Antioxidant-rich beetroot juice does not adversely affect acute neuromuscular adaptation following eccentric exercise

This study examined the effects of beetroot juice on the repeated bout effect (RBE) to eccentric exercise. Twenty-nine recreationally active males performed two bouts of 100-drop jumps, separated by 14–21 days. Using a double-blind, independent groups design, participants consumed either a higher dose beetroot juice (H-BT; 250 ml, n = 10), a lower dose beetroot juice (L-BT; 125 ml, n = 9) or an isocaloric placebo (PLA; 250 ml, n = 10) for 3 days after bout 1; no drinks were consumed after bout 2. Maximal isometric voluntary contraction (MIVC), countermovement jump (CMJ), pressure-pain threshold (PPT) and creatine kinase (CK) were measured pre, post, 24, 48 and 72 h following both bouts. In bout 2, CMJ and MIVC recovered quicker and CK activity was attenuated (versus bout 1) (P < 0.05) in all groups, demonstrating an RBE. At 24 h post bout 1, MIVC was 84.1 ± 16.1, 83.6 ± 11.6, 79.7 ± 15.1% relative to baseline values in the H-BT, L-BT and PLA groups, respectively; at 24 h post bout 2, MIVC recovered to 90.7 ± 13.7, 92.9 ± 6.9, 87.8 ± 6.9, in the H-BT, L-BT and PLA groups, respectively. These findings suggest that supplementation with antioxidant-rich beetroot juice does not adversely affect acute adaptations to a bout of eccentric exercise.     

Effect of stride length manipulation on symptoms of exercise-induced muscle damage and the repeated bout effect

This study assessed the effects of stride length on symptoms of exercise-induced muscle damage after downhill running and whether the extent of the symptoms sustained in a repeated bout of downhill running are influenced by stride length manipulation in the first bout. Eighteen males aged 21.1 - 0.6 years (mean - s) were allocated to one of three groups for bout one: preferred stride frequency, overstride and understride. Bout two was performed 2 weeks later at the participants' preferred stride frequency. Maximal isometric force and perceived muscle soreness were assessed pre-test and 30 min, 24, 48 and 72 h post-exercise for each downhill run. Threefactor analyses of variance with repeated measures on time and bout were used for analysis. Results revealed a three-way interaction for soreness (F 8,60 = 3.56, P ? 0.05) and relative isometric strength (F 5.0,37.8 = 3.2, P ? 0.05). Post-hoc analyses revealed that, after bout one, the overstride group perceived most soreness and the understride group retained most strength. After the second bout, the overstride and preferred stride frequency groups perceived less soreness than the preferred stride frequency group in bout one. Strength retention was greater after bout two for all groups. In conclusion, strength retention after a repeated bout appears to be independent of the damage experienced in the initial bout of downhill running. However, understriding may provide least protection against soreness in a subsequent bout.     

Women show similar central and peripheral fatigue to men after half-marathon*

Women are known to be less fatigable than men in single-joint exercises, but fatigue induced by running has not been well understood. Here we investigated sex differences in central and peripheral fatigue and in rate of force development (RFD) in the knee extensors after a half-marathon run. Ten male and eight female amateur runners (aged 25–50 years) were evaluated before and immediately after a half-marathon race. Knee extensors forces were obtained under voluntary and electrically evoked isometric contractions. Maximal voluntary isometric contraction (MVC) force and peak RFD were recorded. Electrically doublet stimuli were delivered during the MVC and at rest to calculate the level of voluntary activation and the resting doublet twitch. After the race, decreases in MVC force (males: ?11%, effect size [ES] 0.52; females: ?11% ES 0.33), voluntary activation (males: ?6%, ES 0.87; females: ?4%, ES 0.72), and resting doublet twitch (males: ?6%, ES 0.34; females: ?8%, ES 0.30) were found to be similar between males and females. The decrease in peak RFD was found to be similar between males and females (males: ?14%, ES 0.43; females: ?15%, ES 0.14). Half-marathon run induced both central and peripheral fatigue, without any difference between men and women. The maximal and explosive strength loss was found similar between sexes. Together, these findings do not support the need of sex-specific training interventions to increase the tolerance to neuromuscular fatigue in half-marathoners.     

Effect of stride length manipulation on symptoms of exercise-induced muscle damage and the repeated bout effect

This study assessed the effects of stride length on symptoms of exercise-induced muscle damage after downhill running and whether the extent of the symptoms sustained in a repeated bout of downhill running are influenced by stride length manipulation in the first bout. Eighteen males aged 21.1 +/- 0.6 years (mean +/- s) were allocated to one of three groups for bout one: preferred stride frequency, overstride and understride. Bout two was performed 2 weeks later at the participants' preferred stride frequency. Maximal isometric force and perceived muscle soreness were assessed pre-test and 30 min, 24, 48 and 72 h post-exercise for each downhill run. Three-factor analyses of variance with repeated measures on time and bout were used for analysis. Results revealed a three-way interaction for soreness (F8,60 = 3.56, P < 0.05) and relative isometric strength (F5.0,37.8 = 3.2, P < 0.05). Post-hoc analyses revealed that, after bout one, the overstride group perceived most soreness and the understride group retained most strength. After the second bout, the overstride and preferred stride frequency groups perceived less soreness than the preferred stride frequency group in bout one. Strength retention was greater after bout two for all groups. In conclusion, strength retention after a repeated bout appears to be independent of the damage experienced in the initial bout of downhill running. However, understriding may provide least protection against soreness in a subsequent bout.     

Variability in muscle damage after eccentric exercise and the repeated bout effect

The first purpose of this study was to determine a possible explanation for the variability in the response to eccentric exercise by having participants repeat the same exercise 1 year apart. The second purpose was to examine whether initial injury in response to eccentric exercise was associated with the extent of the repeated bout effect (RBE). Male students performed 30 eccentric contractions (ECC) of the elbow flexors using a dumbbell set at 80% of the pre-exercise maximal isometric force (MIF). Participants were then classified into low (LR; n=6), medium (MR; n=6), high (HR; n=5), and higher (HrR; n=7) based on the increase in blood creatine kinase (CK) activity. A year later, participants repeated this exercise (ECC30). Four days after ECC30, participants performed 70 eccentric contractions (ECC70). Range of motion, MFI upper arm circumference, soreness, and blood CK activity were measured before and up to 9 days after each bout. The change in the criterion measures following ECC and ECC30 were similar for each group. There were no further changes in all parameters after ECC70 for MR, HR, and HrR, although there was a small increase in CK after ECC70 for LR. LR showed a smaller RBE after ECC70 compared with the other groups. It is concluded that participants who exercised 1 year apart showed remarkably similar responses between the bouts. The extent of the RBE following the second bout for the LR group is less for participants who demonstrate the least evidence of muscle damage after a first exercise bout.     

Neuromuscular variables affecting the magnitude of force loss after eccentric exercise

The aim of this study was to examine neuromuscular variables contributing to differences in force loss after participants were exposed to the same relative bout of eccentric exercise. Thirty-six males performed 50 maximal eccentric contractions of the elbow flexors and were stratified into high responders (n = 10) and low responders (n = 10) based on force loss 36 h after exercise. Maximal voluntary isometric contractions (MVCs) and electromyography (EMG) were measured at baseline and 36 h after exercise. During eccentric exercise, mean peak torque, mean end-range torque from the final 25% of each trial and total angular impulse were computed over 25 contractions in each of two bouts. The slope of the change in these values for each 25 eccentric contractions was calculated for each participant using linear regression. At baseline, MVC was not different between groups (low responders: 97.0 +/- 9.6 N x m; high responders: 82.7 +/- 6.4 N x m; P = 0.08). High responders demonstrated a 68% (range 62-78%) reduction in MVC and low responders a 39% (29-48%) reduction after exercise. Peak torque, end-range torque and total angular impulse were 13%, 40% and 33% higher, respectively, in the low than in the high responders (peak torque: P = 0.0002; end-range torque: P < 0.0001; total angular impulse: P < 0.001). The rate of decline in peak torque slope was greater in high than in low responders (P = 0.044). In conclusion, lower peak torque, end-range torque and total angular impulse during eccentric contractions and a greater peak torque slope may identify high responders to eccentric exercise.     

Indirect evidence of human skeletal muscle damage and collagen breakdown after eccentric muscle actions.

Indirect markers of muscle damage and collagen breakdown were recorded for up to 9 days after a bout of concentric, followed by a bout of eccentric, muscle actions. Nine untrained participants performed two bouts of 50 maximum effort repetitions on an isokinetic dynamometer (angular velocity 1.05 rad x s(-1), range of motion 1.75 rad). An initial concentric bout of muscle actions was followed by an eccentric bout 21 days later, using the same knee extensors. Concentric actions induced no changes in maximum voluntary isometric contraction force (MVC), nor induced any changes in the serum enzyme activities of creatine kinase, a lactate dehydrogenase isoenzyme (LDH-1), or alkaline phosphatase. Similarly, concentric actions induced no change in markers of collagen breakdown, namely plasma hydroxyproline and serum type 1 collagen concentration. In contrast, eccentric actions induced a 23.5+/-19.0% (mean+/-s) decrease in MVC immediately post-exercise (P < 0.05), and increased the serum enzyme activities of creatine kinase and LDH-1 to 486+/-792 and 90+/-11 IU.l(-1) respectively on day 3 post-exercise, and to 189+/-159 and 96+/-13 IU x l(-1) respectively on day 7 post-exercise (all P< 0.05). Eccentric actions induced no significant changes in plasma hydroxyproline, but increased collagen concentration on days 1 and 9 post-exercise (48.6% and 44.3% increases above pre-exercise on days 1 and 9 respectively; both P < 0.05). We conclude that eccentric but not concentric actions may result in temporary muscle damage, and that collagen breakdown may also be affected by eccentric actions. With caution, indices of collagen breakdown may be used to identify exercise-induced damage to connective tissue.     

Variability in Muscle Damage After Eccentric Exercise and the Repeated Bout Effect

The first purpose of this study was to determine a possible explanation for the variability in the response to eccentric exercise by having participants repeat the same exercise 1 year apart. The second purpose was to examine whether initial injury in response to eccentric exercise was associated with the extent of the repeated bout effect (RBE). Male students performed 30 eccentric contractions (ECC) of the elbow flexors using a dumbbell set at 80% of the pre-exercise maximal isometric force (MIF). Participants were then classified into low (LR; n = 6), medium (MR; n = 6), high (HR; n = 5), and higher (HrR; n = 7) based on the increase in blood creatine kinase (CK) activity. A year later, participants repeated this exercise (ECC30). Four days after ECC30, participants performed 70 eccentric contractions (ECC70). Range of motion, MIF, upper arm circumference, soreness, and blood CK activity were measured before and up to 9 days after each bout. The change in the criterion measures following ECC and ECC30 were similar for each group. There were no further changes in all parameters after ECC70 for MR, HR, and HrR, although there was a small increase in CK after ECC70 for LR. LR showed a smaller RBE after ECC70 compared with the other groups. It is concluded that participants who exercised 1 year apart showed remarkably similar responses between the bouts. The extent of the RBE following the second bout for the LR group is less for participants who demonstrate the least evidence of muscle damage after a first exercise bout.     

Energy cost and kinematics of level,uphill and downhill running: fatigue-induced changes after a mountain ultramarathon

This study aimed to determine whether the fatigue induced by a mountain ultramarathon (MUM) led to changes in energy cost and kinematic during level and graded running. Pre- and post-race, 14 ultratrail runners ran on a level, uphill (5%) and downhill (5%) treadmill at 10 km · h^?1. Kinematic data were acquired using a photocell system. Post-race, the downhill energy cost increased by 13.1% (P < 0.001). No change was noted in level and uphill running. Duty factor and stride frequency were increased, whereas swing time, cycle time and stride length were decreased in all conditions (P < 0.05). Contact time was increased and the rate of force generation was decreased only in the uphill and downhill conditions (P < 0.05). Positive correlations were observed between performance time and the pre- to post-changes in the energy cost of level (r = 0.52, P = 0.04) and uphill running (r = 0.50, P = 0.04). MUM-induced fatigue resulted in physiological and spatiotemporal changes, though the response to fatigue varied considerably between running conditions. These changes resulted in a significant increment only in the downhill energy cost. Incorporating downhill locomotion in the training programmes of ultratrailers may help to improve performance-related physiological and biomechanical parameters.     

Rate of Force Development in the Handgripping Muscles by Females as a Function of Fatigue Level

Abstract

Twenty-eight young, adult women were tested for maximum voluntary contraction (MVC) of the grip flexors and were then given five fatigue trials in which the task was to maintain a maximum isometric contraction until the strength level had been degraded to either 80%, 60%, or 40% MVC. At that time, the subject relaxed and within one second was commanded to generate a single contraction as rapidly and forcefully as possible. Testing was also conducted in the nonfatigued state (1.00 MVC). Forces were determined at 4, 8, 16, 32, 64, 128, 256, 512, and 1,024 msec following the initial deflection of the pen from the baseline. Normalized force values were calculated by dividing the force expressed at the various time intervals by the maximum force generated under that condition at 1,024 msec. For both absolute and normalized rate of force development, the highest rate was attained between 32–64 msec. During that time period, the rate of absolute force development was reduced 10% at the 80% MVC level, 30% at 60% MVC, and 53% at 40% MVC. There was a definite pattern of depressed rate of absolute force development up to 256 msec at the higher fatigue levels. For normalized force, fatiguing a muscle to 80% MVC had no effect except at 64 msec where a greater percentage of maximal force was attained than at 1.00 MVC. Beyond that level of fatigue, however, normalized force tended to be adversely affected as fatigue progressed. The time required to develop either 50% or 70% of maximal force was significantly longer for the 40% MVC level than for the remaining conditions. In addition, the time necessary to develop 70% of maximal force was longer for the 60% MVC fatigue level than for the 80% MVC level.     

Metabolic cost of level,uphill, and downhill running in highly cushioned shoes with carbon-fiber plates

BackgroundCompared to conventional racing shoes, Nike Vaporfly 4% running shoes reduce the metabolic cost of level treadmill running by 4%. The reduction is attributed to their lightweight, highly compliant, and resilient midsole foam and a midsole-embedded curved carbon-fiber plate. We investigated whether these shoes also could reduce the metabolic cost of moderate uphill (+3°) and downhill (–3°) grades. We tested the null hypothesis that, compared to conventional racing shoes, highly cushioned shoes with carbon-fiber plates would impart the same ～4% metabolic power (W/kg) savings during uphill and downhill running as they do during level running.MethodsAfter familiarization, 16 competitive male runners performed six 5-min trials (2 shoes × 3 grades) in 2 Nike marathon racing-shoe models (Streak 6 and Vaporfly 4%) on a level, uphill (+3°), and downhill (–3°) treadmill at 13 km/h (3.61 m/s). We measured submaximal oxygen uptake and carbon dioxide production during Minutes 4–5 and calculated metabolic power (W/kg) for each shoe model and grade combination.ResultsCompared to the conventional shoes (Streak 6), the metabolic power in the Vaporfly 4% shoes was 3.83% (level), 2.82% (uphill), and 2.70% (downhill) less (all p < 0.001). The percent of change in metabolic power for uphill running was less compared to level running (p = 0.04; effect size (ES) = 0.561) but was not statistically different between downhill and level running (p = 0.17; ES = 0.356).ConclusionOn a running course with uphill and downhill sections, the metabolic savings and hence performance enhancement provided by Vaporfly 4% shoes would likely be slightly less overall, compared to the savings on a perfectly level race course.     

Do aerobic characteristics explain isometric exercise-induced neuromuscular fatigue and recovery in upper and lower limbs?

This study investigated the relationships between aerobic characteristics and (i) neuromuscular fatigue induced by 2-min sustained isometric maximal voluntary contractions (MVC) and (ii) subsequent recovery, in the upper and lower limbs. In a pseudo-randomized order, eleven healthy males completed four sessions on different days: maximal incremental cycling test (100 W + 40 W every 2 min); maximal arm-cranking test (50 W + 20 W every 2 min); and 2-min sustained isometric MVCs of the knee extensors (KE) and elbow flexors (EF). Neuromuscular assessment was performed with transcranial magnetic and peripheral nerve stimulation to evaluate central and peripheral neuromuscular factors of fatigue and the subsequent recovery. Peak oxygen uptake, gas exchange threshold and the corresponding power outputs were correlated with recovery of voluntary force after the 2-min KE MVC. Regression analysis showed that power output at the gas exchange threshold alone explained 72% of the variability in ?recovery of KE voluntary force. No relationships with fatigue or recovery in EF were observed. These results suggest that participants with greater aerobic capacities experience the same amount of fatigue and faster recovery of voluntary force in KE but not EF. The potential reasons behind the relationship in KE but not EF are discussed.     

Neuromuscular variables affecting the magnitude of force loss after eccentric exercise

The aim of this study was to examine neuromuscular variables contributing to differences in force loss after participants were exposed to the same relative bout of eccentric exercise. Thirty-six males performed 50 maximal eccentric contractions of the elbow flexors and were stratified into high responders (n?=?10) and low responders (n?=?10) based on force loss 36 h after exercise. Maximal voluntary isometric contractions (MVCs) and electromyography (EMG) were measured at baseline and 36 h after exercise. During eccentric exercise, mean peak torque, mean end-range torque from the final 25% of each trial and total angular impulse were computed over 25 contractions in each of two bouts. The slope of the change in these values for each 25 eccentric contractions was calculated for each participant using linear regression. At baseline, MVC was not different between groups (low responders: 97.0?±?9.6 N?·?m; high responders: 82.7?±?6.4 N?·?m; P?=?0.08). High responders demonstrated a 68% (range 62-78%) reduction in MVC and low responders a 39% (29-48%) reduction after exercise. Peak torque, end-range torque and total angular impulse were 13%, 40% and 33% higher, respectively, in the low than in the high responders (peak torque: P?=?0.0002; end-range torque: P?<?0.0001; total angular impulse: P?<?0.001). The rate of decline in peak torque slope was greater in high than in low responders (P?=?0.044). In conclusion, lower peak torque, end-range torque and total angular impulse during eccentric contractions and a greater peak torque slope may identify high responders to eccentric exercise.     

Knee extension fatigue attenuates repeated force production of the elbow flexors

Abstract

Non-local muscle fatigue has been demonstrated with unilateral activities, where fatiguing one limb alters opposite limb forces. Fewer studies have examined if non-local fatigue occurs with unrelated muscles. The purpose of this study was to investigate if knee extensors fatigue alters elbow flexors force and electromyography (EMG) activity. Eighteen males completed a control and fatiguing session (randomised). Blood lactate was initially sampled followed by three maximal voluntary contractions (MVC) with the elbow flexors and two with the knee extensors. Thereafter, subjects either sat (control) or performed five sets of bilateral dynamic knee extensions to exhaustion using a load equal to the dominant limb MVC (1-min rest between sets). Immediately afterwards, subjects were assessed for blood lactate and unilateral knee extensors MVC, and after 1 min performed a single unilateral elbow flexor MVC. Two minutes later, subjects performed 12 unilateral elbow flexor MVCs (5 s contraction/10 s rest) followed by a third blood lactate test. Compared to control, knee extensor force dropped by 35% (p < 0.001; ES = 1.6) and blood lactate increased by 18% (p < 0.001; ES = 2.8). Elbow flexor forces were lower after the fatiguing protocol only during the last five MVCs (p < 0.05; ES = ～0.58; ～5%). No changes occurred between conditions in EMG. Elbow flexor forces significantly decreased after knee extensors fatigue. The effect was revealed during the later stages of the repeated MVCs protocol, demonstrating that non-local fatigue may have a stronger effect on repeated rather than on single attempts of maximal force production.     

Running economy and effort after cycling: Effect of methodological choices

ABSTRACT

Prior exercise can negatively affect movement economy of a subsequent task. However, the impact of cycling exercise on the energy cost of subsequent running is difficult to ascertain, possibly because of the use of different methods of calculating economy. We examined the influence of a simulated cycling bout on running physiological cost (running economy, heart rate and ventilation rates) and perceptual responses (ratings of perceived exertion and effort) by comparing two running bouts, performed before and after cycling using different running economy calculation methods. Seventeen competitive male triathletes ran at race pace before and after a simulated Olympic-distance cycling bout. Running economy was calculated as V?O₂ (mL?kg^?1?min^?1), oxygen cost (EO₂, mL?kg^?1?m^?1) and aerobic energy cost (E_aer, J?kg^?1?m^?1). All measures of running economy and perceptual responses indicated significant alterations imposed by prior cycling. Despite a good level of agreement with minimal bias between calculation methods, differences (p < 0.05) were observed between E_aer and both V?O₂ and EO₂. The results confirmed that prior cycling increased physiological cost and perceptual responses in a subsequent running bout. It is recommended that E_aer be calculated as a more valid measure of running economy alongside perceptual responses to assist in the identification of individual responses in running economy following cycling.     

The effects of fast bowling fatigue and adhesive taping on shoulder joint position sense in amateur cricket players in Victoria,Australia

The impact that muscle fatigue and taping have on proprioception in an applied sporting context remains unclear. The purpose of this study was to investigate disturbances in position sense at the shoulder joint, and asses the effectiveness of adhesive tape in preventing injury and improving performance, after a bout of cricket fast bowling. Among amateur cricket players (N = 14), shoulder position sense, maximum voluntary contraction (MVC) force and bowling accuracy was assessed before and immediately after a fatiguing exercise bout of fast bowling. Participants were tested with the shoulder taped and untapped. Shoulder extension MVC force dropped immediately and 30 min after the exercise (P < 0.05 and P < 0.05, respectively). Position sense errors increased immediately after exercise (P < 0.05), shifting in the direction of shoulder extension for all measurements. Taping had no effect on position errors before exercise, but did significantly reduce position errors after exercise at mid-range shoulder flexion angles (45° and 60°; P < 0.05 and P < 0.05, respectively). Taping had no significant effect on bowling accuracy. These findings may be explained by a body map shift towards a gravity neutral position. Added cutaneous input from the tape is proposed to contribute more to shoulder position sense when muscles are fatigued.     

反复离心运动对大鼠骨骼肌损伤和蛋白质降解机制的影响

目的:探讨连续离心运动训练对骨骼肌中Calpain和Ubiquitin含量的影响及其与骨骼肌损伤之间的关系;方法:雄性SD大鼠29只随机分为对照组、离心训练后即刻组、24 h组和7天组.训练组大鼠连续进行7天的下坡跑运动,分别在末次训练后即刻,24 h和第7天取股四头肌,测定股四头肌的超微结构、血清LDH和CK活性以及骨骼肌中Calpaim-1、Calpain-2和Ubiquitin含量;结果:1)7天离心训练后即刻和24h,股四头肌超微结构的损伤性变化呈渐进性加重,离心训练后24 h组出现明显的肌丝坏死.训练后第7天仍不能完全恢复.血清CK和LDH活性的变化与大鼠股四头肌超微结构的变化相一致.2)与对照组相比,末次训练后即刻骨骼肌中Calpain-1、Calpain-2和Ubiquitin含量均显著升高;训练后24 h,Calpain-1和Calpanin-2含量进一步升高,其中,Calpain-1显著高于对照组和训练后24 h组,Calpain-2虽显著高于对照组,但与训练后即刻组相比无显著性差异;而Ubiquitin含量显著低于训练后即刻组.训练后第7天,Calpain-1和Calpain-2含量显著低于训练后24 h组,但仍然高于对照组;而Ubiquitin含量虽高于训练后24 h组和对照组,但无显著性差异;结论:1)连续的离心运动可能对骨骼肌纤维的损伤产生一定的累加作用;2)短期连续的离心训练后,骨骼肌中Calpain和Ubiquitin的动态变化几乎与骨骼肌超微结构的动态变化相一致.离心运动训练导致骨骼肌中Calpain和Ubiquitin含量的增加,可能是导致骨骼肌累积性损伤的重要机制.     

Indirect evidence of human skeletal muscle damage and collagen breakdown after eccentric muscle actions

Indirect markers of muscle damage and collagen breakdown were recorded for up to 9 days after a bout of concentric, followed by a bout of eccentric, muscle actions. Nine untrained participants performed two bouts of 50 maximum effort repetitions on an isokinetic dynamometer (angular velocity 1.05 rad.s-1, range of motion 1.75 rad). An initial concentric bout of muscle actions was followed by an eccentric bout 21 days later, using the same knee extensors. Concentric actions induced no changes in maximum voluntary isometric contraction force (MVC),nor induced any changes in the serum enzyme activities of creatine kinase, a lactate dehydrogenase isoenzyme (LDH-1), or alkaline phosphatase. Similarly, concentric actions induced no change in markers of collagen breakdown,namely plasma hydroxyproline and serum type 1 collagen concentration.In contrast,eccentric actions induced a 23.5 ± 19.0% (mean ± s) decrease in MVC immediately post-exercise (P< 0.05), and increased the serum enzyme activities of creatine kinase and LDH-1 to 486 ± 792 and 90 ± 11 IU.l-1 respectively on day 3 post-exercise, and to 189 ± 159 and 96 ±13 IU.l-1 respectively on day 7 post-exercise (all P < 0.05). Eccentric actions induced no significant changes in plasma hydroxyproline, but increased collagen concentration on days 1 and 9 post-exercise (48.6% and 44.3% increases above pre-exercise on days 1 and 9 respectively; both P < 0.05). We conclude that eccentric but not concentric actions may result in temporary muscle damage, and that collagen breakdown may also be affected by eccentric actions. With caution, indices of collagen breakdown may be used to identify exercise-induced damage to connective tissue.     

The effects of carbohydrate supplementation during repeated bouts of prolonged exercise on saliva flow rate and immunoglobulin A

The purpose of this study was to assess the effect of carbohydrate (CHO) feeding during different periods of two 90-min cycling bouts (the first bout began at 09:00?h and the second bout began at 13:30?h) at 60% maximal oxygen uptake ([Vdot]O_2max) on saliva flow rate and saliva immunoglobulin A (sIgA) responses to the second exercise bout. The study consisted of three investigations: carbohydrate supplementation during (1) the first hour of the recovery interval (CHO-REC), (2) during the first bout of exercise and (3) during the second bout of exercise. Each investigation included two trials completed in a counterbalanced order and separated by at least 4 days. Participants consumed a lemon-flavoured 10% w/v carbohydrate beverage or placebo (22?ml?·?kg^?1 body mass) in the first hour of the recovery interval (n = 8) and 500?ml just before exercise, followed by 250?ml every 20?min during exercise in the first (n = 9) and second exercise bouts (n = 9). Timed unstimulated saliva samples were collected at 10?min before exercise, after 48?–?50?min of exercise and during the last 2?min of exercise, at 1?h post exercise, 2?h post exercise (first exercise bout only), and 18?h post exercise (second exercise bout only). Venous blood samples were taken 5?min before exercise and immediately after exercise for both exercise bouts in all trials. The main findings of the present study were as follows. First, carbohydrate ingestion during both exercise bouts, but not during the recovery interval, better maintained plasma glucose concentrations and attenuated the increase in plasma adrenaline and cortisol concentrations after the second exercise bout compared with placebo. Second, carbohydrate feeding had no effect on saliva flow rate and sIgA secretion rate compared with placebo. Third, saliva flow rate and sIgA concentration returned to pre-exercise bout 1 values within 2?h in all trials. Fourth, there was no delayed effect of exercise on oral immunity. These findings suggest that carbohydrate ingestion during the first or second bout of exercise, but not during the recovery interval, is likely to better maintain plasma glucose concentrations and attenuate the responses of plasma stress hormones to a second exercise bout than ingestion of fluid alone. Two bouts of 90?min cycling at 60% [Vdot]O_2max on the same day appears to inhibit saliva flow rate during the second exercise bout but does not alter sIgA transcytosis. Our results show that carbohydrate ingestion during any period of two prolonged exercise bouts does not induce different effects on oral immunity compared with placebo.     

The effects of carbohydrate supplementation during repeated bouts of prolonged exercise on saliva flow rate and immunoglobulin A

The purpose of this study was to assess the effect of carbohydrate (CHO) feeding during different periods of two 90-min cycling bouts (the first bout began at 09:00?h and the second bout began at 13:30 h) at 60% maximal oxygen uptake(VO2max) on saliva flow rate and saliva immunoglobulin A (sIgA) responses to the second exercise bout. The study consisted of three investigations: carbohydrate supplementation during (1) the first hour of the recovery interval (CHO-REC), (2) during the first bout of exercise and (3) during the second bout of exercise. Each investigation included two trials completed in a counterbalanced order and separated by at least 4 days. Participants consumed a lemon-flavoured 10% w/v carbohydrate beverage or placebo (22 ml.kg-1 body mass) in the first hour of the recovery interval (n=8) and 500 ml just before exercise, followed by 250 ml every 20 min during exercise in the first (n=9) and second exercise bouts (n=9). Timed unstimulated saliva samples were collected at 10 min before exercise, after 48-50 min of exercise and during the last 2 min of exercise, at 1 h post exercise, 2 h post exercise (first exercise bout only), and 18 h post exercise (second exercise bout only). Venous blood samples were taken 5 min before exercise and immediately after exercise for both exercise bouts in all trials. The main findings of the present study were as follows. First, carbohydrate ingestion during both exercise bouts, but not during the recovery interval, better maintained plasma glucose concentrations and attenuated the increase in plasma adrenaline and cortisol concentrations after the second exercise bout compared with placebo. Second, carbohydrate feeding had no effect on saliva flow rate and sIgA secretion rate compared with placebo. Third, saliva flow rate and sIgA concentration returned to pre-exercise bout 1 values within 2 h in all trials. Fourth, there was no delayed effect of exercise on oral immunity. These findings suggest that carbohydrate ingestion during the first or second bout of exercise, but not during the recovery interval, is likely to better maintain plasma glucose concentrations and attenuate the responses of plasma stress hormones to a second exercise bout than ingestion of fluid alone. Two bouts of 90 min cycling at 60% VO2max on the same day appears to inhibit saliva flow rate during the second exercise bout but does not alter sIgA transcytosis. Our results show that carbohydrate ingestion during any period of two prolonged exercise bouts does not induce different effects on oral immunity compared with placebo.