Durability of the moderate-to-heavy-intensity transition is related to the effects of prolonged exercise on severe-intensity performance

Purpose: Power output at the moderate-to-heavy intensity transition decreases during prolonged exercise. Resilience to this has been termed ‘durability’. The relationship between durability and performance, and the mechanistic determinants of durability, are not well-characterised. The purpose of this study was to assess the relationship between durability and the effect of prolonged exercise on severe-intensity performance, and explore intramuscular correlates of durability. Methods: On separate days, thirteen well-trained cyclists and triathletes (V̇O2peak, 57.3 ± 4.8 mL.kg-1.min-1; training volume, 12 ± 2.1 h.week-1) undertook an incremental test and 5-min time trial (TT) to determine power output at the first ventilatory threshold (VT1) and severe-intensity performance, with and without 150-min of prior moderate-intensity cycling. A single resting vastus lateralis microbiopsy was obtained.Results: Prolonged exercise reduced power output at VT1 (211 ± 40 vs. 198 ± 39 W, ∆ -13 ± 16 W, ∆ -6 ± 7%, P = 0.013) and 5-min TT performance (333 ± 75 vs. 302 ± 63 W, ∆ -31 ± 41 W, ∆ -9 ± 10%, P = 0.017). The reduction in 5-min TT performance was significantly associated with durability of VT1 (rs = 0.719, P = 0.007). Durability of VT1 was not related to vastus lateralis carnosine content, citrate synthase activity, or complex l activity (P > 0.05). Conclusion: These data provide the first direct support that durability of the moderate-to-heavy intensity transition is an important performance parameter. We did not find relationships between durability and vastus lateralis carnosine content, citrate synthase activity, or complex l activity

Thermo-behavioural responses to orally applied l-menthol exhibit sex-specific differences during exercise in a hot environment

AimsThis study investigated the efficacy of L-menthol mouth-rinsing on thermal sensation and perceived effort in females and males, using a fixed-rating of perceived exertion (RPE) exercise protocol in a hot environment.MethodsTwenty-two participants (eleven females, eleven males) completed two trials using a fixed-RPE protocol at an exercise intensity between ‘hard’ and ‘very hard’, equating to 16 on the RPE scale at ∼35°C. Participants adjusted power output to maintain RPE-16. In a randomised, double-blind, crossover design, L-menthol or a control mouthwash was administered at an orally neutral temperature (∼32 °C) prior to exercise and at 10 min intervals thereafter. Measures of mechanical power output, core temperature, heart rate, perception of thermal sensation and thermal comfort, and whole-body sweat loss are reported.ResultsThermal sensation was lowered by L-menthol in both sexes (P 0.05). No differences in exercise duration were observed compared to control, despite a ∼4 % and ∼6 % increase in male and females respectively. Power output increased by ∼6.5 % males (P = 0.039) with no difference in females ∼2.2% (P = 0.475), compared to control. Core temperature, heart rate and whole-body sweat loss was not different between condition or sex.ConclusionsL-menthol lowered perceptual measures of thermal sensation in females, but did not attenuate a greater rate of rise in thermal sensitivity when exercising in a hot environment, compared to males. Males appeared to adopt a higher risk strategy by increasing power output following L-menthol administration in contrast to a more conservative pacing strategy in females. Therefore, there appear to be sex-specific differences in L-menthol's non-thermal cooling properties and subsequent effects on thermo-behavioural adjustments in work-load when exercising in a hot environment

Advanced resistance training strategies for increasing muscle hypertrophy and maximal strength: part 1 accumulation methods

Training variation has been suggested as a primary principle in the pursuit of increasing muscle hypertrophy and maximal strength. Although variation may be achieved in a number of different manners within the training process, at the training session level advanced approaches to stimulating adaptations can be employed. At present, research is undecided on the benefits of these methods. Part 1 of this two-part article will review methods that may be employed to accumulate greater training volume through raising training density. Part 2 will discuss advance strategies that possess the potential to increase training intensity, while maintaining other acute exercise variables. The practical application of these methods will also be discussed, in the context of creating greater muscle cross-sectional area and developing maximal strength

Concurrent adaptations in maximal aerobic capacity, heat tolerance, microvascular blood flow and oxygen extraction following heat acclimation and ischemic preconditioning

We investigated the effects of: 1) Ischemic pre-conditioning (IPC) plus a concurrent five-day heat acclimation + IPC (IPC + HA), 2) five-day HA with sham IPC (HA), or 3) control (CON) on thermoneutral measurements of endurance performance, resting measures of skeletal muscle oxygenation and blood flow. Twenty-nine participants were randomly allocated to three groups, which included: 1) five-days of repeated leg occlusion (4 x 5-min) IPC at limb occlusive pressure, plus fixed-intensity (55% O2max) cycling HA at ∼36 °C/40% humidity; 2) HA plus sham IPC (20 mmHg) or 3) or CON (thermoneutral 55% O2max plus sham IPC). In IPC + HA and HA, there were increases in maximal oxygen consumption (O2max) (7.8% and 5.4%, respectively; P  0.05). Changes (P  0.05). Five-days of either HA or IPC + HA can enhance markers of endurance performance in cooler environments, alongside improved muscle oxygen extraction, blood flow, exercising muscle efficiency and O2 pulse at higher intensities, thus suggesting the occurrence of peripheral adaptation. Both HA and IPC + HA enhance the adaptation of endurance capacity, which might partly relate to peripheral changes

Repeated Ischemic Preconditioning Effects on Physiological Responses to Hypoxic Exercise

Introduction Repeated ischemic preconditioning (IPC) can improve muscle and pulmonary oxygen on-kinetics, blood flow and exercise efficiency but these effects have not been investigated severe hypoxia. The aim of the current study was to evaluate the effects of 7 d of IPC on resting and exercising muscle and cardio-pulmonary responses to severe hypoxia. Methods Fourteen subjects received either: 1) 7 d of repeated lower-limb occlusion (4 x 5 min, 217±30 mm Hg) at limb occlusive pressure (IPC) or SHAM (4 x 5 min, 20 mm Hg). Subjects were tested for resting limb blood flow (72), relative microvascular deoxyhemoglobin concentration ([HHB]) and pulmonary oxygen (V ̇O2p) responses to steady state and incremental exercise to exhaustion in hypoxia (fractional inspired O2 = 0.103), which was followed by 7 d of IPC or SHAM, and retesting 72 h post intervention. Results There were no effects of IPC on maximal oxygen consumption, time to exhaustion during the incremental test or minute ventilation and arterial oxygen saturation. However, the IPC group had higher delta efficiency based on pooled results and lower steady state delta[HHB] (IPC ~24% vs. SHAM ~6% pre-to-post), as well as slowing the [HHB] time constant (IPC ~26% vs. SHAM ~3% pre-to-post) and reducing the overshoot in [HHB]:V ̇O2 ratio during exercise onset. Conclusions Collectively, these results demonstrate that muscle O2 efficiency and microvascular O2 distribution can be improved by repeated IPC but there are no effects on maximal exercise capacity in a severe hypoxia

Predicting middle-distance track and cross-country performances of national and international level adolescent runners

This study evaluated the contribution of physiological data collected during laboratory testing in predicting race performances of trained junior middle-distance track (TK) and cross-country (XC) athletes. Participants performed a submaximal incremental ramp test, followed by an incremental test to exhaustion in a laboratory, with the results used to predict either 800 m TK, 1500 m TK or 4000-6000 m XC race performance. Twenty-eight participants (male (M), 15; female (F), 13) were analysed (age = 17 ± 2 years, height = 1.72 ± 0.08 m, body mass = 58.9 ± 8.9 kg). Performance times (min:s) for 800 m were: M, 1:56.55 ± 0:05.55 and F, 2:14.21 ± 0:03.89; 1500 m: M, 3:51.98 ± 0:07.35 and F 4:36.71 ± 0:16.58; XC: M (4900 ± 741 m), 16:00 ± 01:53; F (4628 ± 670 m), 17:41 ± 02:09. Stepwise regression analysis indicated significant contributions of speed at V̇O2max (sV̇O2max), and heart rate maximum (HRmax) to the prediction of 800 m TK (F(2,15) = 22.51, p <0.001, adjusted R2 = 0.72), sV̇O2max for 1500 m TK (F(1,13) = 36.65, p <0.001, adjusted R2 = 0.72) and V̇O2max, allometrically scaled to body mass and speed at lactate threshold (sLT) for XC (F(2,17) = 25.1, p <0.001, adjusted R2 = 0.72). Laboratory-based physiological measures can explain 72% of the variance in junior TK and XC events, although factors that explain performance alter depending on the race distance and tactics. The factors determining performance in TK and XC events are not interchangeable

Genetic Variation in the IL-6 and HLA-DQB1 Genes Is Associated with Spontaneous Clearance of Hepatitis C Virus Infection.

Background. Millions of people are infected with hepatitis C virus (HCV) worldwide and 30% spontaneously clear the infection. Reasons for HCV clearance without antiviral treatment are not well understood. Methods. Blood was collected for DNA analysis from patients with chronic HCV infection or evidence of spontaneous clearance. To overcome anticipated limitations of small sample size, primary analyses consisted of a candidate gene analysis of 12 preselected genes based on known association with host immunologic response to HCV infection. To further reduce the impact of multiple testing on power, a single likelihood ratio test was conducted for each gene using all associated SNPs assayed on the Illumina Quad 610/660W chip. Step-down permutation methods were used to adjust for multiple testing in all analyses. Results. Ninety-five and 62 patients with HCV chronic infection or spontaneous clearance, respectively, were included for analysis. HLA-DQB1 (p = 1.76⁎10(-5)) and IL-6 (p = 0.0007) genes were significantly associated with spontaneous HCV clearance. IL-28B was not significantly associated with spontaneous clearance (p = 0.17). Conclusion. Our whole-gene analytic strategy identified a previously unreported association of IL-6 with spontaneous clearance of HCV infection. We also confirmed the finding that HLA-DQB1 is associated with spontaneous resolution of HCV infection

Exercise tolerance during flat over-ground intermittent running: modelling the expenditure and reconstitution kinetics of work done above critical power

PurposeWe compared a new locomotor-specific model to track the expenditure and reconstitution of work done above critical power (W´) and balance of W´ (W´BAL) by modelling flat over-ground power during exhaustive intermittent running.MethodNine male participants completed a ramp test, 3-min all-out test and the 30–15 intermittent fitness test (30–15 IFT), and performed a severe-intensity constant work-rate trial (SCWR) at the maximum oxygen uptake velocity (vV̇O2max). Four intermittent trials followed: 60-s at vV̇O2max + 50% Δ1 (Δ1 = vV̇O2max − critical velocity [VCrit]) interspersed by 30-s in light (SL; 40% vV̇O2max), moderate (SM; 90% gas-exchange threshold velocity [VGET]), heavy (SH; VGET + 50% Δ2 [Δ2 = VCrit − VGET]), or severe (SS; vV̇O2max − 50% Δ1) domains. Data from Global Positioning Systems were derived to model over-ground power. The difference between critical and recovery power (DCP), time constant for reconstitution of W´ (τW′), time to limit of tolerance (TLIM), and W´BAL from the integral (W´BALint), differential (W´BALdiff), and locomotor-specific (OG-W´BAL) methods were compared.ResultsThe relationship between τW′ and DCP was exponential (r2 = 0.52). The τW′ for SL, SM, and SH trials were 119 ± 32-s, 190 ± 45-s, and 336 ± 77-s, respectively. Actual TLIM in the 30–15 IFT (968 ± 117-s) compared closely to TLIM predicted by OG-W´BAL (929 ± 94-s, P > 0.100) and W´BALdiff (938 ± 84-s, P > 0.100) but not to W´BALint (848 ± 91-s, P = 0.001).ConclusionThe OG-W´BAL accurately tracked W´ kinetics during intermittent running to exhaustion on flat surfaces