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1.
Upper-body dynamic and isometric maximum strength are essential components for success in Brazilian jiu-jitsu (BJJ). This study was aimed at analysing strength parameters in the elbow flexor and extensor muscles of BJJ practitioners. Participants (n = 28) performed maximum isometric contractions of elbow flexors and extensors to determine peak torque (PT), rate of force development (RFD), and the torque–angle (T–A) relationship at elbow angles of 45°, 60°, 75°, 90°, 105°, and 120°. Additionally, concentric and eccentric PTs were measured at 1.04 rad·s-1. Student t-test and ANOVA were performed using α = 0.05. Elbow flexors were stronger isometrically (P < 0.001, ES = 1.23) but weaker concentrically (P < 0.05, ES = 0.54) than extensor muscles, possibly because of the extensive grip disputes and pushing of opponents in BJJ. The T–A relationship had an inverted “U”-shape. Torque differences across elbow angles were moderate (ES = 0.62) for the extensor and large (ES = 0.92) for the flexor muscles. Isometric torque was greatest for elbow angles of 105° and 75° and smallest for 45° and 120° for extensor and flexor muscles, respectively. Elbow flexors had a greater RFD than extensors, regardless of elbow angle. The present study provides comprehensive results for elbow muscle strength in BJJ practitioners.  相似文献   

2.
Abstract

We investigated the effects of static stretch duration on peak isometric plantarflexor moment and passive ankle moment in seven healthy volunteers. After the passive ankle plantarflexor moment was recorded on an isokinetic dynamometer, the peak isometric ankle moment was measured with simultaneous electromyographic monitoring of the medial gastrocnemius. The participants subsequently performed a single 5-s stretch, a single 15-s stretch, four 5-s stretches, four 15-s stretches or no stretch (control) before being re-tested. All participants randomly completed each condition with a 24-h rest between tests. The main finding of the study was a significant correlation between reductions in peak moment and stretch duration (r=0.68; P<0.05), which became significantly different from the control group after four 15-s stretches (16.7%, s=5.3; P<0.05). There was a similar decrease in passive moment (20.9%, s=1.3; P<0.05) after each stretch condition, but this was not accompanied by a change in hysteresis. The electromyographic activity recorded during maximal plantarflexion did not change significantly after stretching. Our results are the first to show a duration-dependent effect of stretch on force (moment) production of the plantarflexors. Further research is required to elucidate the mechanisms responsible, as alterations in the stiffness properties of the muscle–tendon complex or muscle recruitment cannot completely explain the changes.  相似文献   

3.
Abstract

The objective of this study was to examine the effects of acute static muscle stretch on hamstring muscle fatigue and perceived exertion between young adult men and women. Twenty volunteers participated in two experimental sessions, in which we assessed maximal-effort isokinetic knee flexor force (90° · s?1) and the number of sub-maximal (50% maximal) knee flexor repetitions to the point of failure. Immediately before the sub-maximal contractions on one randomly selected session, participants received ten 30-s passive knee flexor muscle stretches. Perceived exertion was sampled with a modified Borg category-ratio scale following each sub-maximal repetition. Each participant's perceived exertion response was estimated every 10% across the sub-maximal repetitions, via linear interpolation and power-function modelling. The men generated significantly greater force than the women during both experimental sessions, while muscle stretching had no significant effect on the number of sub-maximal repetitions. When estimated via power-function modelling, perceived exertion increased at a significantly greater rate following muscle stretch. Perceived exertion was significantly greater for the women following muscle stretch than the men. The findings suggest that the elevation in perceived exertion following knee flexor muscle stretching may be greater in women than men, despite no significant alterations in mechanical measures of muscle fatigue.  相似文献   

4.
Two experiments (n = 10) were conducted to determine the effects of roller massager (RM) on ankle plantar flexor muscle recovery after exercise-induced muscle damage (EIMD). Experiment 1 examined both functional [i.e., ankle plantar flexion maximal isometric contraction and submaximal (30%) sustained force; ankle dorsiflexion maximal range of motion and resistance to stretch; and medial gastrocnemius pain pressure threshold] and morphological [cross-sectional area, thickness, fascicle length, and fascicle angle] variables, before and immediately, 1, 24, 48, and 72 h after an EIMD stimulus. Experiment 2 examined medial gastrocnemius deoxyhaemoglobin concentration kinetics before and 48 h after EIMD. Participants performed both experiments twice: with (RM) and without (no-roller massager; NRM) the application of a RM (6 × 45 s; 20-s rest between sets). RM intervention did not alter the functional impairment after EIMD, as well as the medial gastrocnemius morphology and oxygenation kinetics (P > 0.05). Although, an acute increase of ipsilateral (RM = + 19%, NRM = ?5%, P = 0.032) and a strong tendency for contralateral (P = 0.095) medial gastrocnemius pain pressure threshold were observed. The present results suggest that a RM has no effect on plantar flexors performance, morphology, and oxygenation recovery after EIMD, except for muscle pain pressure threshold (i.e., a soreness).  相似文献   

5.
Purpose: The aim of this study was to examine the effect of active versus passive recovery on 6 repeated Wingate tests (30-s all-out cycling sprints on a Velotron ergometer). Method: Fifteen healthy participants aged 29 (SD = 8) years old (body mass index = 23 [3] kg/m2) participated in 3 sprint interval training sessions separated by 3 to 7 days between each session during a period of 1 month. The 1st visit was familiarization to 6 cycling sprints; the 2nd and 3rd visits involved a warm-up followed by 6 30-s cycling sprints. Each sprint was followed by 4 min of passive (resting still on the ergometer) or active recovery (pedaling at 1.1 W/kg). The same recovery was used within each visit, and recovery type was randomized between visits. Results: Active recovery resulted in a 0.6 W/kg lower peak power output in the second sprint (95% confidence interval [CI] [ ? 0.2, ? 0.8 W/kg], effect size = 0.50, p < .01) and a 0.4 W/kg greater average power output in the 5th and 6th sprints (95% CI [+0.2,+0.6 W/kg], effect size = 0.50, p < .01) compared with passive recovery. There was little difference between fatigue index, total work, or accumulated work between the 2 recovery conditions. Conclusions: Passive recovery is beneficial when only 2 sprints are completed, whereas active recovery better maintains average power output compared with passive recovery when several sprints are performed sequentially (partial eta squared between conditions for multiple sprints = .38).  相似文献   

6.
Abstract

The purpose of this study was to establish whether critical power, as traditionally determined from the performance of three constant-load tests to exhaustion, is attained at the end of a 90-s all-out test in children. Sixteen healthy children (eight males and eight females; mean age 12.3 years, sx  = 0.1; body mass 39.6 kg, sx  = 1.8; peak [Vdot]O2 2.0 litres · min?1, sx  = 0.1) completed an incremental test to exhaustion to determine peak oxygen uptake (peak [Vdot]O2), three separate constant-load tests to exhaustion to calculate critical power, and an isokinetic 90-s all-out test. The end power of the 90-s test averaged over the last 10 s (140 W, sx  = 8) was significantly higher than critical power (105 W, sx  = 6; t = 6.8; P < 0.01), yet the two parameters were strongly correlated (r = 0.74; P < 0.01). After 60 s, there were no further reductions in power output during the 90-s test (P < 0.0001). In conclusion, at the end of a 90-s all-out test, children are able to produce power outputs well above critical power. This suggests that 90 s is not long enough to completely exhaust the anaerobic work capacity in children.  相似文献   

7.
Abstract

The purpose of this study was to determine the effects of plyometric exercise on unilateral balance performance. Nine healthy adults performed baseline measurements on the dominant limb that consisted of: a 20-s unilateral stability test on a tilt balance board, where a higher stability index represented deterioration in balance performance; isokinetic plantar flexion torque at 0.52 and 3.14 rad · s?1; muscle soreness in the calf region; and resting plantar flexion angle. Plyometric exercise consisted of 200 counter-movement jumps designed to elicit symptoms of muscle damage, after which baseline measurements were repeated at 30 min, 24, 48, and 72 h. Perceived muscle soreness of the calf region increased significantly following the plyometric exercise protocol (F4,32 = 17.24, P < 0.01). Peak torque was significantly reduced after the plyometric exercise protocol (F4,32 = 7.49, P < 0.05), with greater loss of force at the lower angular velocity (F4,32 = 3.46, P < 0.05), while resting plantar flexion angle was not significantly altered compared with baseline values (P > 0.05). The stability index was significantly increased (F4,32 = 3.10, P < 0.05) above baseline (mean 2.3, s = 0.3) at 24 h (3.3, s = 0.4), after which values recovered. These results indicate that there is a latent impairment of balance performance following a bout of plyometric exercise, which has implications for both the use of skill-based activities and for increased injury risk following high-intensity plyometric training.  相似文献   

8.
Abstract

The purpose of this study was to investigate the time course of the changes of muscle-tendon mechanical properties and the function responses of the plantar flexor muscles following 5?×?60?s of static stretching.

Fourteen healthy volunteers were tested on four separate days in a random order with three different rest times (0, 5, 10?min) after 5?×?60?s of stretching or following a control period without stretching. During each test, the dorsiflexion range of motion (RoM), passive resistive torque (PRT), and maximum voluntary contraction (MVC) were measured with a dynamometer. Ultrasonography of the gastrocnemius medialis (GM) muscle-tendon junction displacement and motion capture allowed us to determine the length changes in the tendon and muscle, respectively, and hence to calculate their stiffness.

We observed an increase in RoM and decrease in MVC at 0, 5, and 10?min post-stretching. This could be attributed to an increase in muscle elongation which lasted at least 10?min. A decrease in muscle-tendon stiffness was observed immediately, but not 5 or 10?min after the stretching. A decrease in PRT and muscle stiffness was observed up to 5?min after the stretching. No changes were detected in tendon stiffness or in any variable in the control group.

The effects of a 5?×?60?s static stretching exercise changes the muscle-tendon functions (RoM, MVC), which are related to mechanical changes of the muscle but not the tendon structure, respectively. Although the functional changes last for at least 10?min, changes in muscle stiffness were only observed up to 5?min after the stretching exercise.  相似文献   

9.
We examined the influence of stretching alone (SS) or combined with self-massage (SM) on maximal ankle dorsiflexion angle, maximal voluntary contraction (MVC) torque and calf muscle activity, and subcutaneous tissue thickness in 15 young (25 ± 3 years) and 15 middle-aged (45 ± 5 years) adults. Participants performed two sessions of calf muscle stretches (3x 30-s stretches, 30-s rest): stretch after a 60-s control condition (SS) and stretch after 60 s of self-massage with therapy balls (SM). Evaluations were performed before and 5 min after the intervention. Linear mixed effects model revealed no main effect for age on ROM or MVC and significant main effects for treatment and time. Change in ankle angle was greater after SM: SS = 3.1 ± 2°, SM = 6.2 ± 3.3° (Hedges’ g = 0.98, p < 0.001). Similar results were observed for MVC torque: SS = ?4 ± 16%, SM = 12 ± 16% (Hedges’ g = 0.97, p = 0.0001). Changes in MVC torque and absolute EMG amplitude were correlated, but subcutaneous tissue thickness was not altered by treatment. The gains in ROM were more pronounced in less flexible middle-aged adults, underscoring the need to include flexibility exercises in their training.  相似文献   

10.
Abstract

The aim of this study was to examine the effects of active versus passive recovery on blood lactate disappearance and subsequent maximal performance in competitive swimmers. Fourteen male swimmers from the University of Virginia swim team (mean age 20.3 years, s = 4.1; stature 1.85 m, s = 2.2; body mass 81.1 kg, s = 5.6) completed a lactate profiling session during which the speed at the lactate threshold (VLT), the speed at 50% of the lactate threshold (VLT.5), and the speed at 150% of the lactate threshold (VLT1.5) were determined. Participants also completed four randomly assigned experimental sessions that consisted of a 200-yard maximal-effort swim followed by 10 min of recovery (passive, VLT.5, VLT, VLT1.5) and a subsequent 200-yard maximal effort swim. All active recovery sessions resulted in greater lactate disappearance than passive recovery (P < 0.0001 for all comparisons), with the greatest lactate disappearance associated with recovery at VLT (P = 0.006 and 0.007 vs. VLT.5 and VLT1.5 respectively) [blood lactate disappearance was 2.1 mmol · l?1 (s = 2.0), 6.0 mmol · l?1 (s = 2.6), 8.5 mmol · l?1 (s = 1.8), and 6.1 mmol · l?1 (s = 2.5) for passive, VLT.5, VLT, and VLT1.5 respectively]. Active recovery at VLT and VLT1.5 resulted in faster performance on time trial 2 than passive recovery (P = 0.005 and 0.03 respectively); however, only active recovery at VLT resulted in improved performance on time trial 2 (TT2) relative to time trial 1 (TT1) [TT2?TT1: passive +1.32 s (s = 0.64), VLT.5+1.01 s (s = 0.53), VLT?1.67 s (s = 0.26), VLT1.5?0.07 s (s = 0.51); P < 0.0001 for VLT). In conclusion, active recovery at the speed associated with the lactate threshold resulted in the greatest lactate disappearance and in improved subsequent performance in all 14 swimmers. Our results suggest that coaches should consider incorporating recovery at the speed at the lactate threshold during competition and perhaps during hard training sessions.  相似文献   

11.
Muscle utilisation in squat exercise depends on technique. The purpose of this study was to compare net joint moments (NJMs) and muscle activation during squats without and with restricted leg dorsiflexion. Experienced men (n = 5) and women (n = 4) performed full squats at 80% one repetition maximum. 3D motion analysis, force platform and (EMG) data were collected. Restricting anterior leg rotation reduced anterior leg (P = 0.001) and posterior thigh (P < 0.001) rotations, resulting in a smaller knee flexion range of motion (P < 0.001). At maximum squat depth, ankle plantar flexor (P < 0.001) and knee extensor (P < 0.001) NJM were higher in unrestricted squats. Hip extensor NJM (P = 0.14) was not different between squat types at maximum squat depth. Vastus lateralis (P > 0.05), vastus medialis (P > 0.05) and rectus femoris (P > 0.05) EMG were not different between squat types. Unrestricted squats have higher ankle plantar flexor and knee extensor NJM than previously reported from jumping and landing. However, ankle plantar flexor and knee extensor NJM are lower in restricted squats than previous studies of jumping and landing. The high NJM in unrestricted squat exercise performed through a full range of motion suggests this squat type would be more effective to stimulate adaptations in the lower extremity musculature than restricted squats.  相似文献   

12.
Abstract

The metatarsal phalangeal joint (MPJ) and its crossing toe flexor muscles (TFM) represent the link between the large energy generating leg extensor muscles and the ground. The purpose of this study was to examine the functional adaptability of TFM to increased mechanical stimuli and the effects on walking, running and jumping performance.

Fifteen men performed a heavy resistance TFM strength training with 90% of the maximal voluntary isometric contraction (MVIC) for 7 weeks (560 contractions) for the left and right foot. Maximal MPJ and ankle plantar flexion moments during MVICs were measured in dynamometers before and after the intervention. Motion analyses (inverse dynamics) were performed during barefoot walking, running, and vertical and horizontal jumping. Athletic performance was determined by measuring jump height and distance.

Left (0.21 to 0.38 Nm · kg?1; P < 0.001) and right (0.24 to 0.40 Nm · kg?1; P < 0.001) MPJ plantar flexion moments in the dynamometer, external MPJ dorsiflexion moments (0.69 to 0.75 Nm · kg?1; P = 0.012) and jump distance (2.25 to 2.31 m; P = 0.006) in horizontal jumping increased significantly.

TFM responded highly to increased loading within a few weeks. The increased force potential made a contribution to an athlete's performance enhancement.  相似文献   

13.
This study aims to (1) determine whether isometric training at a short vs. long quadriceps muscle length affects concentric torque production; (2) examine the relationship between muscle hypertrophy and concentric torque; and (3) determine whether changes in fascicle length are associated with changes in concentric torque.

Sixteen men performed isometric training at a short (SL, n = 8) or a long muscle length (LL, n = 8). Changes in maximal concentric torque were measured at 30, 60, 90, 120, 180, 240 and 300 rad · s?1. The relationships between the changes in concentric torque, cross-sectional area, volume and fascicle length were tested.

Concentric torque increased significantly after training only in LL and at angular velocities of 30 and 120 rad · s?1 by 12–13% (P < 0.05). Muscle size increased in LL only, the changes were correlated (r = 0.73–0.93, P < 0.05) with the changes in concentric torque. Vastus lateralis (VL) fascicle length increased in both groups (5.4 ± 4.9%, P = 0.001) but the change was not correlated with changes in concentric torque in either group.

Isometric training-induced increases in muscle size and concentric torque were best elicited by training at long muscle lengths. These results highlight a clear muscle length dependence of isometric training on dynamic torque production.  相似文献   

14.
Previous studies suggested that a pronounced weakness of the extensor muscles relative to the flexor muscles could increase the risk of occurrence of lateral epicondylalgia. This study investigates this hypothesis by estimating the ratio of extensor to flexor muscle capacities among healthy non-players (n = 10), healthy tennis players (n = 20), symptomatic players (n = 6), and players who have recovered from lateral epicondylalgia (n = 6). Maximum net joint moments in flexion or extension were measured during seven tasks involving the voluntary contraction of wrist and fingers. Using these data, the muscle capacities of the main muscle groups of the hand (wrist flexors, wrist extensors, finger flexors, finger extensors, and intrinsic muscles) were estimated using a musculoskeletal model. These capacities were then used to compute the extensor/flexor capacity ratios about the wrist and the finger joints. Compared to healthy non-players, healthy players presented higher extensor muscle capacities and greater capacity ratios showing that playing tennis generates specific adaptations of muscle capacities. Interestingly, symptomatic players, similar to those of non-players, showed more imbalanced ratios than healthy players. These results confirm that the ratio of extensor/flexor muscle capacities seems to be associated with lateral epicondylalgia and can be further used to understand its incidence and consequences.  相似文献   

15.
Abstract

Eighteen male subjects, ages 20–28 years, engaged in three fatigue bouts using an isokinetic dynamometer (Cybex II). Maximum knee extension contractions were given for 100 s at a rate of 30 per minute. The three contraction speeds chosen were 120° · s –1 160° · s –1 and 200° · s –1.Peak torque at 120° · s –1 was significantly greater (p <.05) than at 200° · s –1 for the first 60 s, and 160° · s –1 for the first 50 s. Thereafter, no significant differences existed among conditions. All three curves were found to follow two-component exponential functions as shown by the equation yt =a 2 ek2t – a 1 ek1t + c. The three curves possessed similar rate constants for both components. Time to peak torque was achieved at similar times for testing at 160 and 200° · s –1 (p <.05). It is concluded that peak torque varies inversely with movement speed, and that the pattern of decrement is independent of movement speed. Time to peak torque does not appear to change significantly across trials in isokinetic fatigue.  相似文献   

16.
Abstract

The aim of this study was to determine if inducing metabolic alkalosis would alter neuromuscular control after 50 min of standardized submaximal cycling. Eight trained male cyclists (mean age 32 years, s = 7; [Vdot]O2max 62 ml · kg?1 · min?1, s = 8) ingested capsules containing either CaCO3 (placebo) or NaHCO3 (0.3 g · kg?1 body mass) in eight doses over 2 h on two separate occasions, commencing 3 h before exercise. Participants performed three maximal isometric voluntary contractions (MVC) of the knee extensors while determining the central activation ratio by superimposing electrical stimulation both pre-ingestion and post-exercise, followed by a 50-s sustained maximal contraction in which force, EMG amplitude, and muscle fibre conduction velocity were assessed. Plasma pH, blood base excess, and plasma HCO3 were higher (P < 0.01) during the NaHCO3 trial. After cycling, muscle fibre conduction velocity was higher (P < 0.05) during the 50-s sustained maximal contraction with NaHCO3 than with placebo (5.1 m · s?1, s = 0.4 vs. 4.2 m · s?1, s = 0.4) while the EMG amplitude remained the same. Force decline rate was less (P < 0.05) during alkalosis-sustained maximal contraction and no differences were shown in central activation ratio. These data indicate that induced metabolic alkalosis can increase muscle fibre conduction velocity following prolonged submaximal cycling.  相似文献   

17.
Downhill backwards walking causes repeated, cyclical loading of the muscle–tendon unit. The effect this type of repeated loading has on the mechanical behaviour of the Achilles tendon is presently unknown. This study aimed to investigate the biomechanical response of the Achilles tendon aponeurosis complex following a downhill backwards walking protocol. Twenty active males (age: 22.3 ± 3.0 years; mass: 74.7 ± 5.6 kg; height: 1.8 ± 0.7 m) performed 60 min of downhill (8.5°), backwards walking on a treadmill at ?0.67 m · s?1. Data were collected before, immediately post, and 24-, 48- and 168-h post-downhill backwards walking. Achilles tendon aponeurosis elongation, strain and stiffness were measured using ultrasonography. Muscle force decreased immediately post-downhill backward walking (P = 0.019). There were increases in Achilles tendon aponeurosis stiffness at 24-h post-downhill backward walking (307 ± 179.6 N · mm?1, P = 0.004), and decreases in Achilles tendon aponeurosis strain during maximum voluntary contraction at 24 (3.8 ± 1.7%, P = 0.008) and 48 h (3.9 ± 1.8%, P = 0.002) post. Repeated cyclical loading of downhill backwards walking affects the behaviour of the muscle–tendon unit, most likely by altering muscle compliance, and these changes result in tendon stiffness increases.  相似文献   

18.
Abstract

This study examined the effect of two different interval training programs–high-intensity interval training (HIT) and supramaximal interval training (SMIT)–on measures of sprint and endurance performance. Physically active individuals (Females: n=32; age 19.3, s=2.2 years; mass 67.6, s=9.1 kg; stature 172.7, s=6.6 cm. Males: n=23; age 20.0, s=2.7 years; mass 71.3, s=8.3 kg; stature 176.6, s=5.8 cm) completed pre-testing that comprised (1) 3000 m time-trial, (2) 40 m sprint, and (3) repeated sprint ability (RSA–6×40 m sprints, 24 s active recovery) performance. Participants were then matched for average 3000 m running velocity (AV) and randomly assigned to one of three groups: (i) HIT, n=19, 4 min at 100% AV, 4 min passive recovery, 4–6 bouts per session; (ii) SMIT, n=20, 30 s at 130% AV, 150 s passive recovery, 7–12 bouts per session; and (iii) control group, n=16, 30 min continuous running at 75% AV. Groups trained three times per week for six weeks. When time to complete each test were compared among groups: (i) improvements in 3000 m time trial performance were greater following SMIT than continuous running, and (ii) improvements in 40 m sprint and RSA performance were greater following SMIT than HIT and continuous running. In addition, a gender effect was observed for the 3000 m time trial only, where females changed more following the training intervention than males. In summary, for concurrent improvements in endurance, sprint and repeated sprint performance, SMIT provides the greatest benefits for physically active individuals.  相似文献   

19.
Abstract

The aim of the study was to examine several physiological responses to a climbing-specific task to identify determinants of endurance in sport rock climbing. Finger strength and endurance of intermediate rock climbers (n = 11) and non-climbers (n = 9) were compared using climbing-specific apparatus. After maximum voluntary contraction (MVC) trials, two isometric endurance tests were performed at 40% (s = 2.5%) MVC until volitional exhaustion (continuous contractions and intermittent contractions of 10 s, with 3 s rest between contractions). Changes in muscle blood oxygenation and muscle blood volume were recorded in the flexor digitorum superficialis using near infra-red spectroscopy. Statistical significance was set at P < 0.05. Climbers had a higher mean MVC (climbers: 485 N, s = 65; non-climbers 375 N, s = 91) (P = 0.009). The group mean endurance test times were similar. The force – time integral, used as a measure of climbing-specific endurance, was greater for climbers in the intermittent test (climbers: 51,769 N · s, s = 12,229; non-climbers: 35,325 N · s, s = 9724) but not in the continuous test (climbers: 21,043 N · s, s = 4474; non-climbers: 15,816 N · s, s = 6263). Recovery of forearm oxygenation during rest phases (intermittent test) explained 41.1% of the variability in the force – time integral. Change in total haemoglobin was significantly greater in non-climbers (continuous test) than climbers (P = 0.023 – 40% test timepoint, P = 0.014 – 60% test timepoint). Pressor responses were similar between groups and not related to the force – time integral for either test. We conclude that muscle re-oxygenation during rest phases is a predictor of endurance performance.  相似文献   

20.
Abstract

In this study, we examined the effects of different work:rest durations during 20 min intermittent treadmill running and subsequent performance. Nine males (mean age 25.8 years, s = 6.8; body mass 73.9 kg, s = 8.8; stature 1.75 m, s = 0.05; [Vdot]O2max 55.5 ml · kg?1 · min?1, s = 5.8) undertook repeated sprints at 120% of the speed at which [Vdot]O2max was attained interspersed with passive recovery. The work:rest ratio was constant (1:1.5) with trials involving either short (6:9 s) or long (24:36 s) work:rest exercise protocols (total exercise time 8 min). Each trial was followed by a performance run to volitional exhaustion at the same running speed. Testing order was randomized and counterbalanced. Heart rate, oxygen consumption, respiratory exchange ratio, and blood glucose were similar between trials (P > 0.05). Blood lactate concentration was greater during the long than the short exercise protocol (P < 0.05), whereas blood pH was lower during the long than the short exercise protocol (7.28, s = 0.11 and 7.30, s = 0.03 at 20 min, respectively; P < 0.05). Perceptions of effort were greater throughout exercise for the long than the short exercise protocol (16.6, s = 1.4 and 15.1, s = 1.6 at 20 min, respectively; P < 0.05) and correlated with blood lactate (r = 0.43) and bicarbonate concentrations (r = ?0.59; P < 0.05). Although blood lactate concentration at 20 min was related to performance time (r = ?0.56; P < 0.05), no differences were observed between trials for time to exhaustion (short exercise protocol: 95.8 s, s = 30.0; long exercise protocol: 92.0 s, s = 37.1) or physiological responses at exhaustion (P > 0.05). Our results demonstrate that 20 min of intermittent exercise involving a long work:rest duration elicits greater metabolic and perceptual strain than intermittent exercise undertaken with a short work:rest duration but does not affect subsequent run time to exhaustion.  相似文献   

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