1,721,253 research outputs found
Sex differences in fatigability following exercise normalised to the power-duration relationship
No full textDue to morphological differences, females demonstrate greater fatigue resistance of locomotor muscle during single‐limb and whole‐body exercise modalities. Whilst females sustain a greater relative intensity of single‐limb, isometric exercise than males, limited investigation has been performed during whole‐body exercise. Accordingly, this study established the power–duration relationship during cycling in 18 trained participants (eight females). Subsequently, constant‐load exercise was performed at critical power (CP)‐matched intensities within the heavy and severe domains, with the mechanisms of fatigability assessed via non‐invasive neurostimulation, near‐infrared spectroscopy and pulmonary gas exchange during and following exercise. Relative CP (72 ± 5 vs. 74 ± 2% Pmax, P = 0.210) and curvature constant (51 ± 11 vs. 52 ± 10 J Pmax−1, P = 0.733) of the power–duration relationship were similar between males and females. Subsequent heavy (P = 0.758) and severe intensity (P = 0.645) exercise time to task failures were not different between sexes. However, females experienced lesser reductions in contractile function at task failure (P ≤ 0.020), and greater vastus lateralis oxygenation (P ≤ 0.039) during both trials. Reductions in voluntary activation occurred following both trials (P < 0.001), but were less in females following the heavy trial (P = 0.036). Furthermore, during the heavy intensity trial only, corticospinal excitability was reduced at the cortical (P = 0.020) and spinal (P = 0.036) levels, but these reductions were not sex‐dependent. Other than a lower respiratory exchange ratio in the heavy trial for females (P = 0.039), no gas exchange variables differed between sexes (P ≥ 0.052). Collectively, these data demonstrate that whilst the relative power–duration relationship is not different between males and females, the mechanisms of fatigability during CP‐matched exercise above and below CP are mediated by se
Intensity-dependent Contribution of Neuromuscular Fatigue after Constant-Load Cycling
Get PDFPurpose: We tested the hypothesis that central and peripheral fatigue after constant-load cycling exercise would vary with exercise intensity and duration.
Methods: Twelve well-trained male cyclists (V·O2max, 4.49 ± 0.35 L·min-1) completed three constant-load cycling trials to the limit of tolerance in a randomized crossover design. Exercise intensities were set according to the respiratory responses to a preliminary ramp test to elicit cardiorespiratory and metabolic responses consistent with exercise in the severe and heavy exercise domains: 1) at power at V·O2max (S+, 379 ± 31 W), 2) at 60% of the difference between gas exchange threshold and V·O2max (S-, 305 ± 23 W), and 3) at the respiratory compensation point (RCP, 254 ± 26 W). Pre- and postexercise twitch responses from the quadriceps to the electrical stimulation of the femoral nerve and magnetic stimulation of the motor cortex were recorded to assess neuromuscular and corticospinal function, respectively.
Results: Exercise time was 3.14 ± 0.59, 11.11 ± 1.86, and 42.14 ± 9.09 min for S+, S-, and RCP, respectively. All trials resulted in similar reductions in maximum voluntary force (P = 0.61). However, the degree of peripheral fatigue varied in an intensity-dependent manner, with greater reductions in potentiated twitch force after S+ (-33% ± 9%) compared with both S- (-16% ± 9%, P < 0.001) and RCP trials (-11% ± 9%, P < 0.001) and greater after S- compared with RCP (P < 0.05). For central fatigue, this trend was reversed, with smaller reductions in voluntary activation after S+ compared with RCP (-2.7% ± 2.2% vs –9.0% ± 4.7%, P < 0.01).
Conclusion: These data suggest the magnitude of peripheral and central fatigue after locomotor cycling exercise is exacerbated with exercise intensity and duration, respectively
The exercise intensity at maximal oxygen uptake (i⩒O2max): Methodological issues and repeatability
No full textThe minimum exercise intensity that elicits ⩒O2max (i⩒O2max) is an important variable associated with endurance exercise performance. i⩒O2max is usually determined during a maximal incremental exercise test; however, the magnitude and duration of the increments used influence the i⩒O2max value produced by a given test. The aims of this study were twofold. The first was to investigate whether the i⩒O2max value produced by a single cycle ergometer test (i⩒O2max(S)) was repeatable. The second was to determine if i⩒O2max(S) represents the minimum intensity at which ⩒O2max is elicited when compared to a refined i⩒O2max value (i⩒O2max(R)) derived from repeated tests. Seventeen male cyclists (age 33.9 ± 7.7 years, body mass 80.9 ± 10.2 kg, height 1.82 ± 0.05 m; VO2max 4.27 ± 0.62 L min−1) performed four maximal incremental tests for the determination of i⩒O2max(S) and i⩒O2max(R) (3 min stages; 20 W increments). Trials 1 and 2 were identical and used for assessing the repeatability of i⩒O2max(S), trials 3 and 4 began at different intensities and were used to determine i⩒O2max(R). i⩒O2max(S) showed good test–retest repeatability for i⩒O2max (CV = 4.1%; ICC = 0.93), VO2max (CV = 6.3%; ICC = 0.88) and test duration (CV = 6.7%; ICC = 0.89). There was no significant difference between i⩒O2max(S) and i⩒O2max(R) (303 ± 40 W vs. 301 ± 42 W) (P < .05). The present results suggest that i⩒O2max determined directly during a maximal incremental test is repeatable and provides a very good estimate of the minimum exercise intensity that elicits ⩒O2max
Ipsilateral corticomotor responses are confined to the homologous muscle following cross-education of muscular strength
No full textCross-education of strength occurs when strength-training 1 limb increases the strength of the untrained limb and is restricted to the untrained homologous muscle. Cortical circuits located ipsilateral to the trained limb might be involved. We used transcranial magnetic stimulation (TMS) to determine the corticomotor responses from the untrained homologous (biceps brachii) and nonhomologous (flexor carpi radialis) muscle following strength-training of the right elbow flexors. Motor evoked potentials were recorded from the untrained left biceps brachii and flexor carpi radialis during a submaximal contraction from 20 individuals (10 women, 10 men; aged 18–35 years; training group, n = 10; control group, n = 10) before and after 3 weeks of strength-training the right biceps brachii at 80% of 1-repetition maximum. Recruitment-curves for corticomotor excitability and inhibition of the untrained homologous and nonhomologous muscle were constructed and assessed by examining the area under the recruitment curve. Strength-training increased strength of the trained elbow flexors (29%), resulting in an 18% increase in contralateral strength of the untrained elbow flexors (P 0.05). These findings show that the cross-education of muscular strength is spatially distributed; however, the neural adaptations are confined to the motor pathway ipsilateral to the untrained homologous agonis
Optimization of Exercise Countermeasures for Human Space Flight: Operational Considerations for Concurrent Strength and Aerobic Training
Get PDFThe physiological challenges presented by space flight and in microgravity (μG) environments are well documented. μG environments can result in declines muscle mass, contractile strength, and functional capabilities. Previous work has focused on exercise countermeasures designed to attenuate the negative effects of μG on skeletal muscle structure, function, and contractile strength and aerobic fitness parameters. Exposure to μG environments influences both strength and aerobic type physical qualities. As such, the current exercise recommendations for those experiencing μG involve a combination of strength and aerobic training or “concurrent training.” Concurrent training strategies can result in development and maintenance of both strength and aerobic capabilities. However, terrestrial research has indicated that if concurrent training strategies are implemented inappropriately, strength development can be inhibited. Previous work has also demonstrated that the aforementioned inhibition of strength development is dependent on the frequency of aerobic training, modality of aerobic training, the relief period between strength and aerobic training, and the intra-session sequencing of strength and aerobic training. While time constraints and feasibility are important considerations for exercise strategies in μG, certain considerations could be made when prescribing concurrent strength and aerobic training to those experiencing human space flight. If strength and aerobic exercise must be performed in close proximity, strength should precede aerobic stimulus. Eccentric strength training methods should be considered to increase mechanical load and reduce metabolic cost. For aerobic capacity, maintenance cycle and/or rowing-based high-intensity intermittent training (HIIT) should be considered and cycle ergometry and/or rowing may be preferable to treadmill running
Transcranial magnetic stimulation in sport science: a commentary
Get PDFThe aim of this commentary is to provide a brief overview of transcranial magnetic stimulation (TMS) and highlight how this technique can be used to investigate the acute and chronic responses of the central nervous system to exercise.
We characterise the neuromuscular responses to TMS and discuss how these measures can be used to investigate the mechanisms of fatigue in response to locomotor exercise. We also discuss how TMS might be used to study the corticospinal adaptations to resistance exercise training, with particular emphasis on the responses to shortening/lengthening contractions and contralateral training. The limited data to date suggest that TMS is a valuable technique for exploring the mechanisms of central fatigue and neural adaptation
The effects of beetroot juice supplementation on indices of muscle damage following eccentric exercise.
No full textPurpose - Foods rich in antioxidant and anti-inflammatory phytochemicals might attenuate skeletal muscle damage; thus, the present study investigated whether consuming an antioxidant rich beetroot juice would attenuate the muscle-damaging effects of eccentric exercise.
Methods - Using a double blind, independent groups design, 30 recreationally active males were allocated to consume a high dose of beetroot juice (H-BT; 250 ml), a lower dose of beetroot juice (L-BT; 125 ml), or an isocaloric placebo (PLA; 250 ml) immediately (×3 servings), 24 (×2 servings) and 48 h (×2 servings) following completion of 100-drop jumps. Maximal isometric voluntary contractions (MIVC), countermovement jumps (CMJ), pressure pain threshold (PPT), creatine kinase (CK), interleukin-6 (IL-6), interleukin-8 (IL-8) and tumour necrosis factor-α (TNF-α) were measured pre, post, 2 (blood indices only), 24, 48 and 72 h following the drop jumps.
Results - CMJ performance recovered quicker (relative to baseline) in H-BT vs. PLA at 48 (91.7 ± 12.2 vs. 74.4 ± 17.3 %; P = 0.009, ES = 1.00) and 72 h postexercise (93.4 ± 7.7 vs. 86 ± 5.9 %; P = 0.046, ES = 1.25). PPT was greater in both the H-BT and L-BT vs. PLA at 24, 48 and 72 h postexercise (P 0.05).
Conclusions - Acute beetroot juice supplementation attenuated muscle soreness and decrements in CMJ performance induced by eccentric exercise; further research on the anti-inflammatory effects of beetroot juice are required to elucidate the precise mechanisms
Effects of exercise on alterations in redox homeostasis in elite male and female endurance athletes using a clinical point-of-care test
No full textExercise causes alterations in redox homeostasis (ARH). Measuring ARH in elite athletes may aid in the identification of training tolerance, fatigued states, and underperformance. To the best of our knowledge, no studies have examined ARH in elite male and female distance runners at sea level. The monitoring of ARH in athletes is hindered by a lack of reliable and repeatable in-the-field testing tools and by the rapid turnaround of results. We examined the effects of various exercise intensities on ARH in healthy (non-over-reached) elite male and female endurance athletes using clinical point-of-care (POC) redox tests, referred to as the free oxygen radical test (FORT) (pro-oxidant) and the free oxygen radical defence (FORD) (antioxidant). Elite male and female endurance athletes (n = 22) completed a discontinuous incremental treadmill protocol at submaximal running speeds and a test to exhaustion. Redox measures were analyzed via blood sampling at rest, warm-up, submaximal exercise, exhaustion, and recovery. FORD was elevated above rest after submaximal and maximal exercise, and recovery (p 0.05). The velocity at lactate threshold (vLT) correlated with the FORD response at rest, maximal exercise, and recovery (p < 0.05). Using the clinical POC redox test, an absence of oxidative stress after exhaustive exercise is evident in the nonfatigued elite endurance athlete. The blood antioxidant response (FORD) to exercise appears to be related to a key marker of aerobic fitness: vLT
The assessment of neuromuscular fatigue during 120 min of simulated soccer exercise
Get PDFPurpose
This investigation examined the development of neuromuscular fatigue during a simulated soccer match incorporating a period of extra time (ET) and the reliability of these responses on repeated test occasions.
Methods
Ten male amateur football players completed a 120 min soccer match simulation (SMS). Before, at half time (HT), full time (FT), and following a period of ET, twitch responses to supramaximal femoral nerve and transcranial magnetic stimulation (TMS) were obtained from the knee-extensors to measure neuromuscular fatigue. Within 7 days of the first SMS, a second 120 min SMS was performed by eight of the original ten participants to assess the reliability of the fatigue response.
Results
At HT, FT, and ET, reductions in maximal voluntary force (MVC; −11, −20 and −27%, respectively, P ≤ 0.01), potentiated twitch force (−15, −23 and −23%, respectively, P < 0.05), voluntary activation (FT, −15 and ET, −18%, P ≤ 0.01), and voluntary activation measured with TMS (−11, −15 and −17%, respectively, P ≤ 0.01) were evident. The fatigue response was robust across both trials; the change in MVC at each time point demonstrated a good level of reliability (CV range 6–11%; ICC2,1 0.83–0.94), whilst the responses identified with motor nerve stimulation showed a moderate level of reliability (CV range 5–18%; ICC2,1 0.63–0.89) and the data obtained with motor cortex stimulation showed an excellent level of reliability (CV range 3–6%; ICC2,1 0.90–0.98).
Conclusion
Simulated soccer exercise induces a significant level of fatigue, which is consistent on repeat tests, and involves both central and peripheral mechanism
Heart rate and indirect blood pressure responses to four different field anesthetic protocols in wild-born captive chimpanzees (Pan troglodytes)
No full textLimited data are available on hemodynamic responses to anesthetic protocols in wild-born chimpanzees (Pan troglodytes). Accordingly, this study characterized the heart rate (HR) and blood pressure responses to four anesthetic protocols in 176 clinically healthy, wild-born chimpanzees undergoing routine health assessments. Animals were anesthetized with medetomidine–ketamine (MK) (n = 101), tiletamine–zolazepam (TZ) (n = 30), tiletamine–zolazepam–medetomidine (TZM) (n = 24), or medetomidine–ketamine (maintained with isoflurane) (MKI) (n = 21). During each procedure, HR, systolic blood pressure (SBP), and diastolic blood pressure (DBP) were regularly recorded. Data were grouped according to anesthetic protocol, and mean HR, SBP, and DBP were calculated. Differences between mean HR, SBP, and DBP for each anesthetic protocol were assessed using the Kruskall–Wallis test and a Dunn multiple comparisons post hoc analysis. To assess the hemodynamic time course response to each anesthetic protocol, group mean data (±95% confidence interval [CI]) were plotted against time postanesthetic induction. Mean HR (beats/min [CI]) was significantly higher in TZ (86 [80–92]) compared to MKI (69 [61–78]) and MK (62 [60–64]) and in TZM (73 [68–78]) compared to MK. The average SBP and DBP values (mm Hg [CI]) were significantly higher in MK (130 [126–134] and 94 [91–97]) compared to TZ (104 [96–112] and 58 [53–93]) and MKI (113 [103–123] and 78 [69–87]) and in TZM (128 [120–135] and 88 [83–93]) compared to TZ. Time course data were markedly different between protocols, with MKI showing the greatest decline over time. Both the anesthetic protocol adopted and the timing of measurement after injection influence hemodynamic recordings in wild-born chimpanzees and need to be considered when monitoring or assessing cardiovascular healt
- …
