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Journal ArticleDOI

Power-Velocity and Power-Efficiency Implications in the Limitation of Ramp Incremental Cycle Ergometry: Reply to Morales-Alamo et al

15 Feb 2016-Journal of Applied Physiology (American Physiological Society)-Vol. 120, Iss: 4, pp 477-477

TL;DR: To the editor: The authors thank Morales-Alamo et al. for raising important questions worthy of further discussion and whether the limit of tolerance in ramp-incremental exercise is reached with a reserve in power producing capacity.
Abstract: to the editor: We thank Morales-Alamo et al. ([5][1]) for raising important questions worthy of further discussion. A key concern of both our studies ([3][2], [4][3]) is whether the limit of tolerance (LoT) in ramp-incremental exercise is reached with a reserve in power producing capacity. To this

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Power-Velocity and Power-Efficiency Implications in the Limitation of Ramp
Incremental Cycle Ergometry: Reply to Morales-Alamo et al.
Carrie Ferguson,
1
Daniel T. Cannon,
2
Lindsey A. Wylde,
1
Alan P. Benson,
1
and X Harry B. Rossiter
1,3
1
School of Biomedical Sciences & Multidisciplinary Cardiovascular Research Centre, Faculty of Biological Sciences,
University of Leeds, Leeds, United Kingdom;
2
School of Exercise & Nutritional Sciences, San Diego State University, San
Diego, California; and
3
Rehabilitation Clinical Trials Center, Division of Respiratory & Critical Care Physiology &
Medicine, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, California
TO THE EDITOR: We thank Morales-Alamo et al. (5) for raising
important questions worthy of further discussion. A key con-
cern of both our studies (3, 4) is whether the limit of tolerance
(LoT) in ramp-incremental exercise is reached with a reserve in
power producing capacity. To this end, we made three impor-
tant measurements in endurance-trained men (V
˙
O
2max
130
32% predicted) immediately at LoT: power of hyperbolic
cycling (55 rpm, 310 58 W); power required by the task
(352 58 W); and maximal isokinetic power, termed LoT
P
ISO
(80 rpm, 391 72 W). LoT P
ISO
was not different from
the power required by the task, hence no reserve in maximal
evocable power was evident. The fact that hyperbolic power at
LoT was lower than task power is not the relevant comparison,
and is likely related to dissipation of flywheel inertia. Impor-
tantly, peak power production at the crank was not different at
LoT between 55 and 80 rpm (Fig. 2, B–C, in Ref. 3).
Increasing cadence during the isokinetic switch to a velocity
similar to the ramp incremental, achieved a small increase in
mean power, but this was insufficient to exceed the task
requirement (P 0.116, effect size 0.81, ␤⫽0.73).
Interestingly, this finding is similar to Morales-Alamo et al.
(4), where mean isokinetic power 10 s after intolerance (318
55 W) was only 10% greater than maximal incremental fly-
wheel power (290 36 W).
We commend Morales-Alamo et al. (4) in their rapid occlu-
sion and biopsy to preserve and measure muscle metabolic
conditions at 10 and 60 s after LoT and show an intramuscular
metabolic reserve. We were unable to reference this insightful
work, because our manuscript was submitted before their study
was published. Similarly, we found an intramuscular metabolic
reserve at LoT, albeit during bilateral knee extension, where
5% of quadriceps volume reached extreme metabolic condi-
tions (2). Thus it is perhaps unsurprising that a small biopsy
sample also found a reserve. Although we agree that intramus-
cular fatigue alone cannot explain task failure, a metabolic
reserve is not evidence that the muscle is capable of being fully
activated or increasing power generation at intolerance. To
clarify, our volunteers were well-motivated and strongly en-
couraged throughout both ramp-incremental and isokinetic
phases of the test and showed high test-retest reproducibility
(3). Despite this, we found a 40% reduction in maximal
evocable muscle activity and 10% lower activity-normalized
isokinetic power, suggesting muscle metabolism and activation
conspire to limit power to equal the task at LoT.
Morales-Alamo et al. raise an interesting question with their
comment: “higher shortening speed requires more ATP.” In
isolated mouse fast-twitch fiber bundles, efficiency increases
with velocity, peaking at about one-third peak velocity (1).
Unfortunately, the entire velocity-efficiency curve is not char-
acterized for cycling, but it seems reasonable that the small
increase in power we observed between 55 and 80 rpm (3)
may not necessitate a greater ATP turnover should efficiency
increase.
Although we do not agree that at intolerance during whole
body incremental exercise power can be greatly increased
above the task requirement— both our studies (3, 4) provide
evidence to the contrary—clearly there remains considerable
work to uncover the integrated mechanisms limiting whole
body exercise under incremental, constant, or self-paced con-
ditions.
DISCLOSURES
No conflicts of interest, financial or otherwise, are declared by the author(s).
AUTHOR CONTRIBUTIONS
Author contributions: C.F. and H.B.R. drafted manuscript; C.F., D.T.C.,
L.A.W., A.P.B., and H.B.R. edited and revised manuscript; C.F., D.T.C.,
L.A.W., A.P.B., and H.B.R. approved final version of manuscript.
REFERENCES
1. Barclay CJ. Mechanical efficiency and fatigue of fast and slow muscles of
the mouse. J Physiol 497: 781–794, 1996.
2. Cannon DT, Howe FA, Whipp BJ, Ward SA, McIntyre DJ, Ladroue C,
Griffiths JR, Kemp GJ, Rossiter HB. Muscle metabolism and activation
heterogeneity by combined 31P chemical shift and T2 imaging, and pul-
monary O
2
uptake during incremental knee-extensor exercise. J Appl
Physiol 115: 839 –849, 2013.
3. Ferguson C, Wylde LA, Benson AP, Cannon DT, Rossiter HB. No
reserve in isokinetic cycling power at intolerance during ramp incremental
exercise in endurance-trained men. J Appl Physiol 120: 70 –77, 2016.
4. Morales-Alamo D, Losa-Reyna J, Torres-Peralta R, Martin-Rincon M,
Perez-Valera M, Curtelin D, Ponce-Gonzalez JG, Santana A, Calbet
JA. What limits performance during whole-body incremental exercise to
exhaustion in humans? J Physiol 593: 4631–4648, 2015.
5. Morales-Alamo D, Martin-Rincon M, Perez-Valera M, Marcora S,
Calbet JAL. No functional reserve at exhaustion in endurance-trained
men? J Appl Physiol; doi:10.1152/japplphysiol.01006.2015.
Address for reprint requests and other correspondence: C. Ferguson, School
of Biomedical Sciences & Multidisciplinary Cardiovascular Research Centre,
Faculty of Biological Sciences, Univ. of Leeds, Leeds LS2 9JT, UK (e-mail:
c.ferguson@leeds.ac.uk).
J Appl Physiol 120: 477, 2016;
doi:10.1152/japplphysiol.01067.2015.
Letter to the Editor
8750-7587/16 Copyright
©
2016 the American Physiological Societyhttp://www.jappl.org 477
Downloaded from www.physiology.org/journal/jappl at Univ De Las Palmas De Gran Canaria (193.145.130.058) on May 23, 2019.
Citations
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Journal ArticleDOI
TL;DR: COPD patients are more fatigable than controls, but this fatigue is insufficient to constrain locomotor power and define exercise intolerance, and is apportioned into the reduction in muscle activation and muscle fatigue.
Abstract: Chronic obstructive pulmonary disease (COPD) patients exhibit skeletal muscle abnormalities that contribute to high fatigability. Whether muscle fatigue is sufficient to limit whole body exercise i...

15 citations


Journal ArticleDOI
TL;DR: Those without a "power reserve" exhibit greater peripheral muscle fatigue and reduced muscle endurance, supporting the hypothesis that exhaustion occurs at a specific level of neuromuscular fatigue.
Abstract: This study demonstrates that the mechanisms associated with the limit of tolerance during ramp-incremental cycling exercise differ between those who are capable of generating power output in excess...

6 citations


Cites background or methods or result from "Power-Velocity and Power-Efficiency..."

  • ...There were no between group differences in PisoPRE and POpeak (Table 1), but due to a higher (p 0.05) PisoPOST in RES (448 ± 87 W) compared to NRES (364 ± 77 W), ΔPReserve was greater (p<0.05) in RES (24.4 ± 10.0...

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  • ...A dichotomy in ΔPReserve within the subject sample was observed in which there was a grouping of subjects with very little difference between the end-RI POpeak and the PisoPOST at 70 rpm (< 5% power reserve) and a group with a much larger difference between the two peak torque values (>15% power reserve), with no subjects found in the 5% to 15% region (see Fig....

    [...]

  • ...Power reserve was calculated as the percent difference between POpeak and PisoPOST (Ferguson et al., 2016): Equation 1: ([ PisoPOST - POpeak ] / POpeak) · 100...

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  • ...This lack of a “power reserve” at the LoT has been reported in publications by Burnley, 2010; Macintosh et al., 2012; Coelho et al., 2015; and Ferguson et al., 2016....

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  • ...Isokinetic knee-extension power at 55 rpm (which was set as the lower cut-off limit for stopping the RI test) was reduced 179 5 W (PisoPRE, 675 150 W; PisoPOST, 497 155 W)....

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Journal ArticleDOI
TL;DR: Isokinetic power measured immediately following intolerance consistently overestimated critical power, and an adjunct of 30 s maximal isokinetic cycling immediately following the limit of tolerance does not approximate critical power.
Abstract: The asymptote of the hyperbolic power-duration relationship, critical power (CP), demarcates sustainable from non-sustainable exercise. CP is a salient parameter within the theoretical framework determining exercise tolerance. However, measuring CP is time consuming – typically 4 constant-power exercise tests to intolerance, or a 3-min all-out sprint is required. To determine whether 30 s of maximal isokinetic cycling, immediately following the limit of tolerance, approximates CP. Fifteen participants (7 women, 8 men, 23±5 yr, 71±12 kg, VO2peak 4.39±1.04 L·min−1; 61±9 mL·kg·min−1) completed 4 constant supra-CP exercise tests to intolerance. Each test was followed immediately by a 30 s maximal isokinetic effort at 80 rpm. Mean isokinetic power was compared to the known CP. Mean±SD CP was 159±47 W (CI95 133, 185 W). Maximal isokinetic power immediately following intolerance was greater (p 0.07). However, this closest estimation, following the longest duration constant-power test, resulted in 21 W of mean bias and wide limits of agreement (±84 W). Isokinetic power measured immediately following intolerance consistently overestimated critical power. Thus, an adjunct of 30 s maximal isokinetic cycling immediately following the limit of tolerance does not approximate critical power.

2 citations


Journal ArticleDOI
Austin R. Swisher1, Blake Koehn1, Stanley Yong1, Jonathan Cunha1  +2 moreInstitutions (2)
TL;DR: Instantaneous isokinetic power production at the limit of tolerance exceeded that of the task requirement, regardless of the constant, or ramp work rate profile.
Abstract: PURPOSEWe aimed to measure 1) the dynamics of locomotor fatigue during constant supra-critical power cycling, and 2) the magnitude of any reserve in locomotor power at intolerance to constant and ramp-incremental cycling in recreationally-active volunteers.METHODSFifteen participants (7 wome

1 citations


Journal ArticleDOI
TL;DR: In RI-50 and RI-25, the absence of a power reserve suggests neuromuscular fatigue was insufficient to limit the exercise, and additional mechanisms contributed to intolerance at V˙O2max.
Abstract: INTRODUCTION The mechanism(s) of exercise intolerance at V˙O2max remain poorly understood. In health, standard ramp-incremental (RI) exercise is limited by fatigue-induced reductions in maximum voluntary cycling power. Whether neuromuscular fatigue also limits exercise when the RI rate is slow and RI peak power at intolerance is lower than standard RI exercise, is unknown. METHODS In twelve healthy participants, maximal voluntary cycling power was measured during a short (~6 s) isokinetic effort at 80 rpm (Piso) at baseline and, using an instantaneous switch from cadence-independent to isokinetic cycling, immediately at the limit of RI exercise with RI rates of 50, 25, and 10 W·min-1 (RI-50, RI-25, and RI-10). Breath-by-breath pulmonary gas exchange was measured throughout. RESULTS Baseline Piso was not different among RI rates (analysis of variance; P > 0.05). Tolerable duration increased with decreasing RI rate (RI-50, 411 ± 58 s vs RI-25, 732 ± 93 s vs RI-10, 1531 ± 288 s; P 0.05), but RI peak power decreased with RI rate (RI-50, 361 ± 48 W vs RI-25, 323 ± 39 W vs RI-10, 275 ± 38 W; P 0.05), thus there was no "power reserve." In RI-10, Piso was greater than RI peak power at intolerance (P < 0.001), that is, there was a "power reserve." CONCLUSIONS In RI-50 and RI-25, the absence of a power reserve suggests the neuromuscular fatigue-induced reduction in Piso coincided with V˙O2max and limited the exercise. In RI-10, the power reserve suggests neuromuscular fatigue was insufficient to limit the exercise, and additional mechanisms contributed to intolerance at V˙O2max.

1 citations


Cites background from "Power-Velocity and Power-Efficiency..."

  • ...This is despite submaximalmotor-unit recruitment at the limit of RI exercise, meaning that some muscle fibers maintain a metabolic reserve that would be capable of supporting increased ATP turnover (and power generation), were participants capable of activating these fibers at intolerance (13,41,42)....

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References
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Journal ArticleDOI
Christopher John Barclay1Institutions (1)
TL;DR: It was concluded that the decrease in initial mechanical efficiency reflected a decrease in the efficiency of energy conversion by the crossbridges.
Abstract: 1. In this study, the efficiency of energy conversion in skeletal muscles from the mouse was determined before and after a series of contractions that produced a moderate level of fatigue. 2. Initial mechanical efficiency was defined as the ratio of mechanical power output to the rate of initial enthalpy output. The rate of initial enthalpy output was the sum of the power output and rate of initial heat output. Heat output was measured using a thermopile with high temporal resolution. 3. Experiments were performed in vitro (25 degrees C) using bundles of fibres from fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscles from mice. Muscles were fatigued using a series of thirty isometric tetani. Initial mechanical efficiency was determined before and again immediately after the fatigue protocol using a series of isovelocity contractions at shortening velocities between 0 and the maximum shortening velocity (Vmax). Efficiency was determined over the second half of the shortening at each velocity. 4. The fatigue protocol significantly reduced maximum isometric force Vmax, maximum power output and flattened the force-velocity curve. The magnitude of these effects was greater in EDL muscle than soleus muscle. In unfatigued muscle, the maximum mechanical efficiency was 0.333 for EDL muscles and 0.425 for soleus muscles. In both muscle types, the fatiguing contractions caused maximum efficiency to decrease. The magnitude of the decrease was 15% of the pre-fatigue value in EDL and 9% in soleus. 5. In a separate series of experiments, the effect of the fatigue protocol on the partitioning of energy expenditure between crossbridge and non-crossbridge sources was determined. Data from these experiments enabled the efficiency of energy conversion by the crossbridges to be estimated. It was concluded that the decrease in initial mechanical efficiency reflected a decrease in the efficiency of energy conversion by the crossbridges.

151 citations


"Power-Velocity and Power-Efficiency..." refers background in this paper

  • ...” In isolated mouse fast-twitch fiber bundles, efficiency increases with velocity, peaking at about one-third peak velocity (1)....

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Abstract: To determine the mechanisms causing task failure during incremental exercise to exhaustion (IE), sprint performance (10 s all-out isokinetic) and muscle metabolites were measured before (control) and immediately after IE in normoxia (P(IO2) 143 mmHg) and hypoxia (P(IO2): 73 mmHg) in 22 men (22 ± 3 years). After IE, subjects recovered for either 10 or 60 s, with open circulation or bilateral leg occlusion (300 mmHg) in random order. This was followed by a 10 s sprint with open circulation. Post-IE peak power output (W(peak)) was higher than the power output reached at exhaustion during IE (P < 0.05). After 10 and 60 s recovery in normoxia, W(peak) was reduced by 38 ± 9 and 22 ± 10% without occlusion, and 61 ± 8 and 47 ± 10% with occlusion (P < 0.05). Following 10 s occlusion, W(peak) was 20% higher in hypoxia than normoxia (P < 0.05), despite similar muscle lactate accumulation ([La]) and phosphocreatine and ATP reduction. Sprint performance and anaerobic ATP resynthesis were greater after 60 s compared with 10 s occlusions, despite the higher [La] and [H(+)] after 60 s compared with 10 s occlusion recovery (P < 0.05). The mean rate of ATP turnover during the 60 s occlusion was 0.180 ± 0.133 mmol (kg wet wt)(-1) s(-1), i.e. equivalent to 32% of leg peak O2 uptake (the energy expended by the ion pumps). A greater degree of recovery is achieved, however, without occlusion. In conclusion, during incremental exercise task failure is not due to metabolite accumulation or lack of energy resources. Anaerobic metabolism, despite the accumulation of lactate and H(+), facilitates early recovery even in anoxia. This points to central mechanisms as the principal determinants of task failure both in normoxia and hypoxia, with lower peripheral contribution in hypoxia.

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TL;DR: The limit of tolerance was attained with wide heterogeneity in substrate depletion and fatigue-related metabolite accumulation, with extreme metabolic perturbation isolated to only a small volume of active muscle (<5%).
Abstract: The integration of skeletal muscle substrate depletion, metabolite accumulation, and fatigue during large muscle-mass exercise is not well understood. Measurement of intramuscular energy store degr...

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"Power-Velocity and Power-Efficiency..." refers background in this paper

  • ...Similarly, we found an intramuscular metabolic reserve at LoT, albeit during bilateral knee extension, where 5% of quadriceps volume reached extreme metabolic conditions (2)....

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Journal ArticleDOI
TL;DR: The absence of a power reserve suggests both the perceptual and physiological limits of maximum voluntary power production are not widely dissociated at LoT in this population of endurance-trained men.
Abstract: During whole body exercise in health, maximal oxygen uptake (Vo2max) is typically attained at or immediately before the limit of tolerance (LoT). At the Vo2max and LoT of incremental exercise, a fundamental, but unresolved, question is whether maximal evocable power can be increased above the task requirement, i.e., whether there is a "power reserve" at the LoT. Using an instantaneous switch from cadence-independent (hyperbolic) to isokinetic cycle ergometry, we determined maximal evocable power at the limit of ramp-incremental exercise. We hypothesized that in endurance-trained men at LoT, maximal (4 s) isokinetic power would not differ from the power required by the task. Baseline isokinetic power at 80 rpm (Piso; measured at the pedals) and summed integrated EMG from five leg muscles (ΣiEMG) were measured in 12 endurance-trained men (Vo2max = 4.2 ± 1.0 l/min). Participants then completed a ramp incremental exercise test (20-25 W/min), with instantaneous measurement of Piso and ΣiEMG at the LoT. Piso decreased from 788 ± 103 W at baseline to 391 ± 72 W at LoT, which was not different from the required ramp-incremental flywheel power (352 ± 58 W; P > 0.05). At LoT, the relative reduction in Piso was greater than the relative reduction in the isokinetic ΣiEMG (50 ± 9 vs. 63 ± 10% of baseline; P < 0.05). During maximal ramp incremental exercise in endurance-trained men, maximum voluntary power is not different from the power required by the task and is consequent to both central and peripheral limitations in evocable power. The absence of a power reserve suggests both the perceptual and physiological limits of maximum voluntary power production are not widely dissociated at LoT in this population.

17 citations


"Power-Velocity and Power-Efficiency..." refers background or result in this paper

  • ...A key concern of both our studies (3, 4) is whether the limit of tolerance (LoT) in ramp-incremental exercise is reached with a reserve in power producing capacity....

    [...]

  • ...Although we do not agree that at intolerance during whole body incremental exercise power can be greatly increased above the task requirement—both our studies (3, 4) provide evidence to the contrary—clearly there remains considerable work to uncover the integrated mechanisms limiting whole body exercise under incremental, constant, or self-paced conditions....

    [...]

  • ...Unfortunately, the entire velocity-efficiency curve is not characterized for cycling, but it seems reasonable that the small increase in power we observed between 55 and 80 rpm (3) may not necessitate a greater ATP turnover should efficiency increase....

    [...]

  • ...To clarify, our volunteers were well-motivated and strongly encouraged throughout both ramp-incremental and isokinetic phases of the test and showed high test-retest reproducibility (3)....

    [...]


Journal ArticleDOI
TL;DR: Saltin’s studies clearly demonstrated that training in deconditioned subjects increases Vo2 max by, and the authors remark that the main factor limiting Vo2max in sedentary people is O2 extraction capacity.
Abstract: to the editor: We read with great interest the study by Ferguson et al. ([2][1]). The authors remark that the main factor limiting Vo2 max in sedentary people is O2 extraction capacity. However, Saltin’s studies clearly demonstrated that training in deconditioned subjects increases Vo2 max by

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"Power-Velocity and Power-Efficiency..." refers background in this paper

  • ...(5) for raising important questions worthy of further discussion....

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