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Rebecca Quinlan and Jessica A. Hill

damage differs depending on the exercise stimulus, with endurance modalities associated with high metabolic costs and relatively low mechanical stress 10 compared with eccentric exercise associated with larger mechanical stress. 11 In contrast to this, intermittent exercise is shown to induce both

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Shannon S. Block, Trevor R. Tooley, Matthew R. Nagy, Molly P. O’Sullivan, Leah E. Robinson, Natalie Colabianchi and Rebecca E. Hasson

acute effects of action-based video game play and intermittent exercise, performed at varying intensities (low, moderate, and high) on math performance in preadolescent children. Based on the findings of Phillips and Castelli ( 26 ), it was hypothesized that high-intensity exercise breaks would elicit a

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Gerhard Tschakert and Peter Hofmann

High-intensity intermittent exercise (HIIE) has been applied in competitive sports for more than 100 years. In the last decades, interval studies revealed a multitude of beneficial effects in various subjects despite a large variety of exercise prescriptions. Therefore, one could assume that an accurate prescription of HIIE is not relevant. However, the manipulation of HIIE variables (peak workload and peak-workload duration, mean workload, intensity and duration of recovery, number of intervals) directly affects the acute physiological responses during exercise leading to specific medium- and long-term training adaptations. The diversity of intermittent-exercise regimens applied in different studies may suggest that the acute physiological mechanisms during HIIE forced by particular exercise prescriptions are not clear in detail or not taken into consideration. A standardized and consistent approach to the prescription and classification of HIIE is still missing. An optimal and individual setting of the HIIE variables requires the consideration of the physiological responses elicited by the HIIE regimen. In this regard, particularly the intensities and durations of the peak-workload phases are highly relevant since these variables are primarily responsible for the metabolic processes during HIIE in the working muscle (eg, lactate metabolism). In addition, the way of prescribing exercise intensity also markedly influences acute metabolic and cardiorespiratory responses. Turn-point or threshold models are suggested to be more appropriate and accurate to prescribe HIIE intensity than using percentages of maximal heart rate or maximal oxygen uptake.

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Al Haddad Hani, Paul B. Laursen, Ahmaidi Said and Buchheit Martin

Purpose:

To assess the effect of supramaximal intermittent exercise on long-term cardiac autonomic activity, inferred from heart rate variability (HRV).

Methods:

Eleven healthy males performed a series of two consecutive intermittent 15-s runs at 95% VIFT (i.e., speed reached at the end of the 30-15 Intermittent Fitness Test) interspersed with 15 s of active recovery at 45% VIFT until exhaustion. Beat-to-beat intervals were recorded during two consecutive nights (habituation night and 1st night) before, 10 min before and immediately after exercise, as well as 12 h (2nd night) and 36 h (3rd night) after supramaximal intermittent exercise. The HRV indices were calculated from the last 5 min of resting and recovery periods, and the first 10 min of the first estimated slow wave sleep period.

Results:

Immediate post-supramaximal exercise vagal-related HRV indices were significantly lower than immediate pre-supramaximal exercise values (P < .001). Most vagal-related indices were lower during the 2nd night compared with the 1st night (eg, mean RR intervals, P = .03). Compared with the 2nd night, vagal-related HRV indices were significantly higher during the 3rd night. Variables were not different between the 1st and 3rd nights; however, we noted a tendency (adjusted effect size, aES) for an increased normalized high-frequency component (P = .06 and aES = 0.70) and a tendency toward a decreased low-frequency component (P = .06 and aES = 0.74).

Conclusion:

Results confirm the strong influence of exercise intensity on short- and long-term post exercise heart rate variability recovery and might help explain the high efficiency of supramaximal training for enhancing indices of cardiorespiratory fitness.

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Nicolette C. Bishop, Michael Gleeson, Ceri W. Nicholas and Ajmol Ali

Ingesting carbohydrate (CHO) beverages during prolonged, continuous heavy exercise results in smaller changes in the plasma concentrations of several cytokines and attenuates a decline in neutrophil function. In contrast, ingesting CHO during prolonged intermittent exercise appears to have negligible influence on these responses, probably due to the overall moderate intensity of these intermittent exercise protocols. Therefore, we examined the effect of CHO ingestion on plasma interIeukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and lipopolysaccharide (LPS)-stimuIated neutrophil degranulation responses to high-intensity intermittent running. Six trained male soccer players performed 2 exercise trials, 7 days apart, in a randomized, counterbalanced design. On each occasion, they completed six 15-min periods of intermittent running consisting of maximal sprinting interspersed with less intense periods of running and walking. Subjects consumed either CHO or artificially sweetened placebo(PLA) beverages immediately before and at 15-min intervals during the exercise. At 30 min post-exercise, CHO versus PLA was associated with a higher plasma glucose concentration (p< .01), a lower plasma cortisol and IL-6 concentration (p < .02), and fewer numbers of circulating neutrophils (p < .05). Following the exercise, LPS-stimulated elastase release per neutrophil fell 31 % below baseline values on the PLA trial (p = .06) compared with 11% on the CHO trial (p = .30). Plasma TNF-α concentration increased following the exercise (main effect of time, p < .001) but was not affected by CHO. These data indicate that CHO ingestion attenuates changes in plasma IL-6 concentration, neutrophil trafficking, and LPS-stimulated neutrophil degranulation in response to intermittent exercise that involves bouts of very high intensity exercise.

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Jonathan P. Little, Philip D. Chilibeck, Dawn Ciona, Albert Vandenberg and Gordon A. Zello

The glycemic index (GI) of a pre exercise meal may affect substrate utilization and performance during continuous exercise.

Purpose:

To examine the effects of low- and high-GI foods on metabolism and performance during high-intensity, intermittent exercise.

Methods:

Seven male athletes participated in three experimental trials (low-GI, high-GI, and fasted control) separated by ~7 days. Foods were consumed 3 h before (~1.3 g·kg−1 carbohydrate) and halfway through (~0.2 g·kg−1 carbohydrate) 90 min of intermittent treadmill running designed to simulate the activity pattern of soccer. Expired gas was collected during exercise to estimate substrate oxidation. Performance was assessed by the distance covered on fve 1-min sprints during the last 15 min of exercise.

Results:

Respiratory exchange ratio was higher and fat oxidation lower during exercise in the high-GI condition compared with fasting (P < .05). The mean difference in total distance covered on the repeated sprint test between low GI and fasting (247 m; 90% confidence limits ±352 m) represented an 81% (likely, probable) chance that the low-GI condition improved performance over fasting. The mean difference between high GI and fasted control (223 m; ±385 m) represented a 76% (likely, probable) chance of improved performance. There were no differences between low and high GI.

Conclusions:

When compared with fasting, both low- and high-GI foods consumed 3 h before and halfway through prolonged, high-intensity intermittent exercise improved repeated sprint performance. High-GI foods impaired fat oxidation during exercise but the GI did not appear to influence high-intensity, intermittent exercise performance.

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Randy J. Schmitz, John C. Cone, Timothy J. Copple, Robert A. Henson and Sandra J. Shultz

Context:

Potential biomechanical compensations allowing for maintenance of maximal explosive performance during prolonged intermittent exercise, with respect to the corresponding rise in injury rates during the later stages of exercise or competition, are relatively unknown.

Objective:

To identify lower-extremity countermovement-jump (CMJ) biomechanical factors using a principal-components approach and then examine how these factors changed during a 90-min intermittent-exercise protocol (IEP) while maintaining maximal jump height.

Design:

Mixed-model design.

Setting:

Laboratory.

Participants:

Fifty-nine intermittent-sport athletes (30 male, 29 female) participated in experimental and control conditions.

Interventions:

Before and after a dynamic warm-up and every 15 min during the 1st and 2nd halves of an individually prescribed 90-min IEP, participants were assessed on rating of perceived exertion, sprint/cut speed, and 3-dimensional CMJ biomechanics (experimental). On a separate day, the same measures were obtained every 15 min during 90 min of quiet rest (control).

Main Outcome Measures:

Univariate piecewise growth models analyzed progressive changes in CMJ performance and biomechanical factors extracted from a principal-components analysis of the individual biomechanical dependent variables.

Results:

While CMJ height was maintained during the 1st and 2nd halves, the body descended less and knee kinetic and energetic magnitudes decreased as the IEP progressed.

Conclusions:

The results indicate that vertical-jump performance is maintained along with progressive biomechanical changes commonly associated with decreased performance. A better understanding of lower-extremity biomechanics during explosive actions in response to IEP allows us to further develop and individualize performance training programs.

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Martin Tan, Rachel Chan Moy Fat, Yati N. Boutcher and Stephen H. Boutcher

High-intensity intermittent exercise (HIIE) such as the 30-s Wingate test attenuates postprandial triacylglycerol (TG), however, the ability of shorter versions of HIIE to reduce postprandial TG is undetermined. Thus, the effect of 8-s sprinting bouts of HIIE on blood TG levels of 12 females after consumption of a high-fat meal (HFM) was examined. Twelve young, sedentary women (BMI 25.1 ± 2.3 kg/m2; age 21.3 ± 2.1 years) completed a maximal oxygen uptake test and then on different days underwent either an exercise or a no-exercise postprandial TG condition. Both conditions involved consuming a HFM after a 12-hr fast. The HFM, in milkshake form provided 4170 kJ (993 Kcal) of energy and 98 g fat. Order was counter-balanced. In the exercise condition participants completed 20-min of HIIE cycling consisting of repeated bouts of 8 s sprint cycling (100–115 rpm) and 12 s of active rest (easy pedaling) 14 hr before consuming the HFM. Blood samples were collected hourly after the HFM for 4 hr. Total postprandial TG was 13% lower, p = .004, in the exercise (5.84 ± 1.08 mmol L−1 4 h−1) compared with the no-exercise condition (6.71 ± 1.63 mmol L−1 4 h−1). In conclusion, HIIE significantly attenuated postprandial TG in sedentary young women.

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Jonathan P. Little, Philip D. Chilibeck, Dawn Ciona, Scott Forbes, Huw Rees, Albert Vandenberg and Gordon A. Zello

Consuming carbohydrate-rich meals before continuous endurance exercise improves performance, yet few studies have evaluated the ideal preexercise meal for high-intensity intermittent exercise, which is characteristic of many team sports. The authors’ purpose was to investigate the effects of low- and high-glycemic-index (GI) meals on metabolism and performance during high-intensity, intermittent exercise. Sixteen male participants completed three 90-min high-intensity intermittent running trials in a single-blinded random order, separated by ~7 d, while fasted (control) and 2 hr after ingesting an isoenergetic low-GI (lentil), or high-GI (potato and egg white) preexercise meal. Serum free fatty acids were higher and insulin lower throughout exercise in the fasted condition (p < .05), but there were no differences in blood glucose during exercise between conditions. Distance covered on a repeated-sprint test at the end of exercise was significantly greater in the low-GI and high-GI conditions than in the control (p < .05). Rating of perceived exertion was lower in the low-GI condition than in the control (p = .01). In a subsample of 5 participants, muscle glycogen availability was greater in the low- and high-GI conditions versus fasted control before the repeated-sprint test (p < .05), with no differences between low and high GI. When exogenous carbohydrates are not provided during exercise both low- and high-GI preexercise meals improve high-intensity, intermittent exercise performance, probably by increasing the availability of muscle glycogen. However, the GI does not influence markers of substrate oxidation during high-intensity, intermittent exercise.

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Stephen A. Mears and Susan M. Shirreffs

Water intake occurs following a period of high-intensity intermittent exercise (HIIE) due to sensations of thirst yet this does not always appear to be caused by body water losses. Thus, the aim was to assess voluntary water intake following HIIE. Ten healthy males (22 ± 2 y, 75.6 ± 6.9 kg, VO2peak 57.3 ± 11.4 m·kg−1·min−1; mean± SD) completed two trials (7–14 d apart). Subjects sat for 30 min then completed an exercise period involving 2 min of rest followed by 1 min at 100% VO2peak repeated for 60 min (HIIE) or 60 min continuously at 33% VO2peak (LO). Subjects then sat for 60 min and were allowed ad libitum water intake. Body mass was measured at start and end of trials. Serum osmolality, blood lactate, and sodium concentrations, sensations of thirst and mouth dryness were measured at baseline, postexercise and after 5, 15, 30, and 60 min of recovery. Vasopressin concentration was measured at baseline, postexercise, 5 min, and 30 min. Body mass loss over the whole trial was similar (HIIE: 0.77 ± 0.50; LO: 0.85 ± 0.55%; p = .124). Sweat lost during exercise (0.78 ± 0.22 vs. 0.66 ± 0.26 L) and voluntary water intake during recovery (0.416 ± 0.299 vs. 0.294 ± 0.295 L; p < .05) were greater in HIIE. Serum osmolality (297 ± 3 vs. 288 ± 4mOsmol·kg−1), blood lactate (8.5 ± 2.7 vs. 0.7 ± 0.4 mmol·L−1), serum sodium (146 ± 1 vs. 143 ± 1 mmol·L−1) and vasopressin (9.91 ± 3.36 vs. 4.43 ± 0.86 pg·ml−1) concentrations were higher after HIIE (p < .05) and thirst (84 ± 7 vs. 60 ± 21) and mouth dryness (87 ± 7 vs. 64 ± 23) also tended to be higher (p = .060). Greater voluntary water intake after HIIE was mainly caused by increased sweat loss and the consequences of increased serum osmolality mainly resulting from higher blood lactate concentrations.