European Journal of Applied Physiology最新文献

Purpose: The aim of this study was to test the hypothesis that using threshold-based high intensity interval training (HIIT_THR) prescribed at an intensity above critical power (CP) in males and females matched for maximal oxygen uptake ( $\dot{\text{V}}$ O₂max) (mL/kg lean mass/min) will yield no sex differences in time to fatigue.

Methods: Thirteen males (mean ± SD: 22.0 ± 2.48 years, 181 ± 8.36 cm, 78.8 ± 11.4 kg) and eleven females (mean ± SD: 22.4 ± 2.69 years, 170 ± 5.73 cm, 65.2 ± 7.66 kg) initially undertook an incremental test to exhaustion to determine $\dot{\text{V}}$ O₂max, and a CP test. Then, one HIIT session (4 min on, 2 min off) was performed to exhaustion at the work rate associated with 105%CP. Acute physiological and cardiovascular responses were recorded.

Results: No sex differences were recorded in time to fatigue [Female vs. Male (min): 36.0 ± 18.5 vs. 39.3 ± 16.3], heart rate, rate of perceived exertion, or %oxygenated [haem]. Females displayed lower %deoxygenated [haem] at the end of interval 1, 2, 3, and 4 [Female vs. Male (%): 89.4 ± 21.2 vs. 110 ± 27.3, 92.0 ± 21.5 vs. 115 ± 27.6, 87.1 ± 23.7 vs. 112 ± 22.8, 88.9 ± 26.3 vs. 113 ± 23.5]. Large interindividual variability in performance, and physiological and perceptual response were present despite the use of threshold-based prescription.

Conclusion: The present study suggests that threshold-based prescription may help standardize the mean response exercise across sexes but does not eliminate physiological or perceptual variability. Furthermore, the lack of sex differences in TTF was accompanied by greater %deoxy[haem] in males, indicating tissue oxygenation is an unlikely determinant of HIIT performance. This study has been retrospectively registered at Trial Registration https://doi.org/10.17605/OSF.IO/KZVGC January 17th, 2023, following data collection but prior to data analyses.

Purpose: Recent studies suggest that, compared to healthy individuals, people with chronic obstructive pulmonary disease (pwCOPD) present a reduced capacity to perform cognitive-motor dual-task (CMDT). However, these studies were focused on short-duration CMDT offering limited insight to prolonged CMDT inducing fatigue, which can be encountered in daily life. The present study aimed to explore the effect of adding a cognitive task during repeated muscle contractions on muscle endurance, neuromuscular fatigability, and cognitive control in pwCOPD compared to healthy participants.

Methods: Thirteen pwCOPD and thirteen age- and sex-matched healthy participants performed submaximal isometric contractions of the knee extensors until exhaustion in two experimental sessions: (1) without cognitive task and (2) with a concurrent working memory task (i.e., 1-back task). Neuromuscular fatigability (as well as central and peripheral components measured by peripheral magnetic stimulation), cognitive performance, and perceived muscle fatigue were assessed throughout the fatiguing tasks.

Results: Independently to the experimental condition, pwCOPD exhibited lower muscle endurance compared to healthy participants (p = 0.039), mainly explained by earlier peripheral fatigue and faster attainment of higher perceived muscle fatigue (p < 0.05). However, neither effect of cognitive task (p = 0.223) nor interaction effect (group × condition; p = 0.136) was revealed for muscle endurance. Interestingly, cognitive control was significantly reduced only in pwCOPD at the end of CMDT (p < 0.015), suggesting greater difficulty for patients with dual tasking under fatigue.

Conclusion: These findings provide novel insights into how and why fatigue develops in COPD in dual-task context, offering a rationale for including such tasks in rehabilitation programs.

Purpose: The effects of low-intensity exercise, heat-induced hypo-hydration and rehydration on maximal strength and the underlying neurophysiological mechanisms are not well understood.

Methods: To assess this, 12 participants took part in a randomised crossover study, in a prolonged (3 h) submaximal (60 W) cycling protocol under 3 conditions: (i) in 45 °C (achieving ~ 5% body mass reduction), with post-exercise rehydration in 2 h (RHY2), (ii) with rehydration across 24 h (RHY24), and (iii) a euhydrated trial in 25 °C (CON). Dependent variables included maximal voluntary contractions (MVC), maximum motor unit potential (M_MAX), motor evoked potential (MEP_RAW) amplitude and cortical silent period (cSP) duration. Blood-brain-barrier integrity was also assessed by serum Ubiquitin Carboxyl-terminal Hydrolase (UCH-L1) concentrations. All measures were obtained immediately pre, post, post 2 h and 24 h.

Results: During both dehydration trials, MVC (RHY2: p < 0.001, RHY24: p = 0.001) and MEP_RAW (RHY2: p = 0.025, RHY24: p = 0.045) decreased from pre- to post-exercise. MEP_RAW returned to baseline during RHY2 and CON, but not RHY24 (p = 0.020). MEP/M_MAX ratio decreased across time for all trials (p = 0.009) and returned to baseline, except RHY24 (p < 0.026). Increased cSP (p = 0.011) was observed during CON post-exercise, but not during RHY2 and RHY24. Serum UCH-L1 increased across time for all conditions (p < 0.001) but was not significantly different between conditions.

Conclusion: Our findings demonstrate an increase in corticospinal inhibition after exercise with fluid ingestion, but a decrease in corticospinal excitability after heat-induced hypo-hydration. In addition, low-intensity exercise increases peripheral markers of blood-brain-barrier permeability.

Purpose: There is sparse evidence in the literature that the combination of neuromuscular electrical stimulation (NMES) and motor imagery (MI) can increase corticospinal excitability more that the application of one or the other modality alone. However, the NMES intensity usually employed was below or at motor threshold, not allowing a proper activation of the whole neuromuscular system. This questions the effect of combined MI + NMES with higher intensities, closer to those used in clinical settings. The purpose here was to assess corticospinal excitability during either MI, NMES or a combination of both at different evoked forces.

Methods: Seventeen healthy participants were enrolled in one session consisting of 6 conditions targeting flexor carpi radialis muscle (FCR): rest, MI, NMES at 5% and 20% of maximal voluntary contraction (MVC) and MI and NMES performed simultaneously (MI + NMES). During each condition, corticospinal excitability was assessed by evoking MEP of FCR by using transcranial magnetic stimulation. Maximal M-wave (Mmax) was measured by using the stimulation of the median nerve.

Results: MEPs during MI were greater as compared to rest (P = 0.005). MEPs during MI were significantly lower than during MI + NMES at 5% (P = 0.02) and 20% (P = 0.001). Then, MEPs during NMES 5% was significantly lower than during MI + NMES 20% (P < 0.005).

Conclusion: The present study showed that MI + NMES increased corticospinal excitability more than MI alone. However, corticospinal excitability was not higher as the intensity increase during MI + NMES. Therefore, MI + NMES targeting FCR may not significantly increase the corticospinal excitability between different low-submaximal contractions intensities.

Purpose: The aim of this study was to investigate the effect of 300 intermittent countermovement jumps (CMJs) on the mechanical power distribution at the joints of the lower limbs and the influence of the upper body to explain vertical jump performance.

Methods: Fifteen male sport students (age 24.5 ± 2.3 years; body height 1.85 ± 0.06 m; body mass 84.8 ± 8.5 kg) performed a set of intermittent 300 CMJs at maximal effort. An inverse-dynamic approach was used to calculate the mechanical power at the hip, knee, and ankle joint for each jump.

Results: Jump height and mechanical power in the knee and ankle joints decreased significantly (p < .010), while remained the same in the hip joint. In contrast, a significant increased vertical velocity was observed for the upper body segment. In addition, a significant higher angular momentum at the center of mass was detected during the braking and propulsion phase.

Conclusion: The findings highlight a fatigue-related decrease in lower limb power, particularly in the knee and ankle joints, which changed the mechanical power distribution at the joints of the lower limbs. The trunk extensor muscles were probably able to counteract the fatigue-related decrease in lower limb power by increased vertical velocity of the upper body segment and higher angular momentum at the center of mass during the braking and propulsion phase. Accordingly, the most effective way to maintain jumping performance in fatigued state would be to improve the fatigue resistance of the knee extensors, ankle plantar flexors, and trunk extensor muscles.

Purpose: To analyze the influence of training status on the percentage of maximum oxygen consumption, heart rate and velocity (%VO_2max, %HR_max and %V_max) at which ventilatory threshold 1 and ventilatory threshold 2 occur (VT1 and VT2, respectively), in males and females separately considering age, during a ramp incremental treadmill test.

Methods: 791 males (36.8 ± 9.9 years) and 301 females (33.9 ± 11.0 years) performed a ramp incremental exercise test until fatigue where VT1 and VT2 were determined. Participants were classified as low, medium or high training status combining the oxygen consumption at VT1, VT2 and VO_2max by clustering analysis.

Results: VO_2max is poorly correlated with the %VO_2max, %HR_max and %V_max at which VT1 and VT2 occur (r < 0.3), in contrast, there is a positive correlation between oxygen consumption at VT1 and VT2 with the %VO_2max, %HR_max and %V_max at which VT1 and VT2, respectively, occur in males and females (r = 0.203-0.615). Furthermore, we observed the %VO_2max, %HR_max and %V_max at which thresholds occur were greater the higher the training status (all p < 0.003).

Conclusion: The physiological determinants of the percentage of maximum at which VT1 and VT2 occur are more related to oxygen consumption at VT1 and VT2, respectively, than to VO_2max. Moreover, due to the higher percentage of maximum at which VT1 and VT2 occur in individuals with a higher training status, the common strategy consisting of establishing exercise intensity as a fixed percentage of maximum might not be effective to match intensity across individuals with different training status.

Clinical trial registration: NCT06246760.

Background: Vestibulospinal reflexes play a role in maintaining the upright posture of the trunk. Head orientation has been shown to modify the vestibulospinal reflexes during standing. This study investigated how vestibular signals affect paraspinal muscle activity during walking, and whether head orientation changes these effects.

Methods: Sixteen participants were instructed to walk on a treadmill for 8 min at 78 steps/min and 2.8 km/h in four conditions defined by the presence of electrical vestibular stimulation (EVS) and by head orientation (facing forward and facing leftward), while bipolar electromyography (EMG) was recorded bilaterally from the paraspinal muscles from cervical to lumbar levels.

Results: In both head orientations, significant phasic EVS-EMG coherence in the paraspinal muscles was observed at ipsilateral and/or contralateral heel strikes. Compared to walking with the head forward, a significant decrease was found in EVS-evoked responses (i.e., EVS-EMG coherence and gain) when participants walked with the leftward head orientation, with which EVS induced disturbance in the sagittal plane. This overall decrease can be explained by less need of feedback control for walking stabilization in the sagittal plane compared to in the frontal plane. The decrease in coherence was only significant at the left lower vertebral levels and at the right upper vertebral levels around left heel strikes.

Conclusion: These findings confirm the contribution of the vestibular afferent signals to the control of paraspinal muscle activity during walking and indicate that this control is changed in response to different head orientations.

Purpose: The biochemical background of the (near-)linear direct relationship between the curvature constant (W') of the power-duration curve and the magnitude ( $\Delta {\dot{\text{V}}\text{O}}_{\text{2sc}}$ ) of the slow component of the ${\dot{\text{V}}\text{O}}_2$ on-kinetics ( ${\dot{\text{V}}\text{O}}_{\text{2sc}}$ ) as well as reverse relationship between critical power (CP) and the characteristic transition time (t_0.63, analogous to τ_p) of the primary phase II of the ${\dot{\text{V}}\text{O}}_2$ on-kinetics encountered in experimental studies is studied.

Methods: A computer model of the bioenergetic system in skeletal muscle, involving the each-step-activation mechanism of work transitions and P_i double-threshold mechanism of muscle fatigue, is used.

Results: The activity (rate constant) (k_add) of the additional ATP usage, underlying the slow component, determines to a large extent the (near-)linear direct W'- $\Delta {\dot{\text{V}}\text{O}}_{\text{2sc}}$ relationship, as an increase in k_add increases markedly both W' and $\Delta {\dot{\text{V}}\text{O}}_{\text{2sc}}$ . t_0.63 is a derivative of the changes in metabolite (M = PCr or Cr or P_i) concentrations between rest and the steady-state of the phase II M on-kinetics after the onset of exercise. The oxidative phosphorylation (OXPHOS) activity (k_OX) mostly determines the (near)-linear inverse CP-t_0.63 relationship, as an increase in k_OX markedly decreases ΔM and t_0.63, and elevates CP.

Conclusions: The ${\dot{\text{V}}\text{O}}_2$ on-kinetics (e.g., ${\dot{\text{V}}\text{O}}_{\text{2sc}}$ or t_0.63) cannot cause anything in the system, as it is an emergent property of the system functioning on the biochemical level. Physiological variables: muscle ${\dot{\text{V}}\text{O}}_{\text{2sc}}$ and W' as well as t_0.63 and CP, and relationships between them, are determined by biochemical parameters, mainly k_add and k_OX, respectively.