Combined Temperature and Altitude Challenges do not Exacerbate the Degree of Muscle Fatigue Despite Shorter Cycling Time to Exhaustion

Fulco, Charles S., Steven F. Lewis, Peter N. Frykman, Robert Boushel, Sinclair Smith, Everett A. Harman, Allen Cymerman, and Kent B. Pandolf. Muscle fatigue and exhaustion during dynamic leg exercise in normoxia and hypobaric hypoxia. J. Appl. Physiol. 81(5): 1891–1900, 1996.—Using an exercise device that integrates maximal voluntary static contraction (MVC) of knee extensor muscles with dynamic knee extension, we compared progressive muscle fatigue, i.e., rate of decline in force-generating capacity, in normoxia (758 Torr) and hypobaric hypoxia (464 Torr). Eight healthy men performed exhaustive constant work rate knee extension (21 ± 3 W, 79 ± 2 and 87 ± 2% of 1-leg knee extension O2 peak uptake for normoxia and hypobaria, respectively) from knee angles of 90–150° at a rate of 1 Hz. MVC (90° knee angle) was performed before dynamic exercise and during ≤5-s pauses every 2 min of dynamic exercise. MVC force was 578 ± 29 N in normoxia and 569 ± 29 N in hypobaria before exercise and fell, at exhaustion, to similar levels (265 ± 10 and 284 ± 20 N for normoxia and hypobaria, respectively; P > 0.05) that were higher ( P < 0.01) than peak force of constant work rate knee extension (98 ± 10 N, 18 ± 3% of MVC). Time to exhaustion was 56% shorter for hypobaria than for normoxia (19 ± 5 vs. 43 ± 7 min, respectively; P < 0.01), and rate of right leg MVC fall was nearly twofold greater for hypobaria than for normoxia (mean slope = −22.3 vs. −11.9 N/min, respectively; P < 0.05). With increasing duration of dynamic exercise for normoxia and hypobaria, integrated electromyographic activity during MVC fell progressively with MVC force, implying attenuated maximal muscle excitation. Exhaustion, per se, was postulated to relate more closely to impaired shortening velocity than to failure of force-generating capacity.

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Pacing Strategy, Muscle Fatigue, and Technique in 1500-m Speed-Skating and Cycling Time Trials

International Journal of Sports Physiology and Performance ◽

10.1123/ijspp.2014-0603 ◽

2016 ◽

Vol 11 (3) ◽

pp. 337-343 ◽

Cited By ~ 27

Author(s):

Inge K. Stoter ◽

Brian R. MacIntosh ◽

Jared R. Fletcher ◽

Spencer Pootz ◽

Inge Zijdewind ◽

...

Keyword(s):

Muscle Fatigue ◽

Blood Lactate ◽

National Level ◽

Time Trial ◽

Voluntary Activation ◽

Slow Start ◽

Speed Skating ◽

Fast Start ◽

Start Trial ◽

Cycling Time

Purpose:To evaluate pacing behavior and peripheral and central contributions to muscle fatigue in 1500-m speed-skating and cycling time trials when a faster or slower start is instructed.Methods:Nine speed skaters and 9 cyclists, all competing at regional or national level, performed two 1500-m time trials in their sport. Athletes were instructed to start faster than usual in 1 trial and slower in the other. Mean velocity was measured per 100 m. Blood lactate concentrations were measured. Maximal voluntary contraction (MVC), voluntary activation (VA), and potentiated twitch (PT) of the quadriceps muscles were measured to estimate central and peripheral contributions to muscle fatigue. In speed skating, knee, hip, and trunk angles were measured to evaluate technique.Results:Cyclists showed a more explosive start than speed skaters in the fast-start time trial (cyclists performed first 300 m in 24.70 ± 1.73 s, speed skaters in 26.18 ± 0.79 s). Both trials resulted in reduced MVC (12.0% ± 14.5%), VA (2.4% ± 5.0%), and PT (25.4% ± 15.2%). Blood lactate concentrations after the time trial and the decrease in PT were greater in the fast-start than in the slow-start trial. Speed skaters showed higher trunk angles in the fast-start than in the slow-start trial, while knee angles remained similar.Conclusions:Despite similar instructions, behavioral adaptations in pacing differed between the 2 sports, resulting in equal central and peripheral contributions to muscle fatigue in both sports. This provides evidence for the importance of neurophysiological aspects in the regulation of pacing. It also stresses the notion that optimal pacing needs to be studied sport specifically, and coaches should be aware of this.

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Pre-exercise Carbohydrate Drink Adding Protein Improves Post-exercise Fatigue Recovery

Frontiers in Physiology ◽

10.3389/fphys.2021.765473 ◽

2021 ◽

Vol 12 ◽

Author(s):

Albert Yi-Wey Tan ◽

Sareena-Hanim Hamzah ◽

Chih-Yang Huang ◽

Chia-Hua Kuo

Keyword(s):

G Protein ◽

Endurance Performance ◽

Nitrogen Sources ◽

Time To Exhaustion ◽

Antioxidant Power ◽

Post Exercise ◽

Dietary Nitrogen ◽

Exercise Fatigue ◽

Fatigue Recovery ◽

Cycling Time

Purpose: This study aimed to assess the requirement of protein in pre-exercise carbohydrate drinks for optimal endurance performance at high intensity and post-exercise fatigue recovery.Methods: Endurance performance at 85% V.⁢O2peak of young men (age 20 ± 0.9 years, V.⁢2peak 49.3 ± 0.3 L/min) was measured for two consecutive days using cycling time to exhaustion and total work exerted 2 h after three isocaloric supplementations: RICE (50 g, protein: 1.8 g), n = 7; SOY + RICE (50 g, protein: 4.8 g), n = 7; and WHEY + RICE (50 g, protein: 9.2 g), n = 7.Results: Endurance performance was similar for the three supplemented conditions. Nevertheless, maximal cycling time and total exerted work from Day 1 to Day 2 were improved in the WHEY + RICE (+21%, p = 0.05) and SOY-RICE (+16%, p = 0.10) supplemented conditions, not the RICE supplemented condition. Increases in plasma interleukin-6 (IL-6) were observed 1 h after exercise regardless of supplemented conditions. Plasma creatine kinase remained unchanged after exercise for all three supplemented conditions. Increases in ferric reducing antioxidant power (FRAP) after exercise were small and similar for the three supplemented conditions.Conclusion: Adding protein into carbohydrate drinks provides no immediate benefit in endurance performance and antioxidant capacity yet enhances fatigue recovery for the next day. Soy-containing carbohydrate drink, despite 50% less protein content, shows similar fatigue recovery efficacy to the whey protein-containing carbohydrate drink. These results suggest the importance of dietary nitrogen sources in fatigue recovery after exercise.

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Reproducibility of the Cycling Time to Exhaustion at in Highly Trained Cyclists

Canadian Journal of Applied Physiology ◽

10.1139/h03-046 ◽

2003 ◽

Vol 28 (4) ◽

pp. 605-615 ◽

Cited By ~ 8

Author(s):

Paul B. Laursen ◽

Cecilia M. Shing ◽

David G. Jenkins

Keyword(s):

Aerobic Power ◽

Cycling Performance ◽

Peak Oxygen Uptake ◽

Time To Exhaustion ◽

Subject Variability ◽

Progressive Exercise ◽

Two Measures ◽

The Mean ◽

Cycling Time ◽

Within Subject Variability

The purpose of the present study was to examine, in highly trained cyclists, the reproducibility of cycling time to exhaustion (Tmax) at the power output equal to that attained at peak oxygen uptake ([Formula: see text]) during a progressive exercise test. Forty-three highly trained male cyclists (M ± SD; age = 25 + 6 yrs; weight = 75 ± 7 kg; [Formula: see text] = 64.8 ± 5.2 mlùkg−1•min−1) performed two Tmax tests one week apart. While the two measures of Tmax were strongly related (r = 0.884; p < 0.001), Tmax from the second test (245 ± 57 s) was significantly higher than that of the first (237 ± 57 s; p = 0.047; two-tailed). Within-subject variability in the present study was calculated to be 6 ± 6%, which was lower than that previously reported for Tmax in sub-elite runners (25%). The mean Tmax was significantly (p < 0.05) related to both the second ventilatory turnpoint (VT2; r = 0.38) and to [Formula: see text] (r = 0.34). Despite a relatively low within-subject coefficient of variation, these data demonstrate that the second score in a series of two Tmax tests may be significantly greater than the first. Moreover, the present data show that Tmax in highly trained cyclists is moderately related to VT2 and [Formula: see text]Key words: maximal aerobic power, endurance, fatigue, anaerobic threshold, cycling performance

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Combining heat stress and moderate hypoxia reduces cycling time to exhaustion without modifying neuromuscular fatigue characteristics

European Journal of Applied Physiology ◽

10.1007/s00421-014-2883-0 ◽

2014 ◽

Vol 114 (7) ◽

pp. 1521-1532 ◽

Cited By ~ 21

Author(s):

Olivier Girard ◽

Sébastien Racinais

Keyword(s):

Heat Stress ◽

Neuromuscular Fatigue ◽

Time To Exhaustion ◽

Moderate Hypoxia ◽

Fatigue Characteristics ◽

Cycling Time

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Locomotor muscle fatigue increases cardiorespiratory responses and reduces performance during intense cycling exercise independently from metabolic stress

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00678.2007 ◽

2008 ◽

Vol 294 (3) ◽

pp. R874-R883 ◽

Cited By ~ 129

Author(s):

Samuele M. Marcora ◽

Andrea Bosio ◽

Helma M. de Morree

Keyword(s):

Muscle Fatigue ◽

Exercise Performance ◽

High Intensity ◽

Perceived Exertion ◽

Metabolic Stress ◽

Motor Command ◽

Time To Exhaustion ◽

Test Duration ◽

Cardiorespiratory Responses ◽

Locomotor Muscles

Locomotor muscle fatigue, defined as an exercise-induced reduction in maximal voluntary force, occurs during prolonged exercise, but its effects on cardiorespiratory responses and exercise performance are unknown. In this investigation, a significant reduction in locomotor muscle force (−18%, P < 0.05) was isolated from the metabolic stress usually associated with fatiguing exercise using a 100-drop-jumps protocol consisting of one jump every 20 s from a 40-cm-high platform. The effect of this treatment on time to exhaustion during high-intensity constant-power cycling was measured in study 1 ( n = 10). In study 2 ( n = 14), test duration (871 ± 280 s) was matched between fatigue and control condition (rest). In study 1, locomotor muscle fatigue caused a significant curtailment in time to exhaustion (636 ± 278 s) compared with control (750 ± 281 s) ( P = 0.003) and increased cardiac output. Breathing frequency was significantly higher in the fatigue condition in both studies despite similar oxygen consumption and blood lactate accumulation. In study 2, high-intensity cycling did not induce further fatigue to eccentrically-fatigued locomotor muscles. In both studies, there was a significant increase in heart rate in the fatigue condition, and perceived exertion was significantly increased in study 2 compared with control. These results suggest that locomotor muscle fatigue has a significant influence on cardiorespiratory responses and exercise performance during high-intensity cycling independently from metabolic stress. These effects seem to be mediated by the increased central motor command and perception of effort required to exercise with weaker locomotor muscles.

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On the Implication of Dietary Nitrate Supplementation for the Hemodynamic and Fatigue Response to Cycling Exercise

Journal of Applied Physiology ◽

10.1152/japplphysiol.00400.2021 ◽

2021 ◽

Author(s):

Taylor S. Thurston ◽

Joshua C. Weavil ◽

Thomas J. Hureau ◽

Jayson R. Gifford ◽

Vincent P. Georgescu ◽

...

Keyword(s):

Muscle Fatigue ◽

Femoral Nerve ◽

Voluntary Activation ◽

Peak Power Output ◽

Cycling Exercise ◽

Dietary Nitrate ◽

Task Failure ◽

Nitrate Supplementation ◽

The Impact ◽

Cycling Time

This study investigated the impact of dietary nitrate supplementation on peripheral hemodynamics, the development of neuromuscular fatigue, and time to task failure during cycling exercise. Eleven recreationally active male participants (27±5 years, VO2max: 42±2ml/kg/min) performed two experimental trials following 3 days of either dietary nitrate-rich beetroot juice (4.1mmol NO3-/day; DNS) or placebo (PLA) supplementation in a blinded, counterbalanced order. Exercise consisted of constant-load cycling at 50, 75, and 100 W (4-min each) and, at ~80% of peak power output (218±12W), to task-failure. All participants returned to repeat the shorter of the two trials performed to task-failure, but with the opposite supplementation regime (ISO-time comparison). Mean arterial pressure (MAP), leg blood flow (QL; Doppler ultrasound), leg vascular conductance (LVC), and pulmonary gas exchange were continuously assessed during exercise. Locomotor muscle fatigue was determined by the change in pre- to post-exercise quadriceps twitch-torque (∆Qtw) and voluntary activation (∆VA; electrical femoral nerve stimulation). Following DNS, plasma [nitrate] (~670 vs ~180 nmol) and [nitrite] (~775 vs ~11 nmol) were significantly elevated compared to PLA. Unlike PLA, DNS lowered both QL and MAP by ~8% (P<0.05), but did not alter LVC (P=0.31). VO2 across work rates, as well as cycling time to task-failure (~7min) and locomotor muscle fatigue following the ISO-time comparison were not different between the two conditions (∆Qtw ~42%, ∆VA ~4%). Thus, despite significant hemodynamic changes, DNS did not alter the development of locomotor muscle fatigue and, ultimately, cycling time to task failure.

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Exercise-induced respiratory muscle fatigue: implications for performance

Journal of Applied Physiology ◽

10.1152/japplphysiol.01157.2007 ◽

2008 ◽

Vol 104 (3) ◽

pp. 879-888 ◽

Cited By ~ 134

Author(s):

Lee M. Romer ◽

Michael I. Polkey

Keyword(s):

Blood Flow ◽

Muscle Fatigue ◽

Respiratory System ◽

Exercise Tolerance ◽

Respiratory Muscle ◽

Respiratory Muscles ◽

Time To Exhaustion ◽

Respiratory Muscle Fatigue ◽

Objective Evidence ◽

Exercise Induced

It is commonly held that the respiratory system has ample capacity relative to the demand for maximal O2and CO2transport in healthy humans exercising near sea level. However, this situation may not apply during heavy-intensity, sustained exercise where exercise may encroach on the capacity of the respiratory system. Nerve stimulation techniques have provided objective evidence that the diaphragm and abdominal muscles are susceptible to fatigue with heavy, sustained exercise. The fatigue appears to be due to elevated levels of respiratory muscle work combined with an increased competition for blood flow with limb locomotor muscles. When respiratory muscles are prefatigued using voluntary respiratory maneuvers, time to exhaustion during subsequent exercise is decreased. Partially unloading the respiratory muscles during heavy exercise using low-density gas mixtures or mechanical ventilation can prevent exercise-induced diaphragm fatigue and increase exercise time to exhaustion. Collectively, these findings suggest that respiratory muscle fatigue may be involved in limiting exercise tolerance or that other factors, including alterations in the sensation of dyspnea or mechanical load, may be important. The major consequence of respiratory muscle fatigue is an increased sympathetic vasoconstrictor outflow to working skeletal muscle through a respiratory muscle metaboreflex, thereby reducing limb blood flow and increasing the severity of exercise-induced locomotor muscle fatigue. An increase in limb locomotor muscle fatigue may play a pivotal role in determining exercise tolerance through a direct effect on muscle force output and a feedback effect on effort perception, causing reduced motor output to the working limb muscles.

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Endurance and Resistance Respiratory Muscle Training and Aerobic Exercise Performance in Hypobaric Hypoxia

Aerospace Medicine and Human Performance ◽

10.3357/amhp.5624.2020 ◽

2020 ◽

Vol 91 (10) ◽

pp. 776-784

Author(s):

Courtney E. Wheelock ◽

Hayden W. Hess ◽

Blair D. Johnson ◽

Zachary J. Schlader ◽

Brian M. Clemency ◽

...

Keyword(s):

Pulmonary Function ◽

Aerobic Exercise ◽

Muscle Fatigue ◽

Exercise Performance ◽

Hypobaric Hypoxia ◽

Respiratory Muscle ◽

Respiratory Muscle Training ◽

Time To Exhaustion ◽

Muscle Training ◽

Before And After

INTRODUCTION: Hypoxia-induced hyperventilation is an effect of acute altitude exposure, which may lead to respiratory muscle fatigue and secondary locomotor muscle fatigue. The purpose of this study was to determine if resistive and/or endurance respiratory muscle training (RRMT and ERMT, respectively) vs. placebo respiratory muscle training (PRMT) improve cycling performance at altitude.METHODS: There were 24 subjects who were assigned to PRMT (N 8), RRMT (N 8), or ERMT (N 8). Subjects cycled to exhaustion in a hypobaric chamber decompressed to 3657 m (12,000 ft) at an intensity of 55% sea level maximal oxygen consumption (Vo2max) before and after respiratory muscle training (RMT). Additionally, subjects completed a Vo2max, pulmonary function, and respiratory endurance test (RET) before and after RMT. All RMT protocols consisted of three 30-min training sessions per week for 4 wk.RESULTS: The RRMT group increased maximum inspiratory (PImax) and expiratory (PEmax) mouth pressure after RMT (PImax: 117.7 11.6 vs. 162.6 20.0; PEmax: 164.0 33.2 vs. 216.5 44.1 cmH2O). The ERMT group increased RET after RMT (5.2 5.2 vs.18.6 16.9 min). RMT did not improve Vo2max in any group. Both RRMT and ERMT groups increased cycling time to exhaustion (RRMT: 35.9 17.2 vs. 45.6 22.2 min and ERMT: 33.8 9.6 vs. 42.9 27.0 min).CONCLUSION: Despite different improvements in pulmonary function, 4 wk of RRMT and ERMT both improved cycle time to exhaustion at altitude.Wheelock CE, Hess HW, Johnson BD, Schlader ZJ, Clemency BM, St. James E, Hostler D. Endurance and resistance respiratory muscle training and aerobic exercise performance in hypobaric hypoxia. Aerosp Med Hum Perform. 2020; 91(10):776784.

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