Recovery following exercise-induced fatigue: Influence of a single heart rate clamped cycling session under systemic hypoxia.

We investigated whether a single heart rate clamped cycling session under systemic hypoxia affects the recovery of physical and psycho-physiological responses from residual fatigue compared to normoxia. On separate occasions, twelve trained males performed a 3-d acute training camp scenario. On days 1 and 3, participants cycled for 60 min at a constant heart rate (80% of ventilatory threshold). On day 2, fatigue was induced through a simulated team game circuit (STGC), followed by a 60-min intervention of either: (1) heart rate clamped cycling in normoxia; (2) heart rate clamped cycling in hypoxia (simulated altitude ~ 3500 m); or (3) no cycling. Countermovement jump height and leg stiffness were assessed before and after every session. Perceptual fatigue was evaluated daily. Compared to baseline, jump height decreased at all timepoints following the STGC (all p < 0.05). Leg stiffness and cycling power output only decreased immediately following the STGC, with a 48% further decrease in cycling power output in hypoxia compared to normoxia (p < 0.05). Perceived fatigue, decreased sleep quality, and increased muscle soreness responses occurred on day 3 (p < 0.05). A single heart rate-clamped cycling session in hypoxia reduced mechanical output without affecting recovery of physical performance and perceptual measures from residual fatigue induced through team sport activity.

Maintenance of internal load despite a stepwise reduction in external load during moderate intensity heart rate clamped cycling with acute graded normobaric hypoxia in males.

OBJECTIVES: To investigate the acute effects of graded hypoxia on external and internal loads during 60 min of endurance cycling at a clamped heart rate. DESIGN: Repeated measures. METHODS: On separate visits, 16 trained males cycled for 60 min at a clamped heart rate corresponding to 80 % of their first ventilatory threshold at sea-level and 2500 m, 3000 m, 3500 m and 4000 m simulated altitudes (inspired oxygen fractions of 20.9 %, 15.4 %, 14.5 %, 13.6 % and 12.7 %, respectively). Markers of external (power output) and internal (blood lactate concentration, tissue saturation index, cardio-respiratory and perceptual responses) loads were measured every 15 min during cycling. Neuromuscular function of knee extensors was characterised pre- and post-exercise. RESULTS: Compared to sea-level (101 ±â€¯22 W), there was a stepwise reduction in power output with increasing hypoxia severity (-17.9 ±â€¯8.9 %, -27.1 ±â€¯10.7 %, -34.2 ±â€¯12.0 % and - 44.6 ±â€¯15.1 % at 2500 m, 3000 m, 3500 m, and 4000 m, respectively, all p < 0.05). Blood lactate and tissue saturation index were not different across hypoxia severities, and perceptual responses were exacerbated at 4000 m only, with increased breathing difficulty. Knee extensor torque decreased post-exercise (-14.5 ±â€¯9.0 %, p < 0.05), independent of condition. CONCLUSIONS: Increasing hypoxia severity reduces cycling power output and arterial oxygen saturation in a stepwise fashion without affecting exercise responses between sea-level and simulated altitudes up to 3500 m despite breathing difficulty being elevated at 4000 m.

Exercise responses to heart rate clamped cycling with graded blood flow restriction.

OBJECTIVES: To quantify the acute effects of graded blood flow restriction on the interaction between changes in mechanical output, muscle oxygenation trends and perceptual responses to heart rate clamped cycling. DESIGN: Repeated measures. METHODS: Twenty-five adults (21 men) performed six, 6-min cycling bouts (24 min of recovery) at a clamped heart rate corresponding to their first ventilatory threshold at 0 % (unrestricted), 15 %, 30 %, 45 %, 60 % and 75 % of arterial occlusion pressure with the cuffs inflated bilaterally from the fourth to the sixth minute. Power output, arterial oxygen saturation (pulse oximetry) and vastus lateralis muscle oxygenation (near-infrared spectroscopy) were monitored during the final 3 min of pedalling, whilst perceptual responses (modified Borg CR10 scales) were obtained immediately after exercise. RESULTS: Compared to unrestricted cycling, average power output for minutes 4-6 decreased exponentially for cuff pressures ranging 45-75 % of arterial occlusion pressure (P < 0.001). Peripheral oxygen saturation averaged ∼96 % across all cuff pressures (P = 0.318). Deoxyhemoglobin changes were larger at 45-75 % versus 0 % of arterial occlusion pressure (P < 0.05), whereas higher total haemoglobin values occurred at 60-75 % of arterial occlusion pressure (P < 0.05). Sense of effort, ratings of perceived exertion, pain from cuff pressure, and limb discomfort were exaggerated at 60-75 % versus 0 % of arterial occlusion pressure (P < 0.001). CONCLUSIONS: Blood flow restriction of at least 45 % of arterial occlusion pressure is required to reduce mechanical output during heart rate clamped cycling at the first ventilatory threshold. Whilst power decreases non-linearly above this pressure threshold, higher occlusion levels ranging 60-75 % of arterial occlusion pressure also accentuate muscle deoxygenation and exercise-related sensations.

Detecting mechanical breakpoints during treadmill-based graded exercise test: Relationships to ventilatory thresholds.

BACKGROUND: While changes in cardio-respiratory variables during graded exercise tests (GXTs) are well described, less is known about running mechanical alterations. PURPOSE: We determined mechanical breakpoints during GXT and compared their temporal location with thresholds in ventilation. METHODS: Thirty-one recreational male runners completed continuous GXT on an instrumented treadmill, starting at 2.5 m.s-1 with velocity increases of +0.14 m.s-1 every 30 s. Subsequently, the first and second ventilatory thresholds (VT1 and VT2) were determined from expired gases. Spatio-temporal and antero-posterior force variables, and spring-mass model characteristics were averaged for each stage. Mechanical breakpoints were detected using a linear fit process that partitioned the timeseries into two regions and minimised the error sum of squares. All measurements were normalised to % GXT duration for subsequent comparisons. RESULTS: Fifteen out of 16 mechanical variables (all except leg stiffness) displayed breakpoints occurring between 61.9% and 82.3% of GXT duration; these occurred significantly later than VT1 (46.9 ± 6.4% of GXT duration, p < .05). Mechanical breakpoints for eight variables (step frequency, aerial time, step length, peak push-off force, braking impulse, peak vertical force, maximal downward vertical displacement and leg compression) occurred at a time point not different to VT2 (75.3 ± 6.2% of GXT duration; all p > .05). Relationships between mechanical breakpoints and either VT1 or VT2 were weak (all r < 0.25). CONCLUSION: During treadmill GXT, breakpoints can be detected for the vast majority of mechanical variables (except leg stiffness), yet these are not related with ventilatory thresholds.

Constant low-to-moderate mechanical asymmetries during a treadmill graded exercise test.

This study describes asymmetry in key mechanical variables during a treadmill-based, running graded exercise test (GXT). Twenty-one recreationally trained male runners completed a continuous, maximal GXT on an instrumented treadmill, starting at 9 km.h-1 with speed increases of +0.5 km.h-1 every 30 s, for the determination of ventilatory threshold (VT), respiratory compensation point (RCP), and maximal oxygen uptake (MAX). Ground reaction forces were recorded continuously and subsequently averaged from 10 consecutive steps corresponding to VT, RCP and MAX intensity stages (13.4 ± 1.2 km.h-1, 16.0 ± 1.6 km.h-1 and 18.2 ± 1.5 km.h-1, respectively). Asymmetry scores were assessed from the "symmetry angle" (SA) formulae, where a score of 0%/100% indicates perfect symmetry/asymmetry; these were then compared between the three intensity stages. There was no influence of exercise intensity on SA scores for any of the sixteen biomechanical variables (P > 0.222). The group mean SA scores did not exceed 1.5% for spatio-temporal variables (contact time, aerial time, frequency and step length). There were larger mean SA scores for mean loading rate (3.7 ± 2.7%) and most spring-mass model variables (vertical stiffness: 2.2 ± 1.6% and leg stiffness: 1.7 ± 1.4%). The SA scores were ∼1.0-3.5% for braking and propulsive phase durations, peak forces, and resulting impulses. Lower extremities behave similarly at submaximal and maximal intensities during GXT, indicating that runners maintained relatively even strides as intensity increased. However, practitioners must be careful not to infer the presence of asymmetry during GXT based on a single variable, given the lower SA scores for spatio-temporal parameters.Highlights Our comprehensive list of sixteen mechanical variables provides a mechanical norm of expected asymmetry during treadmill graded exercise testing for recreationally trained runners.The stride pattern across submaximal and maximal exercise intensities remains consistent between limbs, with mechanical asymmetries being more individual-specific than intensity stage-dependent.Low to moderate asymmetry is a natural phenomenon in recreationally trained runners during treadmill graded exercise testing; notwithstanding, asymmetry scores appear inconsistent between mechanical parameters.

Gait asymmetries during perceptually-regulated interval running in hypoxia and normoxia.

This study aimed to characterise bilateral asymmetry in running mechanics during perceptually regulated, high-intensity intermittent running in hypoxia and normoxia and examines whether inter-limb differences in running mechanics are modified between and within intervals. Nineteen trained runners completed 4 × 4-min treadmill running bouts (3-min passive recoveries) at a perceived rating exertion of 16 on the 6-20 Borg scale in either hypoxic (FiO2 = 0.15) or normoxic (FiO2 = 0.21) conditions. Ground reaction force recordings at constant velocity (group average: 14.8 ± 1.9 km/h) allowed measurement of running kinetics/kinematics and calculation of spring-mass model characteristics at the beginning and the end of each 4-min interval. Lower limb asymmetry was assessed from the 'symmetry angle' (SA) score. There were no between intervals (P > 0.087), within intervals (P > 0.076) or FiO2 (P > 0.128) differences in SA scores for any of the 16 biomechanical variables. Mean SA scores were lower than 1.5% for spatio-temporal variables, ~1.5-3% for braking and push-off phase durations, peak forces and impulses and ~4-6% for mean loading rate and vertical stiffness. With preserved lower limb asymmetries both between and within intervals and with additional hypoxia, trained runners completing perceptually regulated interval treadmill runs may anticipate a maintained performance without heightened injury risk.

Running mechanics adjustments to perceptually-regulated interval runs in hypoxia and normoxia.

OBJECTIVES: We determined whether perceptually-regulated, high-intensity intermittent runs in hypoxia and normoxia induce similar running mechanics adjustments within and between intervals. DESIGN: Within-participants repeated measures. METHODS: Nineteen trained runners completed a high-intensity intermittent running protocol (4×4-min intervals at a perceived rating exertion of 16 on the 6-20 Borg scale, 3-min passive recoveries) in either hypoxic (FiO2=0.15) or normoxic (FiO2=0.21) conditions. Running mechanics were collected over 10 consecutive steps, at constant velocity (∼15.0±2.0km.h-1), at the beginning and the end of each 4-min interval. Repeated measure ANOVA were used to assess within intervals (onset vs. end of each interval), between intervals (interval 1, 2, 3 vs. 4) and FiO2 (0.15 vs. 0.21) main effects and any potential interaction. RESULTS: Participants progressively reduced running velocity from interval 1-4, and more so in hypoxia compared to normoxia for intervals 2, 3 and 4 (P<0.01). There were no between intervals (across all intervals P>0.298) and FiO2 (across all intervals P>0.082) main effects or any significant between intervals×within intervals×FiO2 interactions (all P>0.098) for any running mechanics variables. Irrespective of interval number or FiO2, peak loading rate (+10.6±7.7%; P<0.001) and duration of push-off phase (+2.0±3.1%; P=0.001) increased from the onset to the end of 4-min intervals, whereas peak push-off force decreased (-4.0±4.0%; P<0.001). CONCLUSIONS: When carrying out perceptually-regulated interval treadmill runs, runners adjust to progressively slower velocities in hypoxia compared to normoxia. However, only subtle constant-velocity modifications of their mechanical behaviour occurred within each set, independently of FiO2 or interval number.