Repeated Bouts Research Articles

Metabolic And Hemodynamic Responses To High Intensity Interval Training With Various Recovery Intervals

For more than twenty years, the Tabata protocol has provided the basis for high intensity interval training (HIIT). Although the improvements associated with the protocol are laudable, an intensity of 170% of max VO2, is difficult for even highly motivated athletes to achieve. A repeated bout HIIT protocol at 100% of Max VO2 may be a more tolerable option, if it achieves a similar metabolic stress. PURPOSE: The purpose was to determine the metabolic cost of 8 repetitions of HIIT at a workload equivalent to 100% Max VO2 (HIIT) for 20 sec with recovery intervals of 10, 20, 30 and 40 sec at 20% of Max VO2. METHODS: 14 recreationally active college-age students (age: 21.6±1.1 yrs., height: 171.410.5 cm, body mass: 75.0±10.6 kg, max VO2 2.89±.67, 8 ♂) volunteered to participate in a randomized, single-blind crossover design study with a minimum of 4 days between trials. A max VO2 ramp protocol on a Lode Cycle ergometer preceded the HIIT trials and established the max workload. VO2 was obtained by continuous open circuit spirometry and blood lactate by finger puncture. Excess Post Exercise O2 Consumption (EPOC) was obtained for 20 min. RESULTS: Statistical analysis by ANOVA with repeated measures (P<.05) was applied to the following data.CONCLUSION: The prescribed HIIT work intervals provide ample metabolic stimulus, however recovery intervals in excess of 30 seconds substantially attenuate the oxygen uptake, while still requiring a strong anaerobic contribution. The use of eight repeat bouts of HIIT at a workload equivalent to 100% of max VO2 may be a viable alternative to the traditional Tabata protocol.

A Nonadapted Cardiac Autonomic Regulation Following Repeated Bouts Of Eccentric Exercise

A Nonadapted Cardiac Autonomic Regulation Following Repeated Bouts Of Eccentric Exercise

The Effect Of Percussive Massage Versus Foam Rolling On Recovery Between Two 91 Meter Swims

Swim competition often requires repeat bouts of the same event, as well as several different events for each swimmer. Multiple events during the competition may influence subsequent outcomes, thus various strategies are employed to enhance recovery and reduce fatigue. The search for the optimal recovery is never ending. Two of the more popular recovery techniques include foam rolling massage and percussive massage. There is a paucity of research to support the efficacy of either. PURPOSE: The purpose of this study was to assess the effect of no massage (NM), foam roller massage (FM) and percussive massage (PM) on repeated swim performance separated by 30 minutes of recovery. METHODS: 8 male and 12 female college-aged swimmers (age: 20.9 ± 2.8 yr., height: 171.7 ± 8.6 cm., weight 70.3 ± 10.9 kg.) volunteered to participate in three 91 meter repeat swim trials. Blood lactate (BL) was measured two minutes pre-swim and three minutes post-swim. A randomized, single blind cross-over application of FM, PM, or NM was conducted between each of the two 91meter maximal velocity swims. For both FM and PM the treatment was applied bilaterally for a total of 16 minutes with 2 minutes per muscle group (calves, hamstring, quadriceps, and upper arms). RESULTS: For the first vs second bout of each trial, male times were 52.3 ± 2.5 vs 52.7 ± 2.7 sec, 52.2 ± 2.7 vs 52.3 ± 2.8 sec, and 52.5 ± 2.3 vs 52.4 ± 2.6 sec and female times were 63.7 ± 3.6 vs 63.9 ± 3.8 sec, 63.4 ± 3.9 vs 63.8 ± 3.8 sec and 63.9 ± 4.0 vs 63.0 ± 3.8 sec for FM, PM, and NM trials, respectively. Statistical analysis by dependent T-test (P<.05) revealed NSD (p>.05) pre vs post between trials, except that the second swim was slower than the first swim in the male FM trials. Mean BL values post first swim were 8.5 ± 3 mmol, 8.8 ± 2.56 mmol, 9.1 ± 2.2 mmol, and pre second swim lactate values were 3.4 ± 1.8 mmol, 3.9 ± 1.6 mmol, 4.0 ± 1.7 mmol for FM, PM, and NM respectively. Statistical analysis of BL by ANOVA revealed no significant difference across all trials (p>.05). CONCLUSION: The mode of recovery did not improve velocity in repeat 91 meter swim bouts or alter the time course for post-swim BL recovery. Supported, in part by a grant from Theragun®.

Verification Bout Criteria In The Heat: A Training Status Comparison

The use of verification bouts (VRF) to confirm maximal oxygen consumption (V̇O2max) in thermoneutral conditions is well established. Less is known about the utility of VRF in the heat. The impact of a hot environment may affect trained and untrained subjects differently. Data demonstrating the impact of heat on repeat bouts of high-intensity exercise may be useful for individuals performing an unaccustomed activity in the heat. PURPOSE: To compare V̇O2, heart rate (HR), and rating of perceived exertion (RPE) from a graded exercise test (GXT) vs. VRF in trained vs. untrained subjects. METHODS: Aerobically trained (T) (n=10) and untrained (UT) (n=11) college-aged males volunteered. Baseline gastrointestinal temperature (Tgi) and resting V̇O2, RPE, and HR values were collected then subjects rested in a heated chamber (39°C, 31% relative humidity) for 20 min before completing the GXT. Post-GXT, subjects exited the chamber and rested in a thermoneutral room (22°C, 40%RH) until Tgi returned to baseline. Subjects re-entered chamber and repeated pre-GXT procedures prior to VRF. For VRF, subjects warmed-up cycled at 60% maximal wattage (Wmax) from GXT and then cycled at 110% Wmax until exhaustion. V̇O2, HR, and RPE values from the last complete min were used for comparison. A 2 × 2 [(T vs. UT)×(GXT vs. VRF)] mixed-factor ANOVA with Bonferroni post hoc tests and an alpha of 0.05 was used for analysis. RESULTS: V̇O2: trained cyclists V̇O2max was greater than untrained (56.4±8.6 vs. 40.1±5.9 mL·kg-1·min-1, p<0.001); V̇O2 during GXT was greater than VRF for both groups (p=0.013, ηp2=0.29). HR: subjects had significantly higher HR during GXT vs. VRF (T:188vs.178bpm; UT:189vs.181bpm; p<0.001, ηp2=0.74) and HR was not significantly different between groups (p=0.77). RPE: There was a significant trial×training interaction (p=0.04, ηp2=0.21), and a significant main effect for training status with trained cyclists expressing higher RPE than untrained in GXT & VRF(19vs.18; 19vs.17;p=0.002). CONCLUSION: The results indicated that RPE may be tied to V̇O2 more than HR in the heat in trained subjects. V̇O2 during VRF in the heat was less than V̇O2max in all subjects during GXT which may confirm V̇O2max or indicate premature fatigue due to heat. Thus, a VRF may not be necessary for the determination of V̇O2max in the heat for untrained subjects.

The Oxidative Contribution Of Eight Repeat Bouts Of High Intensity Interval Training

The oxidative contribution to eight repeat bouts of high intensity interval training John Petrizzo, Michele Aquino, Colin Shaw, Justin St Peter, Erica Koutch, Rebecca Flax, Kerianne Nordland, John Wygand, FACSM, Robert Otto, FACSM, Adelphi University, Garden City, NY 11530. Email: [email protected] Interval training requires bouts of work followed by recovery intervals. The intensity of the work interval impacts the metabolic response of the recovery interval. PURPOSE: The purpose was to determine the oxidative cost of both the work (W) interval and the recovery (R) interval during 8 continuous repetitions of high intensity interval training (HIIT) at a workload equivalent to 100% Max VO2. METHODS: All 20 second work intervals were followed by recovery intervals of 10, 20, 30 and 40 sec at 20% of Max VO2. 14 recreationally active college-age students (age: 21.6±1.1 yrs., height: 171.41±0.5 cm, body mass: 75.0±10.6 kg, max VO2 2.89±.67, 8 ♂) volunteered to participate in a randomized, single-blind crossover design study with a minimum of 4 days between trials. A max VO2 ramp protocol on a Lode Cycle ergometer preceded the HIIT trials and established the max workload. VO2 was obtained by continuous open circuit spirometry. RESULTS: Statistical analysis by ANOVA with repeated measures (∗P<.05) was applied to these data.CONCLUSION: Short recovery intervals of 30 seconds or less provide the greatest oxidative stress during interval training, which may be attributed to insufficient phosphagen resynthesis during recovery.

Effect of autonomic nerve activation in different ratio of heart rate/breathing rate during repeated bouts of cycling exercise

Effect of autonomic nerve activation in different ratio of heart rate/breathing rate during repeated bouts of cycling exercise

Effect of Tapping Bout Duration During Freely Chosen and Passive Finger Tapping on Rate Enhancement

The present study investigated whether the duration of the first tapping bout, which could also be considered ‘the priming’, would play a role for the occurrence of the behavioral phenomenon termed repeated bout rate enhancement. Eighty-eight healthy individuals were recruited. Sixty-three of these demonstrated repeated bout rate enhancement and they were assigned to two different groups, which performed either active or passive tapping as priming. The durations of the first tapping bouts, which acted as priming, were 20, 60, 120, and 180 s. Following the first bout there was a 10 min rest and a subsequent 180 s tapping bout performed at freely chosen tapping rate. Vertical displacement and tapping force data were recorded. Rate enhancement was elicited independently of the duration of the first bout in both groups. Rate enhancement occurred without concurrent changes of the magnitude of vertical displacement, time to peak force, and duration of finger contact phase. The peak force was reduced when 180 s of tapping had been performed as priming. The increased tapping rate following priming by as little as 20 s active or passive tapping, as observed here, is suggested to be a result of increased net excitability of the nervous system.

The Effect of Orally Dosed Levagen+™ (palmitoylethanolamide) on Exercise Recovery in Healthy Males-A Double-Blind, Randomized, Placebo-Controlled Study.

The aim of this study was to evaluate the effect of palmitoylethanolamide (PEA), a cannabimimetic compound and lipid messenger, on recovery from muscle damaging exercise. Twenty-eight healthy young male participants attended the laboratory four times on subsequent days. In the first visit, baseline characteristics were recorded before participants were randomized to consume either liquid PEA (167.5 mg Levagen+ with 832.5 mg maltodextrin) or a matched placebo (1 g maltodextrin) drink. Leg press exercise consisted of four sets at 80% of one repetition maximum followed by a performance set. Muscle soreness, thigh circumference, blood lactate concentration, biomarkers of muscle damage and inflammation, and transcription factor pathways were measured pre- and immediately post-exercise and again at 1, 2, 3, 24, 48, and 72 h post-exercise. The leg press exercise increased (p < 0.05) blood lactate concentration and induced muscle damage as evidenced by increased muscle soreness, thigh circumference, biomarkers of muscle damage, and concentrations of tumor necrosis factor-α. PEA reduced (p < 0.05) myoglobin and blood lactate concentrations and increased protein kinase B phosphorylation following exercise. Taken together, these results indicate PEA supplementation may aid in muscle recovery from repeat bouts of exercise performed within a short duration by reducing myoglobin and lactate concentration.

Acute high-intensity and moderate-intensity interval exercise do not change corticospinal excitability in low fit, young adults.

Previous research has demonstrated a lack of neuroplasticity induced by acute exercise in low fit individuals, but the influence of exercise intensity is unclear. In the present study, we assessed the effect of acute high-intensity (HI) or moderate-intensity (MOD) interval exercise on neuroplasticity in individuals with low fitness, as determined by a peak oxygen uptake (VO2peak) test (n = 19). Transcranial magnetic stimulation (TMS) was used to assess corticospinal excitability via area under the motor evoked potential (MEP) recruitment curve before and following training. Corticospinal excitability was unchanged after HI and MOD, suggesting no effect of acute exercise on neuroplasticity as measured via TMS in sedentary, young individuals. Repeated bouts of exercise, i.e., physical training, may be required to induce short-term changes in corticospinal excitability in previously sedentary individuals.

Dynamic Postural Stability in Active, Adolescent Males Following Repeated Bouts of Aerobic Exercise in Hot and Temperate Environments: A Pilot Study.

ABSTRACTIntroductionProper jump-landing neuromuscular control is crucial in mitigating lower-extremity musculoskeletal injuries. The presence of fatigue, especially in extreme environments, may degrade dynamic postural stability (DPS) and result in lower-extremity injuries. This study aimed to evaluate the influence of moderate intensity exercise in hot (HOT) and temperate (TEMP) ambient temperatures and residual effects of a previous bout on DPS during a single-legged jump-landing. It was hypothesized that the participants would display worse DPS after HOT compared to TEMP.MethodsSix recreationally active young males (16.8 ± 0.7 year, 1.88 ± 0.12 m, 83.8 ± 19.8 kg) completed two, 60-minute bouts of exercise with 60 minutes of rest between bouts in both HOT (35°C) and TEMP (22.2°C). Heart rate and core body temperature (Tc) were monitored continuously, and DPS was assessed before and after each bout.ResultsThe DPS time and condition effects were not identified (p > 0.05), but HOT elicited some notable (d > 0.20) increases in heart rate, Tc, and DPS compared to TEMP.ConclusionsThe DPS decrements varied between subjects suggesting individual-specific etiology. Repeated bouts of exercise in HOT may place an individual at a greater risk for injury than TEMP if proper prevention strategies are not used.

Accumulation of Skeletal Muscle T Cells and the Repeated Bout Effect in Rats.

The purpose of this investigation was to characterize skeletal muscle T-cell accumulation after contraction-induced muscle damage and test the hypothesis that T cells contribute to postdamage muscle protection (i.e., the repeated bout effect) in a way reminiscent of their role in adaptive immunity. In vivo lengthening contractions were used to model the repeated bout effect and contralateral repeated bout effect in rats. Intramuscular T-cell subsets were characterized by flow cytometry after single and repeated bouts of lengthening contractions, and an adoptive T-cell transfer experiment was done to test whether T cells from muscle damage-experienced rats can confer protection from injury to damage-naive rats. Electrically stimulated lengthening contractions elicited the repeated bout effect, but not the contralateral repeated bout effect. Although leukocytes (CD45+) were scarce in undamaged muscle (2.1% of all cells), substantially more (63% of all cells) were observed after a single bout of lengthening contractions. Within the leukocyte population were several subsets of T cells, including conventional CD4+, CD8+, memory, and regulatory T cells. In contrast, a minimal increase in T cells was observed after a second bout of lengthening contractions. Conventional CD4+ T cells (FoxP3-) were the most abundant subset in muscle after lengthening contractions. Adoptive T-cell transfer from damage-experienced rats did not confer protection to damage-naive recipient rats. The robust T-cell accumulation, particularly the CD4 subset, after contraction-induced damage suggests a role for these cells in muscle repair and adaptation to muscle damaging contractions. Moreover, T cells are unlikely to mediate the protective adaptations of the repeated bout effect in a manner similar to their role in adaptive immunity.

Motor variability in elicited repeated bout rate enhancement is associated with higher sample entropy

In this study we investigated motor variability in individuals who showed (responders) and who did not show (non-responders) a behavioural phenomenon termed repeated bout rate enhancement. The phenomenon is characterized by an increase of the freely chosen index finger tapping rate during the second of two consecutive tapping bouts. It was hypothesized that responders would perform (i) tapping with a lower magnitude, but more complex structure of variability than non-responders and (ii) bout 2 with a lower magnitude and increased complexity of variability than bout 1, as opposed to non-responders. Individuals (n = 102) performed two 3-min tapping bouts separated by 10 min rest. Kinetic and kinematic recordings were performed. Standard deviation (SD), coefficient of variation (CV), and sample entropy (SaEn), representing magnitude and complexity of variability, were computed. For responders, SaEn of vertical displacement of the index finger was higher than for non-responders (p = .046). Further, SaEn of vertical force and vertical displacement was higher in bout 2 than in bout 1 for responders (p < .001 and p = .006, respectively). In general, SD of vertical displacement was lower in bout 2 than in bout 1 (p < .001). SaEn of vertical force was higher in bout 2 than in bout 1 (p = .009). The present lower SD and higher SaEn values of vertical force and displacement time series in bout 2 as compared to bout 1 suggest differences in the dynamics of finger tapping. Further, it is possible that the increases in SaEn of vertical displacement reflected a greater adaptability in the dynamics of motor control among responders compared with non-responders.

Effects of External Counterpulsation on Postexercise Recovery in Elite Rugby League Players.

External counterpulsation (ECP) has previously been used to treat cardiac patients via compression of the lower extremities during diastole to increase venous return and coronary perfusion. However, the effects of ECP on exercise performance and markers of recovery in elite athletes are largely unknown. On 2 separate occasions, 48h apart, 7 elite National Rugby League players performed an identical 60-min field-based conditioning session followed by a 30-min period of either regular ECP treatment or placebo. Power measures during repeated cycle bouts and countermovement jump height and contraction time derivatives were measured at rest and 5h postexercise. Saliva samples and venous blood samples were taken at rest, postexercise, and 5h postexercise to assess stress, inflammation, and muscle damage. After ECP treatment, cycling peak power output (P = .028; 11%) and accumulated peak power (P = .027; 14%) increased compared with the placebo condition. Postexercise plasma interleukin 1 receptor antagonist only increased after ECP (P = .024; 84%), and concentrations of plasma interleukin 1 receptor antagonist tended to be higher (P = .093; 76%) 5 h postexercise. Furthermore, testosterone-to-cortisol ratio was increased above baseline and placebo 5 h postexercise (P = .017-.029; 24-77%). The ratio of postexercise salivary α-amylase to immunoglobulin A decreased after treatment (P = .013; 50%) compared with the placebo control. Exercise performance and hormonal indicators of stress were improved and inflammation markers were reduced following acute ECP.

Repeated bouts of resistance exercise attenuate mitogen-activated protein-kinase signal responses in rat skeletal muscle

Resistance exercise training induces skeletal muscle hypertrophy, but repeated bouts gradually attenuate this anabolic effect. Attenuation of mechanistic target of rapamycin complex 1 (mTORC1) activation by repetitive resistance exercise is involved in this process, but the mechanism leading to inactivation of mTORC1 remains unclear. In this study, we investigated repetition-dependent changes in mitogen-activated protein kinases (MAPKs) and the 90-kDa ribosomal S6 kinase (p90RSK), upstream regulators of mTORC1, in a rat resistance-exercise model. Resistance exercise was associated with increased phosphorylation of 70-kDa ribosomal protein S6 kinase (Thr389), but its magnitude was decreased with repeated bouts. Additionally, phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 (Thr202/Tyr204) and p38 MAPK (Thr180/Tyr182), which are MAPKs, decreased with repeated bouts. A similar result was also observed for p90RSK phosphorylation (Thr573). These observations indicate that repeated bouts desensitized ERK1/2 and p38 MAPK, subsequently attenuating p90RSK phosphorylation. This reduction in p90RSK phosphorylation may have been partly responsible for the blunting of mTORC1 activation by resistance exercise.

Contralateral Effects by Unilateral Eccentric versus Concentric Resistance Training.

Unilateral resistance training increases muscle strength of the contralateral homologous muscle by the cross-education effect. Muscle damage induced by second eccentric exercise bout is attenuated, even when it is performed by the contralateral limb. The present study compared the effects of unilateral eccentric training (ET) and concentric training (CT) of the elbow flexors (EF) on maximal voluntary isometric contraction (MVC) strength and muscle damage of the contralateral untrained EF. Young men were placed into ET, CT, ipsilateral repeated bout (IL-RB), and contralateral repeated bout (CL-RB) groups (n = 12 per group). The ET and CT groups performed unilateral EF training consisting of five sets of six eccentric and concentric contractions, respectively, once a week for 5 wk by increasing the intensity from 10% to 100% of MVC, followed by 30 maximal eccentric contractions (30MaxEC) of the opposite EF 1 wk later. The IL-RB group performed two bouts of 30MaxEC separated by 2 wk using the nondominant arm, and CL-RB group performed two bouts of 30MaxEC with a different arm for each bout in 1-wk apart. The MVC increased (P < 0.05) greater for the trained (19% ± 8%) and untrained (11% ± 5%) arms in ET when compared with those in CT (10% ± 6%, 5% ± 2%). The magnitude of changes in muscle damage markers was reduced by 71% ± 19% after the second than the first bout for IL-RB group, and by 48% ± 21% for CL-RB group. Eccentric training and CT attenuated the magnitude by 58% ± 25% and 13% ± 13%, respectively, and the protective effect of ET was greater (P < 0.05) than CL-RB, but smaller (P < 0.05) than IL-RB. These results showed that cross-education effect was stronger for ET than CT, and progressive ET produced greater contralateral muscle damage protective effect than a single eccentric exercise bout.

Validity of a noninvasive estimation of deep body temperature when wearing personal protective equipment during exercise and recovery

BackgroundDeep body temperature is a critical indicator of heat strain. However, direct measures are often invasive, costly, and difficult to implement in the field. This study assessed the agreement between deep body temperature estimated from heart rate and that measured directly during repeated work bouts while wearing explosive ordnance disposal (EOD) protective clothing and during recovery.MethodsEight males completed three work and recovery periods across two separate days. Work consisted of treadmill walking on a 1% incline at 2.5, 4.0, or 5.5 km/h, in a random order, wearing EOD protective clothing. Ambient temperature and relative humidity were maintained at 24 °C and 50% [Wet bulb globe temperature (WBGT) (20.9 ± 1.2) °C] or 32 °C and 60% [WBGT (29.0 ± 0.2) °C] on the separate days, respectively. Heart rate and gastrointestinal temperature (TGI) were monitored continuously, and deep body temperature was also estimated from heart rate (ECTemp).ResultsThe overall systematic bias between TGI and ECTemp was 0.01 °C with 95% limits of agreement (LoA) of ±0.64 °C and a root mean square error of 0.32 °C. The average error statistics among participants showed no significant differences in error between the exercise and recovery periods or the environmental conditions. At TGI levels of (37.0–37.5) °C, (37.5–38.0) °C, (38.0–38.5) °C, and > 38.5 °C, the systematic bias and ± 95% LoA were (0.08 ± 0.58) °C, (− 0.02 ± 0.69) °C, (− 0.07 ± 0.63) °C, and (− 0.32 ± 0.56) °C, respectively.ConclusionsThe findings demonstrate acceptable validity of the ECTemp up to 38.5 °C. Conducting work within an ECTemp limit of 38.4 °C, in conditions similar to the present study, would protect the majority of personnel from an excessive elevation in deep body temperature (> 39.0 °C).

Oral Glutamine Supplement Reduces Subjective Fatigue Ratings during Repeated Bouts of Firefighting Simulations

Wildland firefighting requires repetitive (e.g., consecutive work shifts) physical work in dangerous conditions (e.g., heat and pollution). Workers commonly enter these environments in a nonacclimated state, leading to fatigue and heightened injury risk. Strategies to improve tolerance to these stressors are lacking. Purpose: To determine if glutamine ingestion prior to and after consecutive days of firefighting simulations in the heat attenuates subjective ratings of fatigue, and evaluate if results were supported by glutamine-induced upregulation of biological stress responses. Methods: Participants (5 male, 3 female) ingested glutamine (0.15 g/kg/day) or a placebo before and after two consecutive days (separated by 24 h) of firefighter simulations in a heated chamber (35 °C, 35% humidity). Perceived fatigue and biological stress were measured pre-, post-, and 4 h postexercise in each trial. Results: Subjective fatigue was reduced pre-exercise on Day 2 in the glutamine group (p &lt; 0.05). Peripheral mononuclear cell expression of heat shock protein 70 (HSP70) and serum antioxidants were elevated at 4 h postexercise on Day 1 in the glutamine trial (p &lt; 0.05). Conclusions: Ingestion of glutamine before and after repeated firefighter simulations in the heat resulted in reduced subjective fatigue on Day 2, which may be a result of the upregulation of biological stress systems (antioxidants, HSPs). This response may support recovery and improve work performance.

Contralateral Repeated Bout Effect of Elbow Flexors Not Observed in Young Women

Previous studies have reported that a prior bout of damaging exercise with one limb attenuated the magnitude of muscle damage in the subsequent damaging exercise with the contralateral limb, a phenomenon called contralateral repeated bout effect (CL-RBE). To our knowledge, these studies involved either exclusively men or a mixture of both sexes. PURPOSE: To determine whether contralateral repeated bout effect of elbow flexors exists in women. METHODS: Twelve healthy women (20.9 ± 2.5 yrs) performed two bouts of 45 maximal eccentric contractions (ECC) of elbow flexors separated by 14 days. The isokinetic muscle strength (60°/sec) was measured pre-exercise, immediately post-exercise, and at 24 and 48 h post-exercise. Limb girth, range of motion (ROM), and muscle soreness were measured pre-exercise, and at 24 and 48 h post-exercise. Surface Electromyography (EMG) was recorded during both exercise bouts from the biceps brachii muscle. Data of all variables were analyzed using two-way repeated measures ANOVA (Bout × Time) except that of median frequency of EMG which was analyzed via paired t-test. RESULTS: The isokinetic strength was significantly reduced after the eccentric exercise for both bout 1 (-19.3 ± 17.4%, P < 0.01) and bout 2 (-15.3 ± 15.2%, P < 0.01). Significant main effects of time were also observed for muscle soreness and ROM. Limb girth did not change significantly after either exercise bout. There were no significant differences between bouts for all the measured variables. CONCLUSION: The CL-RBE of elbow flexors was not evident in healthy young women, which is probably because the magnitude of the muscle damage induced by the first exercise bout was not sufficient to induce protective adaptation for the contralateral arm in the second bout.

An Experimental Group A Streptococcus Vaccine That Reduces Pharyngitis and Tonsillitis in a Nonhuman Primate Model.

Group A Streptococcus (GAS) infections account for an estimated 500,000 deaths every year. This bacterial pathogen is responsible for a variety of mild and life-threatening infections and the triggering of chronic autoimmune sequelae. Pharyngitis caused by group A Streptococcus (GAS), but not asymptomatic GAS carriage, is a prerequisite for acute rheumatic fever (ARF). Repeated bouts of ARF may trigger rheumatic heart disease (RHD), a major cause of heart failure and stroke accounting for 275,000 deaths annually. A vaccine that prevents pharyngitis would markedly reduce morbidity and mortality from ARF and RHD. Nonhuman primates (NHPs) have been utilized to model GAS diseases, and experimentally infected rhesus macaques develop pharyngitis. Here we use an NHP model of GAS pharyngitis to evaluate the efficacy of an experimental vaccine, Combo5 (arginine deiminase [ADI], C5a peptidase [SCPA], streptolysin O [SLO], interleukin-8 [IL-8] protease [SpyCEP], and trigger factor [TF]), specifically designed to exclude GAS components potentially linked to autoimmune complications. Antibody responses against all Combo5 antigens were detected in NHP serum, and immunized NHPs showed a reduction in pharyngitis and tonsillitis compared to controls. Our work establishes the NHP model as a gold standard for the assessment of GAS vaccines.IMPORTANCE GAS-related diseases disproportionally affect disadvantaged populations (e.g., indigenous populations), and development of a vaccine has been neglected. A recent strong advocacy campaign driven by the World Health Organization and the International Vaccine Institute has highlighted the urgent need for a GAS vaccine. One significant obstacle in GAS vaccine development is the lack of a widely used animal model to assess vaccine efficacy. Researchers in the field use a wide range of murine models of infection and in vitro assays, sometimes yielding conflicting results. Here we present the nonhuman primate pharyngeal infection model as a tool to assess vaccine-induced protection against colonization and clinical symptoms of pharyngitis and tonsillitis. We have tested the efficacy of an experimental vaccine candidate with promising results. We believe that the utilization of this valuable tool by the GAS vaccine research community could significantly accelerate the realization of a safe and effective GAS vaccine for humans.

Muscular Preconditioning Using Phototherapy Improves the Physical Work Capacity of the Quadriceps when Applied between Repeated Bouts of Resistance Exercise

Preconditioning skeletal muscle with phototherapy is an experimental technique for producing resistance against muscular fatigue during and after strenuous exercise. This study examined the ergogenic effects of phototherapy when applied intermittently during passive recovery between repeated bouts of isokinetic quadriceps exercise. A triple-blind, repeated measures, placebocontrolled, cross-over design was used in this study to compare the effects of phototherapy on torque/work and power output of the knee extensors in 20 healthy individuals (10 men, 10 women). The exercise protocol consisted of four repeated bouts of isokinetic exercise. Each bout consisted of 30 continuous knee extension concentric contractions at an angular velocity of 75°/s with a 4min recovery interval between bouts. Subjects received active and sham phototherapy in random order during passive recovery between exercise bouts. Phototherapy was administered using a near-infrared laser to the quadriceps femoris muscle group at 10 J/cm2 (total dose of 1600-2400 J). Performance measures included normalized peak torque [Nm/ kg], average peak torque [Nm], total work [Nm], and average power [W]. During the second, third and fourth exercise bouts, subjects produced significantly more torque (normalized and average) and total work/average power output during the active phototherapy condition compared to the sham phototherapy condition. Phototherapy applied as a preconditioning treatment during passive recovery intervals between bouts high of intensity and high volume resistance exercise significantly attenuated fatigue and maintained muscular performance of the quadriceps femoris muscle group. Preconditioning skeletal muscle with phototherapy intermittently during recovery intervals with fatiguing exercise may be a beneficial, non-invasive and safe ergogenic aid for athletes that require high levels of muscular endurance.