Rationale: Normoxic heliox (mixture of 79% He and 21% O2) may enhance exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). It remains to be determined whether part of these beneficial effects could be ascribed to increased O2 delivery (O2DEL) to locomotor muscles. Objectives: To investigate the effects of heliox on peripheral O2DEL and utilization during exercise in moderate to severe COPD. Methods: Twelve mildly hypoxic or nonhypoxemic men (FEV1 = 45.0 ± 13.0% predicted) underwent constant-work rate tests (70–80% peak) to the limit of tolerance while receiving heliox or room air. Near-infrared spectroscopy determined changes (Δ) in leg muscle deoxygenation (deoxyhemoglobin concentration [HHb], an index of fractional O2 extraction), and surface electromyography estimated muscle fiber recruitment (n = 5). Q̇ and SpO2 were monitored by impedance cardiography and pulse oximetry, respectively. Measurements and Main Results: Heliox significantly decreased dynamic hyperinflation and increased exercise tolerance compared with room air (640 ± 95 s vs. 371 ± 100 s; P < 0.01). Heliox also accelerated on-exercise dynamics of Q̇, which were accompanied by faster O2 uptake kinetics and slower Δ[HHb] responses (P < 0.05). During steady-state exercise, SpO2-corrected Δ[HHb] values decreased with heliox despite no significant changes in cardiac output. Muscle fiber recruitment and leg effort scores were also diminished (P < 0.05). On a multiple regression analysis, reductions in dynamic hyperinflation, dyspnea, and Δ[HHb] were independently related to improvements in exercise tolerance with heliox (R2 = 0.91; P < 0.01). Conclusions: Heliox increases lower limb O2DEL and utilization during dynamic exercise in patients with moderate to severe COPD. These effects enhance exercise tolerance in this patient population.

Muscle fatigue may alter kinematics and contribute to repetitive strain injuries. This study quantified how both localized muscle fatigue and movement kinematics change over time during exhaustive cycling. Seven highly trained cyclists rode a stationary bicycle ergometer at 100% of their maximum oxygen consumption ( VO ₂ max) until voluntary exhaustion. Cycling kinematics and electromyography (EMG) activity from select lower extremity muscles were recorded. Cross-correlations were computed to quantify how EMG median frequencies (MDFs) changed with changes in movement kinematics. All athletes maintained both cadence and power output for ~ 90% of the trial duration. Significant sustained muscle fatigue occurred in 18 of 28 muscles tested, most prominently in the biceps femoris ( p = 0.020) and gastrocnemius ( p = 0.018). Kinematics and MDF both fluctuated nonmonotonically as subjects fatigued. Changes in MDF significantly preceded changes in mean trunk lean ( p = 0.009) and hip angles ( p = 0.025), and trunk lean range of motion ( p = 0.029). Fluctuations in MDF were positively correlated with fluctuations in mean trunk lean ( p = 0.009 ) and knee splay angles ( p = 0.011), and with trunk lean ( p = 0.002) and ankle ( p = 0.001) range of motion. These results therefore establish a direct link between changes in muscle fatigue state and subsequent changes in movement kinematics during cycling.

Reaction time and response time are considered important abilities and can potentially affect combat performance. This study investigated the effect of a specific fatigue protocol on reaction time, response time, performance time, and kick impact. Seven male athletes reported to the laboratory on two different days. During day one, athletes performed a specific progressive taekwondo test, and on day two, a protocol for determining reaction time, response time, performance time, and kick impact before and after a time to exhaustion test at an intensity level corresponding to the maximal kick frequency obtained during the specific progressive taekwondo test. Muscle activation from rectus femoris and kick impact of the preferred limb were assessed. No differences were observed for response time and performance time. However, kick impact decreased (43 ± 27 to 13 ± 10 g, p < 0.01) while reaction time increased (145 ± 51 to 223 ± 133 ms, p < 0.05). Moderate correlation was observed between kick impact and response time (r = 0.565; p < 0.01), and kick impact and performance time (r = 0.494; p < 0.05). Results indicate that coaches and athletes may use taekwondo training programmes on coordination-based exercises leading to improve response time and to reduce fatigue effects in order to improve technique effectiveness and enhance the possibilities of scoring in a competitive situation.

Objective: The purpose of this study was to evaluate the effects of light-emitting diodes therapy (LEDT) on quadriceps muscle fatigue by using torque values from the isokinetic dynamometer as an outcome measure. Background Data: Light therapy is considered an innovative way to prevent muscle fatigue. Although positive results have been obtained in animal models and in clinical experiments, no results are available on the effects of this therapeutic modality on human performance studies with isokinetic dynamometry. Materials and Methods: Seventeen healthy and physically active male volunteers were included in a crossover randomized double-blinded placebo-controlled trial. They performed two sessions of an isokinetic fatigue test (30 maximal concentric knee flexion–extension contractions; range of motion, 90 degrees; angular velocity, 180 degrees per second) after LEDT or placebo treatment. Maximal knee extensor muscle isokinetic voluntary contractions were performed before (PRE-MVC) and after (POST-MVC) the fatigue test. LEDT treatment was performed with a multidiode cluster probe (34 red diodes of 660 nm, 10 mW; 35 infrared diodes of 850 nm, 30 mW) at three points of the quadriceps muscle, with a total irradiating dose of 125.1 J. Results: No differences were observed in the PRE-MVC between LEDT (284.81 ± 4.52 Nm) and placebo (282.65 ± 52.64 Nm) treatments. However, for the POST-MVC, higher torques ( p = 0.034) were observed for LEDT (237.68 ± 48.82 Nm) compared with placebo (225.68 ± 44.14 Nm) treatment. Conclusion: LEDT treatment produced a smaller maximal isometric torque decrease after high-intensity concentric isokinetic exercise, which is consistent with an increase in performance.

Technique changes in cyclists are not well described during exhaustive exercise. Therefore the aim of the present study was to analyze pedaling technique during an incremental cycling test to exhaustion. Eleven cyclists performed an incremental cycling test to exhaustion. Pedal force and joint kinematics were acquired during the last three stages of the test (75%, 90% and 100% of the maximal power output). Inverse dynamics was conducted to calculate the net joint moments at the hip, knee and ankle joints. Knee joint had an increased contribution to the total net joint moments with the increase of workload (5–8% increase, p < 0.01). Total average absolute joint moment and knee joint moment increased during the test (25% and 39%, for p < 0.01, respectively). Increases in plantar flexor moment (32%, p < 0.01), knee (54%, p < 0.01) and hip flexor moments (42%, p = 0.02) were found. Higher dorsiflexion (2%, for p = 0.03) and increased range of motion (19%, for p = 0.02) were observed for the ankle joint. The hip joint had an increased flexion angle (2%, for p < 0.01) and a reduced range of motion (3%, for p = 0.04) with the increase of workload. Differences in joint kinetics and kinematics indicate that pedaling technique was affected by the combined fatigue and workload effects.