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1.
Eur J Appl Physiol ; 119(4): 941-949, 2019 Apr.
Article in English | MEDLINE | ID: mdl-30694386

ABSTRACT

PURPOSE: The three-parameter model of critical power (3-p) implies that in the severe exercise intensity domain time to exhaustion (Tlim) decreases hyperbolically with power output starting from the power asymptote (critical power, wcr) and reaching 0 s at a finite power limit (w0) thanks to a negative time asymptote (k). We aimed to validate 3-p for short Tlim and to test the hypothesis that w0 represents the maximal instantaneous muscular power. METHODS: Ten subjects performed an incremental test and nine constant-power trials to exhaustion on an electronically braked cycle ergometer. All trials were fitted to 3-p by means of non-linear regression, and those with Tlim greater than 2 min also to the 2-parameter model (2-p), obtained constraining k to 0 s. Five vertical squat jumps on a force platform were also performed to determine the single-leg (i.e., halved) maximal instantaneous power. RESULTS: Tlim ranged from 26 ± 4 s to 15.7 ± 4.9 min. In 3-p, with respect to 2-p, wcr was identical (177 ± 26 W), while curvature constant W' was higher (17.0 ± 4.3 vs 15.9 ± 4.2 kJ, p < 0.01). 3-p-derived w0 was lower than single-leg maximal instantaneous power (1184 ± 265 vs 1554 ± 235 W, p < 0.01). CONCLUSIONS: 3-p is a good descriptor of the work capacity above wcr up to Tlim as short as 20 s. However, since there is a discrepancy between estimated w0 and measured maximal instantaneous power, a modification of the model has been proposed.


Subject(s)
Energy Metabolism/physiology , Exercise Test , Exercise/physiology , Physical Endurance/physiology , Adult , Humans , Male , Oxygen Consumption/physiology , Task Performance and Analysis , Young Adult
2.
Respir Physiol Neurobiol ; 255: 17-21, 2018 09.
Article in English | MEDLINE | ID: mdl-29733980

ABSTRACT

If, as postulated, the end of the steady state phase (φ2) of cardiovascular responses to apnoea corresponds to the physiological breaking point, then we may hypothesize that φ2 should become visible if exercise apnoeas are performed in pure oxygen. We tested this hypothesis on 9 professional divers by means of continuous recording of blood pressure (BP), heart rate (fH), stroke volume (QS), and arterial oxygen saturation (SpO2) during dry maximal exercising apnoeas in ambient air and in oxygen. Apnoeas lasted 45.0 ±â€¯16.9 s in air and 77.0 ±â€¯28.9 s in oxygen (p < 0.05). In air, no φ2 was observed. Conversely, in oxygen, a φ2 of 28 ±â€¯5 s duration appeared, during which systolic BP (185 ±â€¯29 mmHg), fH (93 ±â€¯16 bpm) and QS (91 ±â€¯16 ml) remained stable. End-apnoea SpO2 was 95.5 ±â€¯1.9% in air and 100% in oxygen. The results support the tested hypothesis.


Subject(s)
Air , Apnea/physiopathology , Cardiovascular System/physiopathology , Exercise/physiology , Oxygen , Adult , Blood Pressure/physiology , Diving , Heart Rate/physiology , Humans , Male , Oxygen/metabolism , Stroke Volume/physiology
3.
Eur J Appl Physiol ; 117(9): 1859-1867, 2017 Sep.
Article in English | MEDLINE | ID: mdl-28687955

ABSTRACT

INTRODUCTION: We tested the linear critical power ([Formula: see text]) model for discrete incremental ramp exercise implying recovery intervals at the end of each step. METHODS: Seven subjects performed incremental (power increment 25 W) stepwise ramps to subject's exhaustion, with recovery intervals at the end of each step. Ramps' slopes (S) were 0.83, 0.42, 0.28, 0.21, and 0.08 W s-1; recovery durations (t r) were 0 (continuous stepwise ramps), 60, and 180 s (discontinuous stepwise ramps). We determined the energy store component (W'), the peak power ([Formula: see text]), and [Formula: see text]. RESULTS: When t r = 0 s, [Formula: see text] and W' were 187 ± 26 W and 14.5 ± 5.8 kJ, respectively. When t r = 60 or 180 s, the model for ramp exercise provided inconsistent [Formula: see text] values. A more general model, implying a quadratic [Formula: see text] versus [Formula: see text] relationship, was developed. This model yielded, for t r = 60 s, [Formula: see text] = 189 ± 48 W and W' = 18.6 ± 17.8 kJ, and for t r = 180 s, [Formula: see text] = 190 ± 34 W, and W' = 16.4 ± 16.7 kJ. These [Formula: see text] and W' did not differ from the corresponding values for t r = 0 s. Nevertheless, the overall amount of energy sustaining work above [Formula: see text], due to energy store reconstitution during recovery intervals, was higher the longer t r, whence higher [Formula: see text] values. CONCLUSIONS: The linear [Formula: see text] model for ramp exercise represents a particular case (for t r = 0 s) of a more general model, accounting for energy resynthesis following oxygen deficit payment during recovery.


Subject(s)
Exercise Tolerance , High-Intensity Interval Training/methods , Oxygen Consumption , Adult , Female , Humans , Male , Muscle, Skeletal/physiology , Random Allocation , Recovery of Function
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