REPRODUCIBLE MUSCLE PERFORMANCE DURING CONSTANT WORK RATE DYNAMIC LEG EXERCISE

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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PROGRESSIVE QUADRICEPS FEMORIS MUSCLE FATIGUE DURING CONSTANT WORK RATE DYNAMIC EXERCISE

Medicine & Science in Sports & Exercise ◽

10.1249/00005768-199505001-00445 ◽

1995 ◽

Vol 27 (Supplement) ◽

pp. S79

Author(s):

S. F. Lewis ◽

C. S. Fulco ◽

P. Frykman ◽

R. Boushel ◽

S. Smith ◽

...

Keyword(s):

Muscle Fatigue ◽

Quadriceps Femoris ◽

Work Rate ◽

Dynamic Exercise ◽

Quadriceps Femoris Muscle ◽

Constant Work Rate ◽

Rate Dynamic ◽

Femoris Muscle

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Quantitation of progressive muscle fatigue during dynamic leg exercise in humans

Journal of Applied Physiology ◽

10.1152/jappl.1995.79.6.2154 ◽

1995 ◽

Vol 79 (6) ◽

pp. 2154-2162 ◽

Cited By ~ 14

Author(s):

C. S. Fulco ◽

S. F. Lewis ◽

P. N. Frykman ◽

R. Boushel ◽

S. Smith ◽

...

Keyword(s):

Muscle Fatigue ◽

Biceps Femoris ◽

Knee Extension ◽

Quadriceps Femoris ◽

Work Rate ◽

Myoelectric Activity ◽

Work Intensity ◽

O2 Uptake ◽

Constant Work Rate ◽

Leg Exercise

There is virtually no published information on muscle fatigue, defined as a gradual decline in force-generating capacity, during conventional dynamic (D) leg exercise. To quantitate progression of fatigue, we developed 1) a model featuring integration of maximal voluntary static contraction (MVC) of knee extension (KE) muscles with ongoing DKE and 2) a device that allows frequent rapid transfer between DKE isolated to the quadriceps femoris muscles and measurement of KE MVC. Eight healthy men performed graded and submaximal constant work rate one-leg DKE to exhaustion while seated. Work rate, a product of a contraction rate (1 Hz), force measured at the ankle, and distance of ankle movement from 90 degrees to 150 degrees of KE, was precisely controlled. Lack of rise in myoelectric activity in biceps femoris of the active leg during DKE and MVC was consistent with restriction of muscle action to quadriceps femoris. The slope of the linear relationship between O2 uptake and work rate was 13.7 ml O2/W (r = 0.93). This slope and the increase of heart rate relative to increasing work intensity agreed with published values for D leg exercise. Test-retest values for O2 uptake were similar (P > 0.05) for matched DKE work rates. To track fatigue, MVC (90 degrees knee angle) was performed every 2 min of DKE. After 4 min of DKE at work rates corresponding to (mean +/- SE) 66 +/- 2, 78 +/- 2, and 100% of peak DKE O2 uptake, MVC fell to 95 +/- 3, 90 +/- 5, and 65 +/- 7%* of MVC of rested muscle, respectively (*P < 0.01 from previous work rates). Virtually identical declines in MVC were observed by the end of graded work rate DKE and submaximal constant work rate DKE tests. Quantitation of progressive muscle fatigue during D leg exercise provides a framework to study the effects of a variety of interventions on the fatigue process and may permit unique insights into the involved mechanisms.

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Comparative Measurement Properties of Constant Work-Rate Cycling and Endurance Shuttle Walking in Patients with COPD: Data from the TORRACTO Study

Pneumologie ◽

10.1055/s-0037-1619357 ◽

2018 ◽

Vol 72 (S 01) ◽

pp. S90-S90

Author(s):

K Siemon ◽

F Maltais ◽

DE O'Donnell ◽

A Hamilton ◽

Y Zhao ◽

...

Keyword(s):

Work Rate ◽

Measurement Properties ◽

Comparative Measurement ◽

Constant Work Rate

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A Rapidly-Incremented Tethered-Swimming Test for Defining Domain-Specific Training Zones

Journal of Human Kinetics ◽

10.1515/hukin-2017-0053 ◽

2017 ◽

Vol 57 (1) ◽

pp. 117-128

Author(s):

Dalton M. Pessôa Filho ◽

Leandro O.C. Siqueira ◽

Astor R. Simionato ◽

Mário A.C. Espada ◽

Daniel S. Pestana ◽

...

Keyword(s):

Gas Exchange ◽

Work Rate ◽

Metabolic Rates ◽

Incremental Test ◽

Domain Specific ◽

Respiratory Compensation ◽

Exercise Economy ◽

Constant Work Rate ◽

Swimming Test ◽

Gas Exchange Threshold

AbstractThe purpose of this study was to investigate whether a tethered-swimming incremental test comprising small increases in resistive force applied every 60 seconds could delineate the isocapnic region during rapidly-incremented exercise. Sixteen competitive swimmers (male, n = 11; female, n = 5) performed: (a) a test to determine highest force during 30 seconds of all-out tethered swimming (Favg) and the ΔF, which represented the difference between Favg and the force required to maintain body alignment (Fbase), and (b) an incremental test beginning with 60 seconds of tethered swimming against a load that exceeded Fbase by 30% of ΔF followed by increments of 5% of ΔF every 60 seconds. This incremental test was continued until the limit of tolerance with pulmonary gas exchange (rates of oxygen uptake and carbon dioxide production) and ventilatory (rate of minute ventilation) data collected breath by breath. These data were subsequently analyzed to determine whether two breakpoints defining the isocapnic region (i.e., gas exchange threshold and respiratory compensation point) were present. We also determined the peak rate of O2 uptake and exercise economy during the incremental test. The gas exchange threshold and respiratory compensation point were observed for each test such that the associated metabolic rates, which bound the heavy-intensity domain during constant-work-rate exercise, could be determined. Significant correlations (Spearman’s) were observed for exercise economy along with (a) peak rate of oxygen uptake (ρ = .562; p < 0.025), and (b) metabolic rate at gas exchange threshold (ρ = −.759; p < 0.005). A rapidly-incremented tethered-swimming test allows for determination of the metabolic rates that define zones for domain-specific constant-work-rate training.

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O2 Uptake in hyperthyroidism during constant work rate and incremental exercise

European Journal of Applied Physiology and Occupational Physiology ◽

10.1007/bf00571550 ◽

1991 ◽

Vol 62 (4) ◽

pp. 261-267 ◽

Cited By ~ 8

Author(s):

I. Ben-Dov ◽

K. E. Sietsema ◽

K. Wasserman

Keyword(s):

Work Rate ◽

Incremental Exercise ◽

O2 Uptake ◽

Constant Work Rate

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Muscle metabolic responses to exercise above and below the “critical power” assessed using 31P-MRS

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00731.2007 ◽

2008 ◽

Vol 294 (2) ◽

pp. R585-R593 ◽

Cited By ~ 246

Author(s):

Andrew M. Jones ◽

Daryl P. Wilkerson ◽

Fred DiMenna ◽

Jonathan Fulford ◽

David C. Poole

Keyword(s):

Critical Power ◽

Quadriceps Muscle ◽

High Energy ◽

Knee Extension ◽

Work Rate ◽

Metabolic Responses ◽

Time To Exhaustion ◽

Resonance Spectroscopy ◽

High Energy Phosphates ◽

Constant Work Rate

We tested the hypothesis that the asymptote of the hyperbolic relationship between work rate and time to exhaustion during muscular exercise, the “critical power” (CP), represents the highest constant work rate that can be sustained without a progressive loss of homeostasis [as assessed using 31P magnetic resonance spectroscopy (MRS) measurements of muscle metabolites]. Six healthy male subjects initially completed single-leg knee-extension exercise at three to four different constant work rates to the limit of tolerance (range 3–18 min) for estimation of the CP (mean ± SD, 20 ± 2 W). Subsequently, the subjects exercised at work rates 10% below CP (<CP) for 20 min and 10% above CP (>CP) for as long as possible, while the metabolic responses in the contracting quadriceps muscle, i.e., phosphorylcreatine concentration ([PCr]), Pi concentration ([Pi]), and pH, were estimated using 31P-MRS. All subjects completed 20 min of <CP exercise without duress, whereas the limit of tolerance during >CP exercise was 14.7 ± 7.1 min. During <CP exercise, stable values for [PCr], [Pi], and pH were attained within 3 min after the onset of exercise, and there were no further significant changes in these variables (end-exercise values = 68 ± 11% of baseline [PCr], 314 ± 216% of baseline [Pi], and pH 7.01 ± 0.03). During >CP exercise, however, [PCr] continued to fall to the point of exhaustion and [Pi] and pH changed precipitously to values that are typically observed at the termination of high-intensity exhaustive exercise (end-exercise values = 26 ± 16% of baseline [PCr], 564 ± 167% of baseline [Pi], and pH 6.87 ± 0.10, all P < 0.05 vs. <CP exercise). These data support the hypothesis that the CP represents the highest constant work rate that can be sustained without a progressive depletion of muscle high-energy phosphates and a rapid accumulation of metabolites (i.e., H+ concentration and [Pi]), which have been associated with the fatigue process.

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Establishing the V̇o2 versus constant-work-rate relationship from ramp-incremental exercise: simple strategies for an unsolved problem

Journal of Applied Physiology ◽

10.1152/japplphysiol.00508.2019 ◽

2019 ◽

Vol 127 (6) ◽

pp. 1519-1527 ◽

Cited By ~ 13

Author(s):

Danilo Iannetta ◽

Rafael de Almeida Azevedo ◽

Daniel A. Keir ◽

Juan M. Murias

Keyword(s):

Lactate Threshold ◽

Unsolved Problem ◽

Critical Power ◽

Work Rate ◽

Incremental Exercise ◽

Mean Response Time ◽

Constant Work Rate ◽

Ramp Exercise ◽

The Mean ◽

Highly Correlated

The dissociation between constant work rate of O2 uptake (V̇o2) and ramp V̇o2 at a given work rate might be mitigated during slowly increasing ramp protocols. This study characterized the V̇o2 dynamics in response to five different ramp protocols and constant-work-rate trials at the maximal metabolic steady state (MMSS) to characterize 1) the V̇o2 gain (G) in the moderate, heavy, and severe domains, 2) the mean response time of V̇o2 (MRT), and 3) the work rates at lactate threshold (LT) and respiratory compensation point (RCP). Eleven young individuals performed five ramp tests (5, 10, 15, 25, and 30 W/min), four to five time-to-exhaustions for critical power estimation, and two to three constant-work-rate trials for confirmation of the work rate at MMSS. G was greatest during the slowest ramp and progressively decreased with increasing ramp slopes (from ~12 to ~8 ml·min−1·W−1, P < 0.05). The MRT was smallest during the slowest ramp slopes and progressively increased with faster ramp slopes (1 ± 1, 2 ± 1, 5 ± 3, and 10 ± 4, 15 ± 6 W, P < 0.05). After “left shifting” the ramp V̇o2 by the MRT, the work rate at LT was constant regardless of the ramp slope (~150 W, P > 0.05). The work rate at MMSS was 215 ± 55 W and was similar and highly correlated with the work rate at RCP during the 5 W/min ramp ( P > 0.05, r = 0.99; Lin’s concordance coefficient = 0.99; bias = −3 W; root mean square error = 6 W). Findings showed that the dynamics of V̇o2 (i.e., G) during ramp exercise explain the apparent dichotomy existing with constant-work-rate exercise. When these dynamics are appropriately “resolved”, LT is constant regardless of the ramp slope of choice, and RCP and MMSS display minimal variations between each other. NEW & NOTEWORTHY This study demonstrates that the dynamics of V̇o2 during ramp-incremental exercise are dependent on the characteristics of the increments in work rate, such that during slow-incrementing ramp protocols the magnitude of the dissociation between ramp V̇o2 and constant V̇o2 at a given work rate is reduced. Accurately accounting for these dynamics ensures correct characterizations of the V̇o2 kinetics at ramp onset and allows appropriate comparisons between ramp and constant-work-rate exercise-derived indexes of exercise intensity.

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