It is not possible to attain a metabolic steady state during exercise above the so‐called critical force or critical power. We tested the hypothesis that the muscle metabolic perturbations at the end ...of a bout of maximal isometric contractions, which yield a stable end‐test force (equal to the critical force), would be similar to that at task failure following submaximal contractions performed above the critical force. Eight healthy subjects (four female) performed isometric single knee‐extension exercise in the bore of a 1.5 T superconducting magnet on two occasions. Following familiarization, subjects performed the following exercises: (1) 60 maximal contractions (3 s contraction, 2 s rest); and (2) submaximal contractions (the same contraction regime performed at 54 ± 8% maximal voluntary contraction) to task failure. Phosphocreatine (PCr), inorganic phosphate (Pi) and diprotonated phosphate (H2PO4−) concentrations and pH were determined using 31P magnetic resonance spectroscopy throughout both tests. During the maximal contractions, force production fell from 213 ± 33 N to reach a plateau in the last 30 s of the test at 100 ± 20 N. The muscle metabolic responses at the end of each test were substantial, but not different between conditions: PCr was reduced (to 21 ± 12 and 17 ± 7% of baseline for maximal and submaximal contractions, respectively; P= 0.17), Pi was elevated (to 364 ± 98 and 363 ± 135% of baseline, respectively; P= 0.98) and pH reduced (to 6.64 ± 0.16 and 6.69 ± 0.17, respectively; P= 0.43). The H2PO4− was also elevated at the end of both tests (to 607 ± 252 and 556 ± 269% of baseline, respectively; P= 0.22). These data suggest that the exercise‐induced metabolic perturbations contributing to force depression in all‐out exercise are the same as those contributing to task failure during submaximal contractions.
To investigate the influence of β-alanine (BA) supplementation on muscle carnosine content, muscle pH and the power-duration relationship (i.e., critical power and W').
In a double-blind, randomized, ...placebo-controlled study, 20 recreationally-active males (22 ± 3 y, V°O
3.73 ± 0.44 L·min
) ingested either BA (6.4 g/d for 28 d) or placebo (PL) (6.4 g/d) for 28 d. Subjects completed an incremental test and two 3-min all-out tests separated by 1-min on a cycle ergometer pre- and post-supplementation. Muscle pH was assessed using
P-magnetic resonance spectroscopy (MRS) during incremental (INC KEE) and intermittent knee-extension exercise (INT KEE). Muscle carnosine content was determined using
H-MRS.
There were no differences in the change in muscle carnosine content from pre- to post-intervention (PL: 1 ± 16% vs. BA: -4 ± 25%) or in muscle pH during INC KEE or INT KEE (
> 0.05) between PL and BA, but blood pH (PL: -0.06 ± 0.10 vs. BA: 0.09 ± 0.13) during the incremental test was elevated post-supplementation in the BA group only (
< 0.05). The changes from pre- to post-supplementation in critical power (PL: -8 ± 18 W vs. BA: -6 ± 17 W) and W' (PL: 1.8 ± 3.3 kJ vs. BA: 1.5 ± 1.7 kJ) were not different between groups. No relationships were detected between muscle carnosine content and indices of exercise performance.
BA supplementation had no significant effect on muscle carnosine content and no influence on intramuscular pH during incremental or high-intensity intermittent knee-extension exercise. The small increase in blood pH following BA supplementation was not sufficient to significantly alter the power-duration relationship or exercise performance.
The curvilinear relationship between power output and the time for which it can be sustained is a fundamental and well-known feature of high-intensity exercise performance. This relationship ‘levels ...off’ at a ‘critical power’ (CP) that separates power outputs that can be sustained with stable values of, for example, muscle phosphocreatine, blood lactate, and pulmonary oxygen uptake (
V
˙
O
2
), from power outputs where these variables change continuously with time until their respective minimum and maximum values are reached and exercise intolerance occurs. The amount of work that can be done during exercise above CP (the so-called
W
′) is constant but may be utilized at different rates depending on the proximity of the exercise power output to CP. Traditionally, this two-parameter CP model has been employed to provide insights into physiological responses, fatigue mechanisms, and performance capacity during continuous constant power output exercise in discrete exercise intensity domains. However, many team sports (e.g., basketball, football, hockey, rugby) involve frequent changes in exercise intensity and, even in endurance sports (e.g., cycling, running), intensity may vary considerably with environmental/course conditions and pacing strategy. In recent years, the appeal of the CP concept has been broadened through its application to intermittent high-intensity exercise. With the assumptions that
W
′ is utilized during work intervals above CP and reconstituted during recovery intervals below CP, it can be shown that performance during intermittent exercise is related to four factors: the intensity and duration of the work intervals and the intensity and duration of the recovery intervals. However, while the utilization of
W
′ may be assumed to be linear, studies indicate that the reconstitution of
W
′ may be curvilinear with kinetics that are highly variable between individuals. This has led to the development of a new CP model for intermittent exercise in which the balance of
W
′ remaining (
W
BAL
′
) may be calculated with greater accuracy. Field trials of athletes performing stochastic exercise indicate that this
W
BAL
′
model can accurately predict the time at which
W
′ tends to zero and exhaustion is imminent. The
W
BAL
′
model potentially has important applications in the real-time monitoring of athlete fatigue progression in endurance and team sports, which may inform tactics and influence pacing strategy.
The first issue of EJSS in 2001 featured stellar contributions from great sport scientists who have gone on to serve the College in many roles—Romain Meeusen, Erich Müller, Maria Francesca ...Piacentini, Bengt Saltin, Jørn Wulff Helge, Taija Finni and Paavo Komi to mention a few—with articles covering the breadth of sport science from biomechanics, motor control and muscle physiology to physical activity, health and the cultural science of human movement. ...Wiley's partnership with Research4Life provides APC fee waivers and discounts for authors from low- and middle-income countries (Wiley, , b). Adventure awaits! CONFLICT OF INTEREST STATEMENT The authors declare no conflicts of interest.
We reinforce the key messages in our earlier review paper that critical power, rather than maximal lactate steady state, provides the better index for defining steady‐state vs non‐steady state ...physiological behaviour during exercise.
The purpose of this study was to assess whether end-test power output (EP, synonymous with âcritical powerâ) and the work
done above EP (WEP) during a 3 min all-out cycling test against a fixed ...resistance were affected by the manipulation of cadence
or pacing. Nine subjects performed a ramp test followed, in random order, by three cadence trials (in which flywheel resistance
was manipulated to achieve end-test cadences which varied by â¼20 r.p.m.) and two pacing trials (30 s at 100 or 130% of maximal
ramp test power, followed by 2.5 min all-out effort against standard resistance). End-test power output was calculated as
the mean power output over the final 30 s and the WEP as the powerâtime integral over 180 s for each trial. End-test power
output was unaffected by reducing cadence below that of the âstandard testâ but was reduced by â¼10 W on the adoption of a
higher cadence 244 ± 41 W for high cadence (at an end-test cadence of 95 ± 7 r.p.m.), 254 ± 40 W for the standard test (at
88 ± 6 r.p.m.) and 251 ± 38 W for low cadence (at 77 ± 5 r.p.m.). Pacing over the initial 30 s of the test had no effect
on the EP or WEP estimates in comparison with the standard trial. The WEP was significantly higher in the low cadence trial
(16.2 ± 4.4 kJ) and lower in the high cadence trial (12.9 ± 3.6 kJ) than in the standard test (14.2 ± 3.7 kJ). Thus, EP is
robust to the manipulation of power profile but is reduced by adopting cadences higher than âstandardâ. While the WEP is robust
to initial pacing applied, it is sensitive to even relatively minor changes in cadence.
The volatile organic compound (VOC) fluxes of living plant compartments other than foliage are poorly known. In this paper we describe for the first time the methanol and monoterpene fluxes from ...living Scots pine stems in situ, over 4 years at the SMEAR II station in southern Finland. The VOC fluxes from stems were measured online with an automated chamber measurement system. Both methanol and monoterpene emissions showed strong diurnal and seasonal cycles. Methanol emission rates were highest in mid-summer, and coincided with the most intensive period of stem radial growth. Methanol emission rates correlated moderately with the xylem sap flow rate and foliage transpiration rate, which suggests that many simultaneous and overlapping processes are related to methanol transport and production in trees. Monoterpene emissions from stems were highest on the hottest summer days, but also substantial in winter during times when the temperature was above zero °C for several days. Overall, the emissions from stems constitute about 2% of the whole stand monoterpene emissions under normal, non-stressed conditions. This can be used in stand monoterpene emission models as the rough estimate of woody compartment contribution.
: The hyperbolic form of the power-duration relationship is rigorous and highly conserved across species, forms of exercise, and individual muscles/muscle groups. For modalities such as cycling, the ...relationship resolves to two parameters, the asymptote for power (critical power CP) and the so-called W' (work doable above CP), which together predict the tolerable duration of exercise above CP. Crucially, the CP concept integrates sentinel physiological profiles-respiratory, metabolic, and contractile-within a coherent framework that has great scientific and practical utility. Rather than calibrating equivalent exercise intensities relative to metabolically distant parameters such as the lactate threshold or V˙O2max, setting the exercise intensity relative to CP unifies the profile of systemic and intramuscular responses and, if greater than CP, predicts the tolerable duration of exercise until W' is expended, V˙O2max is attained, and intolerance is manifested. CP may be regarded as a "fatigue threshold" in the sense that it separates exercise intensity domains within which the physiological responses to exercise can (<CP) or cannot (>CP) be stabilized. The CP concept therefore enables important insights into 1) the principal loci of fatigue development (central vs. peripheral) at different intensities of exercise and 2) mechanisms of cardiovascular and metabolic control and their modulation by factors such as O2 delivery. Practically, the CP concept has great potential application in optimizing athletic training programs and performance as well as improving the life quality for individuals enduring chronic disease.
PDF
