nutritional intake influences any GI disturbance induced by high-intensity exercise in the heat. This information could assist sports dietitians in advising athletes during preparation for training and competition in hot conditions. Methods Experimental Design A randomized crossover trial was used to
Naroa Etxebarria, Nicole A. Beard, Maree Gleeson, Alice Wallett, Warren A. McDonald, Kate L. Pumpa, and David B. Pyne
Jos J. de Koning, Dionne A. Noordhof, Tom P. Uitslag, Rianna E Galiart, Christopher Dodge, and Carl Foster
Gross efficiency (GE) is coupling power production to propulsion and is an important performance-determining factor in endurance sports. Measuring GE normally requires measuring VO2 during submaximal exercise. In this study a method is proposed to estimating GE during high-intensity exercise.
Nineteen subjects completed a maximal incremental test and 2 GE tests (1 experimental and 1 control test). The GE test consisted of 10 min cycling at 50% peak power output (PPO), 2 min at 25 W, followed by 4 min 100% PPO, 1 min at 25 W, and another 10 min at 50% PPO. GE was determined for the 50%-PPO sections and was, for the second 50%-PPO section, back-extrapolated, using linear regression, to the end of the 100%-PPO bout.
Back-extrapolation of the GE data resulted in a calculated GE of 15.8% ± 1.7% at the end of the 100%-PPO bout, in contrast to 18.3% ± 1.3% during the final 2 min of the first 10-min 50%-PPO bout.
Back-extrapolation seems valuable in providing more insight in GE during high-intensity exercise.
Tiago Peçanha, Marcelle Paula-Ribeiro, Edson Campana-Rezende, Rhenan Bartels, João Carlos Bouzas Marins, and Jorge Roberto Perrout de Lima
It has been shown that water intake (WI) improves postexercise parasympathetic recovery after moderateintensity exercise session. However, the potential cardiovascular benefit promoted by WI has not been investigated after high-intensity exercise.
To assess the effects of WI on post high-intensity parasympathetic recovery.
Twelve recreationally active young men participated in the study (22 ± 1.4 years, 24.1 ± 1.6 kg.m−2). The experimental protocol consisted of two visits to the laboratory. Each visit consisted in the completion of a 30-min high-intensity [~80% of maximal heart rate (HR)] cycle ergometer aerobic session performing randomly the WI or control (CON, no water consumption) intervention at the end of the exercise. HR and RR intervals (RRi) were continuously recorded by a heart rate monitor before, during and after the exercise. Differences in HR recovery [e.g., absolute heart rate decrement after 1 min of recovery (HRR60s) and time-constant of the first order exponential fitting curve of the HRR (HRRτ)] and in postexercise vagalrelated heart rate variability (HRV) indexes (rMSSD30s, rMSSD, pNN50, SD1 and HF) were calculated and compared for WI and CON.
A similar HR recovery and an increased postexercise HRV [SD1 = 9.4 ± 5.9 vs. 6.0 ± 3.9 millisecond, HF(ln) = 3.6 ± 1.4 vs. 2.4 ± 1.3 millisecond2, for WI and CON, respectively; p < .05] was observed in WI compared with CON.
The results suggest that WI accelerates the postexercise parasympathetic reactivation after high-intensity exercise. Such outcome reveals an important cardioprotective effect of WI.
Mark A. Tarnopolsky and Dan P. MacLennan
Creatine monohydrate supplementation has been shown to enhance high-intensity exercise performance in some but not all studies. Part of the controversy surrounding the ergogenic effect(s) of creatine monohydrate supplementation may relate to design issues that result in low statistical power. A further question that remains unresolved in the creatine literature is whether or not males and females respond in a similar manner to supplementation. We studied the effect of creatine supplementation upon high intensity exercise performance in 24 subjects (n = 12 males, n = 12 females). Creatine monohydrate (Cr; 5g, 4x/d × 4d) and placebo (PI; glucose polymer × 4d) were provided using a randomized. double-blind crossover design (7 week washout). Outcome measures included: 2 × 30-S anaerobic cycle lest, with plasma lactate pre- and post-test; dorsi-flexor: maximal voluntary contraction (MVC), 2-min fatigue test, and electrically stimulated peak and tetanic torque; isokinetic knee extension torque and I -min ischeniic handgrip strength. Significant main effects of Cr treatment included: increased peak and relative peak anaerobic cycling power (↑3.7%; p < .05), dorsi-flexion MVC torque (↑6.6% p < .05), and increased lactate (↑20.8%; p < .05) with no gender specific responses. We concluded that short-term Cr supplementation can increase indices of high-intensity exercise performance for both males and females.
Takaaki Mishima, Takashi Yamada, Makoto Sakamoto, Minako Sugiyama, Satoshi Matsunaga, Hirohiko Maemura, Muneshige Shimizu, Yoshihisa Takahata, Fumiki Morimatsu, and Masanobu Wada
This study was conducted to determine whether dietary chicken-breast extract (CBEX), a rich source of histidine-containing dipeptides, could modify exerciseinduced changes in sarcoplasmic reticulum (SR) function. After 5 weeks of dietary CBEX, SR Ca2+-handling ability was examined in the vastus lateralis muscles of rats subjected to high-intensity running for 2.5 min. Dietary CBEX caused an approximately 15% and 45% increase (p < .01) in muscle carnosine and anserine concentrations, respectively. In resting muscles, depressions in SR Ca2+–ATPase activity were evoked by dietary CBEX without concomitant changes in SR Ca2+ uptake and release rates. The data confirm that high-intensity exercise depresses SR Ca2+ handling. In spite of the same run time, SR Ca2+ handling was reduced to a lesser degree in muscles of CBEX-containing-chow-fed rats than in standard-chow-fed rats (p < .05). These results suggest that dietary CBEX might attenuate deteriorations in SR Ca2+-handling ability that occur with high-intensity exercise.
Todd A. Astorino, Michael N. Terzi, Daniel W. Roberson, and Timothy R. Burnett
Caffeine has been shown to reduce leg-muscle pain during submaximal cycle ergometry, as well as in response to eccentric exercise. However, less is known about its analgesic properties during non-steadystate, high-intensity exercise. The primary aim of this study was to examine the effect of 2 doses of caffeine on leg pain and rating of perceived exertion (RPE) during repeated bouts of high-intensity exercise. Fifteen active men (age 26.4 ± 3.9 yr) completed 2 bouts of 40 repetitions of “all-out” knee extension and flexion of the dominant leg at a contraction velocity equal to 180°/s. Before each trial, subjects abstained from caffeine intake and intense exercise for 48 hr. Over 3 days separated by 48 hr, subjects ingested 1 of 3 treatments (5 mg/kg or 2 mg/kg of anhydrous caffeine or placebo) in a randomized, single-blind, counterbalanced, crossover design. Leg-muscle pain and RPE were assessed during and after exercise using established categorical scales. Across all treatments, pain perception was significantly increased (p < .05) during exercise, as well as from Bout 1 to 2, yet there was no effect (p > .05) of caffeine on pain perception or RPE. Various measures of muscle function were improved (p < .05) with a 5-mg/kg caffeine dose vs. the other treatments. In the 5-mg/kg trial, it is plausible that subjects were able to perform better with similar levels of pain perception and exertion.
David M. Morris, Rebecca S. Shafer, Kimberly R. Fairbrother, and Mark W. Woodall
The authors sought to determine the effects of oral lactate consumption on blood bicarbonate (HCO3−) levels, pH levels, and performance during high-intensity exercise on a cycle ergometer. Subjects (N = 11) were trained male and female cyclists. Time to exhaustion (TTE) and total work were measured during high-intensity exercise bouts 80 min after the consumption of 120 mg/kg body mass of lactate (L), an equal volume of placebo (PL), or no treatment (NT). Blood HCO3− increased significantly after ingestion of lactate (p < .05) but was not affected in PL or NT (p > .05). No changes in pH were observed as a result of treatment. TTE and total work during the performance test increased significantly by 17% in L compared with PL and NT (p = .02). No significant differences in TTE and total work were seen between the PL and NT protocols (p = .85). The authors conclude that consuming 120 mg/kg body mass of lactate increases HCO3− levels and increases exercise performance during high-intensity cycling ergometry to exhaustion.
Xiaocai Shi, Mary K. Horn, Kris L. Osterberg, John R. Stofan,, Jeffrey J. Zachwieja, Craig A. Horswill, Dennis H. Passe, and Robert Murray
This study investigated whether different beverage carbohydrate concentration and osmolality would provoke gastrointestinal (GI) discomfort during intermittent, high-intensity exercise. Thirty-six adult and adolescent athletes were tested on separate days in a double-blind, randomized trial of 6% and 8% carbohydrate-electrolytes (CHO-E) beverages during four 12-min quarters (Q) of circuit training that included intermittent sprints, lateral hops, shuttle runs, and vertical jumps. GI discomfort and fatigue surveys were completed before the first Q and immediately after each Q. All ratings of GI discomfort were modest throughout the study. The cumulative index for GI discomfort, however, was greater for the 8% CHO-E beverage than for the 6% CHO-E beverage at Q3 and Q4 (P < 0.05). Averaging across all 4 quarters, the 8% CHO-E treatment produced significantly higher mean ratings of stomach upset and side ache. In conclusion, higher CHO concentration and osmolality in an ingested beverage provokes stomach upset and side ache.
Christina Åsan Grasaas, Gertjan Ettema, Ann Magdalen Hegge, Knut Skovereng, and Øyvind Sandbakk
This study investigated changes in technique and efficiency after high-intensity exercise to exhaustion in elite cross-country skiers. Twelve elite male skiers completed 4 min submaximal exercise before and after a high-intensity incremental test to exhaustion with the G3 skating technique on a 5% inclined roller-ski treadmill. Kinematics and kinetics were monitored by instrumented roller skis, work rate was calculated as power against roller friction and gravity, aerobic metabolic cost was determined from gas exchange, and blood lactate values indicated the anaerobic contribution. Gross efficiency was the work rate divided by aerobic metabolic rate. A recovery period of 10 min between the incremental test and the posttest was included to allow the metabolic values to return to baseline. Changes in neuromuscular fatigue in upper and lower limbs before and after the incremental test were indicated by peak power in concentric bench press and squat-jump height. From pretest to posttest, cycle length decreased and cycle rate increased by approximately 5% (P < 0.001), whereas the amount of ski forces did not change significantly. Oxygen uptake increased by 4%, and gross efficiency decreased from 15.5% ± 0.7% to 15.2% ± 0.5% from pretest to posttest (both P < .02). Correspondingly, blood lactate concentration increased from 2.4 ± 1.0 to 6.2 ± 2.5 mmol/L (P < .001). Bench-press and squat-jump performance remained unaltered. Elite cross-country skiers demonstrated a less efficient technique and shorter cycle length during submaximal roller-ski skating after high-intensity exercise. However, there were no changes in ski forces or peak power in the upper and lower limbs that could explain these differences.
Stuart D.R. Galloway, Matthew J.E. Lott, and Lindsay C. Toulouse
The present study aimed to investigate the influence of timing of preexercise carbohydrate feeding (Part A) and carbohydrate concentration (Part B) on short-duration high-intensity exercise capacity. In Part A, 17 males, and in Part B 10 males, performed a peak power output (PPO) test, two familiarization trials at 90% of PPO, and 4 (for Part A) or 3 (for Part B) experimental trials involving exercise capacity tests at 90% PPO. In Part A, the 4 trials were conducted following ingestion of a 6.4% carbohydrate/electrolyte sports drink ingested 30 (C30) or 120 (C120) minutes before exercise, or a flavor-matched placebo administered either 30 (P30) or 120 (P120) minutes before exercise. In Part B, the 3 trials were performed 30 min after ingestion of 0%, 2% or 12% carbohydrate solutions. All trials were performed in a double-blind cross-over design following and overnight fast. Dietary intake and activity in the 2 days before trials was recorded and replicated on each visit. Glucose, lactate, heart rate, and mood/arousal were recorded at intervals during the trials. In Part A, C30 produced the greatest exercise capacity (mean ± SD; 9.0 ± 1.9 min, p < .01) compared with all other trials (7.7 ± 1.5 min P30, 8.0 ± 1.7 min P120, 7.9 ± 1.9 min C120). In Part B, exercise capacity (min) following ingestion of the 2% solution (9.2 ± 2.1) compared with 0% (8.2 ± 0.7) and 12% (8.0 ± 1.3) solutions approached significance (p = .09). This study provides new evidence to suggest that timing of carbohydrate intake is important in short duration high-intensity exercise tasks, but a concentration effect requires further exploration.