s post-INT6-min) with an innovative cycle ergometer. RESULTS: Maximal voluntary contraction (MVC) force, high-frequency doublet amplitude, and the ratio of low- to high-frequency doublet amplitudes decreased by 34 ± 7, 43 ± 11, and 31 ± 13%, respectively (all P < 0.01). A significant Spearman's rank correlation was observed between the change in low-frequency doublet force (ΔDb10) immediately after INT6-min and both τ [Formula: see text] MOD and τ [Formula: see text] INT6-min (ρ = -0.68 and ρ = -0.67, both P < 0.05). When considering the largest responses from the two neuromuscular evaluations post-INT6-min, significant correlations were also found between τ [Formula: see text] MOD and ΔDb10 (ρ = -0.74; P < 0.05) and between τ[Formula: see text] INT6-min and both ΔDb10 and low-frequency fatigue (ρ = -0.70 and ρ = -0.66; both P < 0.05). CONCLUSION: The present results suggest that subjects with slow [Formula: see text] kinetics experience more peripheral fatigue, in particular more excitation-contraction coupling failure, likely due to a greater accumulation of protons and/or inorganic phosphates.

Anticipation of magnetic and electrical stimuli does not impair maximal voluntary force production.

INTRODUCTION: Knowing electro-myostimulation (EMS) will be delivered during a maximal voluntary contraction (MVC) has been demonstrated to limit maximal force production in the knee extensors. Many recent studies instead deliver peripheral nerve stimulation (PNS) or transcranial magnetic stimulation (TMS) during MVCs to assess neuromuscular function. This study investigated the effects of EMS, PNS and TMS on maximal voluntary force production and muscle activation in the knee extensors. METHODS: Nineteen healthy participants performed MVCs under 8 randomized conditions: no stimulation, TMS at 40% of maximal stimulator output, TMS at 70% of maximal stimulator output, single-pulse PNS, paired (100-Hz)-pulse PNS, single-pulse EMS and two conditions where subjects expected TMS at 70% of maximal stimulator output or paired-pulse PNS yet no stimulus was delivered. Knee extensor force, discomfort associated with the stimulus and vastus lateralis, rectus femoris and biceps femoris electromyography (EMG) were recorded. RESULTS: There were no differences between MVC forces and maximal agonist and antagonist muscle activity between conditions. Discomfort was greatest for EMS and least for TMS. CONCLUSION: This study demonstrates that in familiarized subjects, knowing a stimulus (EMS, PNS or TMS) will occur does not impair maximal force or EMG produced despite differences in discomfort associated with the stimulus modalities. These techniques can be used to investigate central drive and peripheral function, at least for intensities comparable to those employed in the present study.

Cerebral and Muscle Oxygenation During Intermittent Hypoxia Exposure in Healthy Humans.

STUDY OBJECTIVES: To evaluate changes in muscle and cerebral oxygenation during intermittent hypoxia (IH). METHODS: Fifteen healthy subjects were exposed to 45-min IH (2-min cycles). Arterial blood oxygen saturation (SpO2), prefrontal cortex and brachial biceps muscle oxygenation (assessed by near-infrared spectroscopy), heart rate, and ventilation were continuously recorded. RESULTS: During 2-min IH cycles, changes in SpO2 (9.2% ± 3.3%) were associated with significant changes in cortex oxygenation (3.2% ± 1.8%), minute ventilation, and heart rate, but no change in muscle oxygenation (0.2% ± 1.0%). CONCLUSIONS: Fluctuations of blood oxygen levels comparable to severe obstructive sleep apnea translate into distinct pattern of oxygenation changes in the muscle and cortex.