Attenuation of Muscle Deoxygenation Precedes EMG Threshold in Normoxia and Hypoxia

Osawa, Takuya; Kime, Ryotaro; Hamaoka, Toshiyuki; Katsumura, Toshihito; Yamamoto, Masayoshi

doi:10.1249/mss.0b013e3182100261

Cited by 42 publications

(52 citation statements)

References 43 publications

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“…detected between control and occlusion RMS at 80% P peak and MedPF at 110% P peak . These findings differ from those of prior studies, demonstrating similar EMG characteristics between normoxia and hypoxia (15,41). The present results may differ from previous findings due to greater magnitude of O 2 delivery reduction with occlusion compared with hypoxia.…”

Section: Discussioncontrasting

confidence: 99%

“…In the present study, fractional O 2 extraction was significantly greater for occlusion than for control. This is consistent with previous reports of alterations in the fractional O 2 extraction with varying inspired O 2 concentrations (41,46,51 (16,24,29,33). The similar peak plateaus in microvascular hematocrit (i.e., total-[HbϩMb]) in the present study for control exercise suggest that the peak microvascular hematocrit, and, therefore, Ḋ o 2 , is constrained for a given condition.…”

Section: Discussionsupporting

confidence: 93%

“…Consistent with these muscle physiological responses being independent of O 2 delivery, similar skeletal muscle electromyography (EMG) characteristics are expressed between normoxic and hypoxic exercise (15,41). In contrast, fractional O 2 extraction {indicated by deoxygenated hemoglobin ϩ myoglobin concentration, (deoxy[HbϩMb]) (10,14,19,20,22)} at T lim appears to be scaled to O 2 delivery, such that it is greater with hypoxia (41) and less with hyperoxia (51) than normoxia, respectively.…”

mentioning

confidence: 76%

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Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship

Broxterman

Ade

Craig

et al. 2015

Journal of Applied Physiology

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Broxterman RM, Ade CJ, Craig JC, Wilcox SL, Schlup SJ, Barstow TJ. Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship. J Appl Physiol 118: 880 -889, 2015. First published February 6, 2015 doi:10.1152/japplphysiol.00875.2014.-It was previously (Monod H, Scherrer J. Ergonomics 8: 329 -338, 1965 postulated that blood flow occlusion during exercise would reduce critical power (CP) to 0 Watts (W), while not altering the curvature constant (W=). We empirically assessed the influence of blood flow occlusion on CP, W=, and muscle oxygenation characteristics. Ten healthy men (age: 24.8 Ϯ 2.6 yr; height: 180 Ϯ 5 cm; weight: 84.6 Ϯ 10.1 kg) completed four constant-power handgrip exercise tests during both control blood flow (control) and blood flow occlusion (occlusion) for the determination of the power-duration relationship. Occlusion CP (Ϫ0.7 Ϯ 0.4 W) was significantly (P Ͻ 0.001) lower than control CP (4.1 Ϯ 0.7 W) and significantly (P Ͻ 0.001) lower than 0 W. Occlusion W= (808 Ϯ 155 J) was significantly (P Ͻ 0.001) different from control W= (558 Ϯ 129 J), and all 10 subjects demonstrated an increased occlusion W= with a mean increase of ϳ49%. The present findings support the aerobic nature of CP. The findings also demonstrate that the amount of work that can be performed above CP is constant for a given condition, but can vary across conditions. Moreover, this amount of work that can be performed above CP does not appear to be the determinant of W=, but rather a consequence of the depletion of intramuscular energy stores and/or the accumulation of fatigue-inducing metabolites, which limit exercise tolerance and determine W=. critical power; curvature constant; oxygen delivery; muscle ischemia THE ROBUST NATURE OF THE power-duration relationship (and its equivalents for other modes of exercise) has been well established (26, 27, 52). Nevertheless, the precise physiological mechanisms of the curvature constant (W=), and to a lesser degree critical power (CP), have remained elusive. The growing body of evidence supports that CP represents the highest attainable steady state for aerobic energy production without continually drawing on W= and, as such, demarcates the boundary between the heavy-and severe-intensity exercise domains (4,12,38,39,42,51). It is also evident that W= is a constant term that determines the limit of exercise tolerance (T lim ) for severe-intensity exercise (21, 55). Intramuscular energy stores (35,36,38), the accumulation of fatigue-inducing metabolites (7,18,21,28), and/or the magnitude of the severe-intensity domain (5, 51) have all been postulated to determine W=. Building evidence supports that complete utilization of W= is associated with consistent muscle phosphocreatine ([PCr]), inorganic phosphate ([P i ]), and hydrogen ion concentration ([H ϩ ]) perturbations, which may limit the amount of work performed above CP (28,43,51). Additionally, the rate of W= utilization (but not the magnitude of W=) is influenced by mani...

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Section: Discussioncontrasting

confidence: 99%

Section: Discussionsupporting

confidence: 93%

mentioning

confidence: 76%

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Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship

Broxterman

Ade

Craig

et al. 2015

Journal of Applied Physiology

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“…The HHb levels during CWE exceeded those observed (Neary et al 2001;DeLorey et al 2003;Grassi et al 2003) because of its higher WR during CWE. In the present study, differences in HHb values during the end phase, from 90% to 100% of V 4 O 2max , may be because of the "HHb slow component" during CWE (Jones et al 2006;Bailey et al 2009;), a progressive increase in HHb throughout the steady state portion of the exercise, and "the plateau point" during IRE (Legrand et al 2007;Boone et al 2009;Osawa et al 2011;Spencer et al 2012). In the present study, the typical HHb kinetics (Fig.…”

Section: Discussionsupporting

confidence: 51%

Muscle Oxygen Extraction Is Higher during Constant Work Exercise than during Incremental Ramp Exercise

Yamamoto

Tabira

2014

Tohoku J. Exp. Med.

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A cardiopulmonary exercise test (CPX) can provide objective measures of exercise capacity. Specifically, incremental ramp exercise (IRE) and constant work-rate exercise (CWE) protocols are frequently used in clinical practice and for research. The CWE endurance time has shown larger increases than other indexes assessed by IRE after rehabilitation intervention. Muscle oxygen extraction is one of the important physiological factors of exercise capacity; however, the differences in muscle oxygen kinetics between IRE and CWE remain unclear. The purpose of this study was to compare the muscle oxygen kinetics during IRE and CWE. Each of the 15 participants performed IRE and CWE to exhaustion on a cycle ergometer. Ventilatory and muscle deoxygenation responses were measured during the tests; muscle deoxygenation was determined using near-infrared spectroscopy. No differences in oxygen uptake and heart rate were observed between the two tests. A comparison of the muscle deoxygenation kinetics between the two tests indicated significantly greater deoxygenation during the CWE than during the IRE at all time points (p < 0.05). The muscle deoxygenation kinetics, as percentages of maximal oxygen uptake (V 4 O 2max ), were higher during CWE than during IRE, except at 80% of V 4 O 2max (p < 0.05). These results suggest that skeletal muscle during CWE extracts oxygen at a rate comparable to that during IRE, and that exercise capacity assessed using CWE might be linked to a higher overall O 2 extraction. The fact that endurance time during CWE is more sensitive to rehabilitation intervention may be due to improvements in muscle oxygen extraction.

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“…uscle activation, as represented by the amplitude of surface electromyogram (EMG) increases during incremental exercise to exhaustion (Taylor and Bronks, 1996;Osawa et al, 2011). Greater EMG amplitude may originate from the combination of progressive recruitment of additional motor units and increases in the firing rate to raise muscle contraction intensity with the progression of power output, as shown using different contraction modes (Gottlieb and Agarwal 1971;Ericson 1986;Weir et al, 1992;Gonzalez-Izal et al, 2012).…”

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confidence: 99%

Muscle Activation During Exercise in Severe Acute Hypoxia: Role of Absolute and Relative Intensity

Torres‐Peralta

Losa‐Reyna²,

González-Izal³

et al. 2014

High Altitude Medicine & Biology

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Torres-Peralta, Rafael, José Losa-Reyna, Miriam González-Izal, Ismael Perez-Suarez, Jaime Calle-Herrero, Mikel Izquierdo, and José A.L. Calbet. Muscle activation during exercise in severe acute hypoxia: Role of absolute and relative intensity. High Alt Med Biol 15:472-482, 2014.-The aim of this study was to determine the influence of severe acute hypoxia on muscle activation during whole body dynamic exercise. Eleven young men performed four incremental cycle ergometer tests to exhaustion breathing normoxic (F I o 2 = 0.21, two tests) or hypoxic gas (F I o 2 = 0.108, two tests). Surface electromyography (EMG) activities of rectus femoris (RF), vastus medialis (VL), vastus lateralis (VL), and biceps femoris (BF) were recorded. The two normoxic and the two hypoxic tests were averaged to reduce EMG variability. Peak Vo 2 was 34% lower in hypoxia than in normoxia ( p < 0.05). The EMG root mean square (RMS) increased with exercise intensity in all muscles ( p < 0.05), with greater effect in hypoxia than in normoxia in the RF and VM ( p < 0.05), and a similar trend in VL ( p = 0.10). At the same relative intensity, the RMS was greater in normoxia than in hypoxia in RF, VL, and BF ( p < 0.05), with a similar trend in VM ( p = 0.08). Median frequency increased with exercise intensity ( p < 0.05), and was higher in hypoxia than in normoxia in VL ( p < 0.05). Muscle contraction burst duration increased with exercise intensity in VM and VL ( p < 0.05), without clear effects of F I o 2 . No significant F I o 2 effects on frequency domain indices were observed when compared at the same relative intensity. In conclusion, muscle activation during whole body exercise increases almost linearly with exercise intensity, following a muscle-specific pattern, which is adjusted depending on the F I o 2 and the relative intensity of exercise. Both VL and VM are increasingly involved in power output generation with the increase of intensity and the reduction in F I o 2 .

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Attenuation of Muscle Deoxygenation Precedes EMG Threshold in Normoxia and Hypoxia

Abstract: These results suggest that the attenuation of muscle deoxygenation near VO2peak is related to and precedes changes in neuromuscular activity under normoxic and hypoxic conditions.

Cited by 42 publications

References 43 publications

Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship

Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship

Muscle Oxygen Extraction Is Higher during Constant Work Exercise than during Incremental Ramp Exercise

Muscle Activation During Exercise in Severe Acute Hypoxia: Role of Absolute and Relative Intensity

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