Two weeks of reduced-volume sprint interval or traditional exercise training does not improve metabolic functioning in sedentary obese men

AIMS

To investigate the effects of short-term, reduced-volume sprint interval training (SIT) compared to traditional exercise recommendations (TER) in sedentary obese men.

METHODS

Sixteen subjects [37.8 ± 5.8 years; body mass index (BMI) 32.8 ± 4.7 kg/m(2)] were randomly allocated to 2 weeks of either SIT (6 sessions of 8-12 × 10 s sprints) or TER [10 sessions of 30 min at 65% peak oxygen consumption (VO(2peak))] cycle exercise. Fasting plasma glucose, insulin, non-esterified fatty acids (NEFA), homeostasis model assessment of insulin sensitivity (HOMA-IR), body composition and VO(2peak) were assessed at baseline and approximately 72 h after the final training bout. Skeletal muscle biopsy samples were also obtained before and 72 h after training and analysed for AS160 phosphorylation and COX II, COX IV, GLUT-4, Nur77 and SIRT1 protein expression.

RESULTS

No changes in BMI, body composition, VO(2peak), glucose, insulin, NEFA and HOMA-IR were observed after training, either within or between groups. Skeletal muscle markers of glucose metabolism and mitochondrial function also remained unaltered after 2 weeks of exercise training.

CONCLUSIONS

Our findings show that 2 weeks of reduced-volume SIT or TER did not elicit any measurable metabolic adaptations in sedentary obese men. Further work is needed to determine the minimal amount of exercise required for short-term adaptations in this population.

Reliability of resting and postexercise heart rate measures

In this study, we compared the reliability of short-term resting heart rate (HR) variability (HRV) and postexercise parasympathetic reactivation (i.e., HR recovery (HRR) and HRV) indices following either submaximal or supramaximal exercise. On 4 different occasions, beat-to-beat HR was recorded in 15 healthy males (21.5 ± 1.4 yr) during 5 min of seated rest, followed by submaximal (Sub) and supramaximal (Supra) exercise bouts; both exercise bouts were followed by 5 min of seated recovery. Reliability of all HR-derived indices was assessed by the typical error of measurement expressed as a coefficient of variation (CV,%). CV for HRV indices ranged from 4 to 17%, 7 to 27% and 41 to 82% for time domain, spectral and ratio indices, respectively. The CV for HRR ranged from 15 to 32%. Spectral CVs for HRV were lower at rest compared with Supra (e.g., natural logarithm of the high frequency range (LnHF); 12.6 vs. 26.2%; P=0.02). HRR reliability was not different between Sub and Supra (25 vs. 14%; P=0.10). The present study found discrepancy in the CVs of vagal-related heart rate indices; a finding that should be appreciated when assessing changes in these variables. Further, Supra exercise was shown to worsen the reliability of HRV-spectral indices.

Training for intense exercise performance: high-intensity or high-volume training?

Performance in intense exercise events, such as Olympic rowing, swimming, kayak, track running and track cycling events, involves energy contribution from aerobic and anaerobic sources. As aerobic energy supply dominates the total energy requirements after ∼75s of near maximal effort, and has the greatest potential for improvement with training, the majority of training for these events is generally aimed at increasing aerobic metabolic capacity. A short-term period (six to eight sessions over 2-4 weeks) of high-intensity interval training (consisting of repeated exercise bouts performed close to or well above the maximal oxygen uptake intensity, interspersed with low-intensity exercise or complete rest) can elicit increases in intense exercise performance of 2-4% in well-trained athletes. The influence of high-volume training is less discussed, but its importance should not be downplayed, as high-volume training also induces important metabolic adaptations. While the metabolic adaptations that occur with high-volume training and high-intensity training show considerable overlap, the molecular events that signal for these adaptations may be different. A polarized approach to training, whereby ∼75% of total training volume is performed at low intensities, and 10-15% is performed at very high intensities, has been suggested as an optimal training intensity distribution for elite athletes who perform intense exercise events.

Cardiac autonomic responses to repeated shuttle sprints

Team sport match play requires athletes to perform a number of repeated shuttle sprints. However, the acute effects of these repeated sprint sequences on lactic acidosis and resulting autonomic state perturbation are not known. The aim of this study was to observe and compare the blood lactate and post-exercise cardiac autonomic responses of a repeated shuttle-sprint ability test with the 30-15 Intermittent Fitness Test (30-15 (IFT)); the latter test representing a standard for exhaustive supramaximal effort. Thirteen adult team sport players performed the repeated shuttle-sprint ability test and the 30-15 (IFT) on separate days in a counter-balanced order. The repeated shuttle-sprint ability test consisted of six repetitions of maximal 2x15 m shuttle sprints ( approximately 5 s) departing every 20 s, while the 30-15 (IFT) involved progressive 30 s shuttle runs interspersed with 15 s of passive recovery until exhaustion. Blood lactate was measured before and after the tests, while autonomic responses were assessed using immediate heart rate recovery and heart rate variability indices. Peak blood lactate (10.6+/-2.1 vs. 10.2+/-2.8 mM) and heart beats recovered in one minute after exercise cessation (36.4+/-7.8 vs. 39.3+/-7.9 bpm) were similar after both the repeated shuttle-sprint ability test and the 30-15 (IFT). With the exception of the vagal-related time-varying root mean square of successive R-R interval differences at each 30 s, which recovered earlier after the repeated shuttle-sprint ability test compared with 30-15 (IFT), all heart rate variability indices decreased similarly after both tests in comparison to baseline values. In conclusion, the repeated shuttle-sprint ability test was shown to induce comparable levels of lactic acidosis and post-exercise autonomic state as the 30-15 (IFT). These levels of metabolic and autonomic states are likely to occur during team sport match play.

Muscle deoxygenation during repeated sprint running: Effect of active vs. passive recovery

The purpose of this study was to compare the effect of active (AR) versus passive recovery (PR) on muscle deoxygenation during short repeated maximal running. Ten male team sport athletes (26.9+/-3.7y) performed 6 repeated maximal 4-s sprints interspersed with 21 s of either AR (2 m.s (-1)) or PR (standing) on a non-motorized treadmill. Mean running speed (AvSp (mean)), percentage speed decrement (Sp%Dec), oxygen uptake (V O (2)), deoxyhemoglobin (HHb) and blood lactate ([La] (b)) were computed for each recovery condition. Compared to PR, AvSp (mean) was lower (3.79+/-0.28 vs. 4.09+/-0.32m.s (-1); P<0.001) and Sp%Dec higher (7.2+/-3.7 vs. 3.2+/-0.1.3%; P<0.001) for AR. Mean V O (2) (3.64+/-0.44 vs. 2.91+/-0.47L.min (-1), P<0.001), HHb (94.4+/-16.8 vs. 83.4+/-4.8% of HHb during the first sprint, P=0.02) and [La] (b) (13.5+/-2.5 vs. 12.7+/-2.2 mmol.l (-1), P=0.03) were significantly higher during AR compared to PR. In conclusion, during run-based repeated sprinting, AR was associated with reduced repeated sprint ability and higher muscle deoxygenation.

Influence of starting strategy on cycling time trial performance in the heat

The purpose of this study was to determine the influence of starting strategy on time trial performance in the heat. Eleven endurance trained male cyclists (30+/-5 years, 79.5+/-4.6 kg, VO(2max) 58.5+/-5.0 ml x kg x (-1) min(-1)) performed four 20-km time trials in the heat (32.7+/-0.7 degrees C and 55% relative humidity). The first time trial was completed at a self-selected pace (SPTT). During the following time trials, subjects performed the initial 2.5-km at power outputs 10% above (10% ATT), 10% below (10% BTT) or equal (ETT) to that of the average power during the initial 2.5-km of the self-selected trial; the remaining 17.5-km was self-paced. Throughout each time trial, power output, rectal temperature, skin temperature, heat storage, pain intensity and thermal sensation were taken. Despite significantly (P<0.05) greater power outputs for 10% BTT (273+/-45W) compared with the ETT (267+/-48W) and 10% ATT (265+/-41W) during the final 17.5-km, overall 20-km performance time was not significantly different amongst trials. There were no differences in any of the other measured variables between trials. These data show that varying starting power by +/-10% did not affect 20 km time trial performance in the heat.

Game-based training in young elite handball players

This study compared the effect of high-intensity interval training (HIT) versus specific game-based handball training (HBT) on handball performance parameters. Thirty-two highly-trained adolescents (15.5+/-0.9 y) were assigned to either HIT (n=17) or HBT (n=15) groups, that performed either HIT or HBT twice per week for 10 weeks. The HIT consisted of 12-24 x 15 s runs at 95% of the speed reached at the end of the 30-15 Intermittent Fitness Test (V(IFT)) interspersed with 15 s passive recovery, while the HBT consisted of small-sided handball games performed over a similar time period. Before and after training, performance was assessed with a counter movement jump (CMJ), 10 m sprint time (10 m), best (RSAbest) and mean (RSAmean) times on a repeated sprint ability (RSA) test, the V(IFT) and the intermittent endurance index (iEI). After training, RSAbest (-3.5+/-2.7%), RSAmean (-3.9+/-2.2%) and V(IFT) (+6.3+/-5.2%) were improved (P<0.05), but there was no difference between groups. In conclusion, both HIT and HBT were found to be effective training modes for adolescent handball players. However, HBT should be considered as the preferred training method due to its higher game-based specificity.

Effect of cold water immersion on postexercise parasympathetic reactivation

The aim of the present study was to assess the effect of cold water immersion (CWI) on postexercise parasympathetic reactivation. Ten male cyclists (age, 29 +/- 6 yr) performed two repeated supramaximal cycling exercises (SE(1) and SE(2)) interspersed with a 20-min passive recovery period, during which they were randomly assigned to either 5 min of CWI in 14 degrees C or a control (N) condition where they sat in an environmental chamber (35.0 +/- 0.3 degrees C and 40.0 +/- 3.0% relative humidity). Rectal temperature (T(re)) and beat-to-beat heart rate (HR) were recorded continuously. The time constant of HR recovery (HRRtau) and a time (30-s) varying vagal-related HR variability (HRV) index (rMSSD(30s)) were assessed during the 6-min period immediately following exercise. Resting vagal-related HRV indexes were calculated during 3-min periods 2 min before and 3 min after SE(1) and SE(2). Results showed no effect of CWI on T(re) (P = 0.29), SE performance (P = 0.76), and HRRtau (P = 0.61). In contrast, all vagal-related HRV indexes were decreased after SE(1) (P < 0.001) and tended to decrease even further after SE(2) under N condition but not with CWI. When compared with the N condition, CWI increased HRV indexes before (P < 0.05) and rMSSD(30s) after (P < 0.05) SE(2). Our study shows that CWI can significantly restore the impaired vagal-related HRV indexes observed after supramaximal exercise. CWI may serve as a simple and effective means to accelerate parasympathetic reactivation during the immediate period following supramaximal exercise.

Effect of a 5-min cold-water immersion recovery on exercise performance in the heat

BACKGROUND

This study examined the effect of a 5-min cold-water immersion (14 degrees C) recovery intervention on repeated cycling performance in the heat.

METHODS

10 male cyclists performed two bouts of a 25-min constant-paced (254 (22) W) cycling session followed by a 4-km time trial in hot conditions (35 degrees C, 40% relative humidity). The two bouts were separated by either 15 min of seated recovery in the heat (control) or the same condition with 5-min cold-water immersion (5th-10th minute), using a counterbalanced cross-over design (CP(1)TT(1) --> CWI or CON --> CP(2)TT(2)). Rectal temperature was measured immediately before and after both the constant-paced sessions and 4-km timed trials. Cycling economy and Vo(2) were measured during the constant-paced sessions, and the average power output and completion times were recorded for each time trial.

RESULTS

Compared with control, rectal temperature was significantly lower (0.5 (0.4) degrees C) in cold-water immersion before CP(2) until the end of the second 4-km timed trial. However, the increase in rectal temperature (0.5 (0.2) degrees C) during CP(2) was not significantly different between conditions. During the second 4-km timed trial, power output was significantly greater in cold-water immersion (327.9 (55.7) W) compared with control (288.0 (58.8) W), leading to a faster completion time in cold-water immersion (6.1 (0.3) min) compared with control (6.4 (0.5) min). Economy and Vo(2) were not influenced by the cold-water immersion recovery intervention.

CONCLUSION

5-min cold-water immersion recovery significantly lowered rectal temperature and maintained endurance performance during subsequent high-intensity exercise. These data indicate that repeated exercise performance in heat may be improved when a short period of cold-water immersion is applied during the recovery period.

Predicting intermittent running performance: critical velocity versus endurance index

The aim of the present study was to examine the ability of the critical velocity (CV) and the endurance index (EI) to assess endurance performance during intermittent exercise. Thirteen subjects performed two intermittent runs: 15-s runs intersected with 15 s of passive recovery (15/15) and 30-s runs with 30-s rest (30/30). Runs were performed until exhaustion at three intensities (100, 95 and 90 % of the speed reached at the end of the 30 - 15 intermittent fitness test, V (IFT)) to calculate i) CV from the slope of the linear relationship between the total covered distance and exhaustion time (ET) (iCV); ii) anaerobic distance capacity from the Y-intercept of the distance/duration relationship (iADC); and iii) EI from the relationship between the fraction of V (IFT) at which the runs were performed and the log-transformed ET (iEI). Anaerobic capacity was indirectly assessed by the final velocity achieved during the Maximal Anaerobic Running Test (VMART). ET was longer for 15/15 than for 30/30 runs at similar intensities. iCV (15/15) and iCV (30/30) were not influenced by changes in ET and were highly dependent on V (IFT). Neither iADC (15/15) nor iADC (30/30) were related to VMART. In contrast, iEI (15/15) was higher than iEI (30/30), and corresponded with the higher ET. In conclusion, only iEI estimated endurance capacity during repeated intermittent running.

Attenuation of muscle damage by preconditioning with muscle hyperthermia 1-day prior to eccentric exercise

This study investigated the hypothesis that muscle damage would be attenuated in muscles subjected to passive hyperthermia 1 day prior to exercise. Fifteen male students performed 24 maximal eccentric actions of the elbow flexors with one arm; the opposite arm performed the same exercise 2-4 weeks later. The elbow flexors of one arm received a microwave diathermy treatment that increased muscle temperature to over 40 degrees C, 16-20 h prior to the exercise. The contralateral arm acted as an untreated control. Maximal voluntary isometric contraction strength (MVC), range of motion (ROM), upper arm circumference, muscle soreness, plasma creatine kinase activity and myoglobin concentration were measured 1 day prior to exercise, immediately before and after exercise, and daily for 4 days following exercise. Changes in the criterion measures were compared between conditions (treatment vs. control) using a two-way repeated measures ANOVA with a significance level of P < 0.05. All measures changed significantly following exercise, but the treatment arm showed a significantly faster recovery of MVC, a smaller change in ROM, and less muscle soreness compared with the control arm. However, the protective effect conferred by the diathermy treatment was significantly less effective compared with that seen in the second bout performed 4-6 weeks after the initial bout by a subgroup of the subjects (n = 11) using the control arm. These results suggest that passive hyperthermia treatment 1 day prior to eccentric exercise-induced muscle damage has a prophylactic effect, but the effect is not as strong as the repeated bout effect.

Core temperature and hydration status during an Ironman triathlon

BACKGROUND

Numerous laboratory based studies have documented that aggressive hydration strategies (approximately 1-2 litres/h) are required to minimise a rise in core temperature and minimise the deleterious effects of hyperthermia on performance. However, field data on the relations between hydration level, core body temperature, and performance are rare.

OBJECTIVE

To measure core temperature (Tcore) in triathletes during a 226 km Ironman triathlon, and to compare Tcore with markers of hydration status after the event.

METHOD

Before and immediately after the 2004 Ironman Western Australia event (mean (SD) ambient temperature 23.3 (1.9) degrees C (range 19-26 degrees C) and 60 (14)% relative humidity (44-87%)) body mass, plasma concentrations of sodium ([Na+]), potassium ([K+]), and chloride ([Cl-]), and urine specific gravity were measured in 10 well trained triathletes. Tcore was measured intermittently during the event using an ingestible pill telemetry system, and heart rate was measured throughout.

RESULTS

Mean (SD) performance time in the Ironman triathlon was 611 (49) minutes; heart rate was 143 (9) beats/min (83 (6)% of maximum) and Tcore was 38.1 (0.3) degrees C. Body mass significantly declined during the race by 2.3 (1.2) kg (-3.0 (1.5)%; p < 0.05), whereas urine specific gravity significantly increased (1.011 (0.005) to 1.0170 (0.008) g/ml; p < 0.05) and plasma [Na+], [K+], and [Cl-] did not change. Changes in body mass were not related to finishing Tcore (r = -0.16), plasma [Na+] (r = 0.31), or urine specific gravity (r = -0.37).

CONCLUSION

In contrast with previous laboratory based studies examining the influence of hypohydration on performance, a body mass loss of up to 3% was found to be tolerated by well trained triathletes during an Ironman competition in warm conditions without any evidence of thermoregulatory failure.

Reproducibility of a laboratory-based 40-km cycle time-trial on a stationary wind-trainer in highly trained cyclists

The purpose of the present study was to examine the reproducibility of laboratory-based 40-km cycle time-trial performance on a stationary wind-trainer. Each week, for three consecutive weeks, and on different days, forty-three highly trained male cyclists (x +/- SD; age = 25 +/- 6 y; mass = 75 +/- 7 kg; peak oxygen uptake [VO (2)peak] = 64.8 +/- 5.2 ml x kg (-1) x min (-1)) performed: 1) a VO (2)peak test, and 2) a 40-km time-trial on their own racing bicycle mounted to a stationary wind-trainer (Cateye - Cyclosimulator). Data from all tests were compared using a one-way analysis of variance. Performance on the second and third 40-km time-trials were highly related (r = 0.96; p < 0.001), not significantly different (57 : 21 +/- 2 : 57 vs. 57 : 12 +/- 3 : 14 min:s), and displayed a low coefficient of variation (CV) = 0.9 +/- 0.7 %. Although the first 40-km time-trial (58 : 43 +/- 3 : 17 min:s) was not significantly different from the second and third tests (p = 0.06), inclusion of the first test in the assessment of reliability increased within-subject CV to 3.0 +/- 2.9 %. 40-km time-trial speed (km x h (-1)) was significantly (p < 0.001) related to peak power output (W; r = 0.75), VO (2)peak (l x min (-1); r = 0.53), and the second ventilatory turnpoint (l x min (-1); r = 0.68) measured during the progressive exercise tests. These data demonstrate that the assessment of 40-km cycle time-trial performance in well-trained endurance cyclists on a stationary wind-trainer is reproducible, provided the athletes perform a familiarization trial.

Physiological responses to repeated bouts of high-intensity ultraendurance cycling--a field study case report

The present study aimed to 1) examine the relationship between laboratory-based measures and high-intensity ultraendurance (HIU) performance during an intermittent 24-h relay ultraendurance mountain bike race (approximately 20 min cycling, approximately 60 min recovery), and 2) examine physiological and performance based changes throughout the HIU event. Prior to the HIU event, four highly-trained male cyclists (age = 24.0 +/- 2.1 yr; mass = 75.0 +/- 2.7 kg; VO2peak = 70 +/- 3 ml x kg(-1) x min(-1)) performed 1) a progressive exercise test to determine peak volume of oxygen uptake (VO2peak), peak power output (PPO), and ventilatory threshold (T(vent)), 2) time-to-fatigue tests at 100% (TF100) and 150% of PPO (TF150), and 3) a laboratory simulated 40-km time trial (TT40). Blood lactate (Lac(-)), haematocrit and haemoglobin were measured at 6-h intervals throughout the HIU event, while heart rate (HR) was recorded continuously. Intermittent HIU performance, performance HR, recovery HR, and Lac(-) declined (P < 0.05), while plasma volume expanded (P < 0.05) during the HIU event. TF100 was related to the decline in lap time (r = -0.96; P < 0.05), and a trend (P = 0.081) was found between TF150 and average intermittent HIU speed (r = 0.92). However, other measures (VO2peak, PPO, T(vent), and TT40) were not related to HIU performance. Measures of high-intensity endurance performance (TF100, TF150) were better predictors of intermittent HIU performance than traditional laboratory-based measures of aerobic capacity.

Factors affecting performance in an ultraendurance triathlon

In the recent past, researchers have found many key physiological variables that correlate highly with endurance performance. These include maximal oxygen uptake (VO2max), anaerobic threshold (AT), economy of motion and the fractional utilisation of oxygen uptake (VO2). However, beyond typical endurance events such as the marathon, termed 'ultraendurance' (i.e. >4 hours), performance becomes harder to predict. The ultraendurance triathlon (UET) is a 3-sport event consisting of a 3.8 km swim and a 180 km cycle, followed by a 42.2 km marathon run. It has been hypothesised that these triathletes ride at approximately their ventilatory threshold (Tvent) during the UET cycling phase. However, laboratory assessments of cycling time to exhaustion at a subject's AT peak at 255 minutes. This suggests that the AT is too great an intensity to be maintained during a UET, and that other factors cause detriments in prolonged performance. Potential defeating factors include the provision of fuels and fluids due to finite gastric emptying rates causing changes in substrate utilisation, as well as fluid and electrolyte imbalances. Thus, an optimum ultraendurance intensity that may be relative to the AT intensity is needed to establish ultraendurance intensity guidelines. This optimal UET intensity could be referred to as the ultraendurance threshold.

The effects of 3000-m swimming on subsequent 3-h cycling performance: implications for ultraendurance triathletes

The purpose of this study was to examine the physiological effects of 3000-m swimming on subsequent 3-h cycling time trial performance in ultraendurance triathletes. Eight highly trained ultraendurance triathletes [mean (SEM) age 34 (2) years, body fat 12.5 (0.8)%, maximum oxygen consumption 63.2 (2.1) ml x kg(-1) x min(-1)] completed two randomly assigned trials 1 week apart. The swim/bike trial (SB) involved 3000 m of swimming [min:s 52:28 (1:48)] immediately followed by a 3-h cycling performance at a self-selected time-trial pace. The control trial (CON) consisted of an identical 3-h cycling time trial but without prior swimming. Subjects consumed an 8% carbohydrate (CHO)/electrolyte beverage during both trials at the rate of 60 g CHO x h(-1) and 1 l x h(-1). No significant differences were evident between CON and SB on the dependent measures (CON vs. SB): power output [W, 222 (14) W vs. 212 (13) W], heart rate [fc, 147 (5) beats x min(-1) vs. 143 (4) beats min(-1); %fcmax 80.0 (1.6)% vs. 78.4 (1.5)%], oxygen uptake [3.10 (0.12) l x min(-1) vs. 2.97 (0.15) l x min(-1)], minute ventilation [82.5 (4.4) l x min(-1) vs. 77.3 (3.7) l x min(-1)], rating of perceived exertion [14.6 (0.4) vs. 14.0 (0.1)], blood lactate [6.1 (0.5) mmol x l(-1) vs. 4.8 (0.5) mmol x l(-1)], and blood glucose [5.0 (0.2) mmol x l(-1) vs. 5.3 (0.1) mmol x l(-1); all non-significant at the P>0.05 level]. However, the CON respiratory exchange ratio was significantly greater than for SB [0.91 (0.01) vs. 0.89 (0.01); P<0.05], suggesting that the SB trial required a greater reliance on lipid as a fuel substrate. Hence, the main finding in the present study was that 3000 m of swimming had no significant performance effect (in terms of W) on subsequent 3-h cycling performance in ultraendurance triathletes.