Francesco Marino

Methods, advantages, and limitations of body cooling for exercise performance

Precooling studies confirm that increasing body heat is a limiting factor during exercise. However, it seems that precooling is only beneficial for endurance exercise of up to 30–40 minutes rather than intermittent or short duration exercise.

Relationships between isokinetic knee strength, single-sprint performance, and repeated-sprint ability in football players.

Previous research has demonstrated that muscular strength of the knee extensors is related to the speed an athlete can produce during a single-sprint performance. Football players, as well as many other athletes on the field and the court, execute multiple sprints during the course of a match. The purpose of this study was to examine the relationships between leg strength, single-sprint speed, and repeated-sprint ability. Thirty-eight football players from 3 codes (soccer, rugby league, rugby union) completed a 12- × 20- m repeated-sprint protocol and were evaluated for peak isokinetic knee extension and flexion torque at 608·s−1, 1508·s−1, and 2408·s−1. Although single-sprint performance correlated with peak extensor and flexor torque at all velocities, the strongest correlation was observed between relative knee extensor torque at 2408·s−1 and the initial acceleration phase (0–10 m) of the single-sprint performance (r 520.714, p < 0.01). However, the data suggest that factors other than strength contribute to repeated-sprint ability. This finding provides new evidence in elucidating the relationship between strength and repeated-sprint performance.

Exercise heat stress does not reduce central activation to non-exercised human skeletal muscle

In this study we measured the central activation ratio (CAR) of the leg extensors and the elbow flexor muscles before and after exhaustive exercise in the heat to determine whether exercise‐induced hyperthermia affects the CNS drive to exercised (leg extensors) and/or non‐exercised (forearm flexors) muscle groups. Thirteen subjects exercised at fixed intensities representative of a percentage of peak power output (PPO) for 10 min periods (50%, 40%, 60%, 50%) and then at 75% PPO until exhaustion in ambient conditions of 39.3 ± 0.8 °C and 60.0 ± 0.8% relative humidity. Before and immediately following exercise subjects performed a series of maximal voluntary contractions (MVCs) with the leg extensors (exercised muscles) and forearm flexors (non‐exercised muscles). The degree of voluntary activation during the sustained MVCs was assessed by superimposing electrical stimulation to the femoral nerve and the biceps brachii. Exercise to exhaustion increased the rectal temperature from 37.2 ± 0.2 to 38.8 ± 0.2 °C (P < 0.0001). The mean heart rate at the end of exercise to exhaustion was 192 ± 3 beats min−1. Leg extensor voluntary force was significantly reduced from 595 ± 143 to 509 ± 105 N following exercise‐induced hyperthermia but forearm flexor force was similar before and after exercise. The CAR of the leg extensors decreased from 94.2 ± 1.3% before exercise to 91.7 ± 1.5% (P < 0.02) following exercise‐induced hyperthermia. However, the CAR for the forearm flexors remained at similar levels before and after exercise. The data suggest that the central nervous system selectively reduces central activation to specific skeletal muscles as a consequence of exercise‐induced hyperthermia.

Glycerol hyperhydration fails to improve endurance performance and thermoregulation in humans in a warm humid environment

It is equivocal whether glycerol hyperhydration improves exercise performance and thermoregulation in the heat. The purpose of this study was to compare the effectiveness of glycerol with water hyperhydration, using a reliable, self-paced variable-intensity cycling protocol under hot, humid conditions. Seven moderately-to-well trained subjects ingested either a solution consisting of 1.2 g kg−1 body mass (BM) glycerol mixed with 21xa0ml kg−1 BM flavoured water (GLY) or placebo (PL), which was flavoured water of equal volume to the GLY trial, 2.5xa0h before exercise. Following hyperhydration, subjects undertook a self-paced, variable-intensity cycling protocol designed to simulate racing, with the aim being to cycle as great a distance as possible over 60xa0min. There were no differences in total distance cycled between conditions (29.7±5.7xa0km for PL, 28.9±5.7xa0km for GLY). Power output was not different at any time between conditions. Terminal rectal temperatures were 39.0±0.5xa0°C for PL and 38.8±0.7xa0°C for GLY and were not significantly different. Heart rate was significantly higher for GLY only during the high-intensity efforts. The sweat rate for GLY was 1.72±0.28 l h−1 (P<0.01) compared with 1.15±0.29 l h−1 for PL. It is concluded that glycerol hyperhydration has no significant advantage over water hyperhydration on performance or thermoregulation during a 1-h, variable-intensity exercise performance.

Cerebral oxygenation decreases but does not impair performance during self-paced, strenuous exercise

Aim:u2002 The reduction in cerebral oxygenation (Cox) is associated with the cessation of exercise during constant work rate and incremental tests to exhaustion. Yet in exercises of this nature, ecological validity is limited due to work rate being either fully or partly dictated by the protocol, and it is unknown whether cerebral deoxygenation also occurs during self‐paced exercise. Here, we investigated the cerebral haemodynamics during a 5‐km running time trial in trained runners.

Effect of deception of distance on prolonged cycling performance.

This study examined the effect of deception of distance end-point on prolonged cycling performance. 21 subjects were randomly allocated to three groups (n = 7 per group). Each group completed three self-paced time-trials separated by one day. Subjects were told that each trial was a 30-km time-trial and were required to complete the distance in the fastest time possible. Following the initial trial of 30 km, one group completed Trial 2 with a longer distance (long distance group; 36 km), another group with a shorter distance (24 km; short distance group), and the third group as control (30 km; control). Each group then completed a third time-trial of 30 km. At no time was the deception of distance in Trial 2 disclosed to the subjects, and all sources of physiological and mechanical feedback were withheld during the trials. Data from Trials 1 and 3 were analysed by repeated-measures analysis of covariance. Time to complete Trial 1 was similar among groups (–65 min.). Following the deception in Trial 2 the time to complete the 30 km in Trial 3 was increased for the short distance group, decreased for the long distance group, whilst the time for the control group remained unchanged. The times to complete the 30 km on Trials 1 and 3 were matched by changes in power output throughout the trials. It is concluded that subjects deceived of the actual distance completed will complete the subsequent performance trial based on perceived effort rather than on actual distance.

Whole-body pre-cooling does not alter human muscle metabolism during sub-maximal exercise in the heat.

Abstract. Muscle metabolism was investigated in seven men during two 35xa0min cycling trials at 60% peak oxygen uptake, at 35°C and 50% relative humidity. On one occasion, exercise was preceded by whole-body cooling achieved by immersion in water during a reduction in temperature from 29 to 24°C, and, for the other trial, by immersion in water at a thermoneutral temperature (control, 34.8°C). Pre-cooling did not alter oxygen uptake during exercise (P>0.05), whilst the change in cardiac frequency and body mass both tended to be lower following pre-cooling (0.05< P<0.10). When averaged over the exercise period, muscle and oesophageal temperatures after pre-cooling were reduced by 1.5 and 0.6°C respectively, compared with control (P<0.05). Pre-cooling had a limited effect on muscle metabolism, with no differences between the two conditions in muscle glycogen, triglyceride, adenosine triphosphate, creatine phosphate, creatine or lactate contents at rest, or following exercise. These data indicate that whole-body pre-cooling does not alter muscle metabolism during submaximal exercise in the heat. It is more likely that thermoregulatory and cardiovascular strain are reduced, through lower muscle and core temperatures.

Early-phase neuromuscular adaptations to high- and low-volume resistance training in untrained young and older women

Abstract We compared early-phase effects between high- and low-volume moderate-intensity resistance training on lean muscle volume, maximal bilateral leg extension strength, maximal isometric torque, normalized maximal bilateral leg extension strength, normalized maximal isometric torque, and muscle recruitment of the right knee extensors in previously untrained young (23.8 ± 3.7 years, range 20–30 years; n = 16) and older women (67.6 ± 6.3 years, range 60–78 years; n = 15). Participants performed either one set or three sets of 10 repetitions for the bilateral leg extension and bilateral leg curl at an intensity of 50–75% of maximal strength 3 days per week for 10 weeks. Main effects were observed over time for all variables (P < 0.05) with increases ranging from 7.1% to 27.8% and effect sizes (Cohens d) ranging from 0.45 to 1.38. No interactions between age and training volume over time were observed for any variable (P > 0.05). Our results provide a novel contribution to the literature demonstrating that additional neuromuscular adaptation during early-phase moderate-intensity resistance training in previously untrained young and older women may not be elicited through higher-volume training when training loads are matched provided that a minimal volume threshold is attained. These findings may have practical applications for the prescription of short-duration resistance training programmes to enhance muscle strength and achieve hypertrophic and non-hypertrophic adaptations in untrained women.

Failure of fluid ingestion to improve self-paced exercise performance in moderate-to-warm humid environments

Abstract It has been previously proposed that fluid ingestion might enhance performance and thermoregulation through the heat storage capacity of the ingested fluid. While accurate under certain conditions, in some situations this cannot account for differences in thermoregulatory and performance responses. To test this hypothesis seven subjects performed a 60xa0min self-paced cycling time trial on four occasions, differentiated by ambient temperature (moderate 19.8±0.6°C, warm 33.2±0.2°C; 63.3±0.6% relative humidity) and fluid ingestion regime (no fluid, NF; or sufficient fluid, F, to prevent any change in body mass). No differences were observed for total distance cycled or final core temperature during exercise where for the moderate-NF, moderate-F, warm-NF and warm-F conditions were 32.6±6.4, 30.8±5.7, 30.5±4.8, 30.1±5.0xa0km and 38.9±0.3°C, 38.6±0.4°C, 38.9±0.5°C, 38.7±0.4°C, respectively. Furthermore, pacing strategy, as indicated by distance covered during maximal sprint and submaximal sections of the trial were similar among conditions. Although this result is not dissimilar to previous findings, the data show that complete fluid replacement during exercise of 1xa0h does not provide the proposed heat sink sufficient to attenuate thermoregulatory strain and improve performance over no fluid replacement. The findings indicate that the ingestion of fluids replacing 100% of sweat losses has no effect on 1xa0h of self-paced cycling performance or thermoregulation in moderate and warm conditions.

Cold water immersion recovery following intermittent-sprint exercise in the heat

This study examined the effects of cold water immersion (CWI) on recovery of neuromuscular function following simulated team-sport exercise in the heat. Ten male team-sport athletes performed two sessions of a 2xa0×xa030-min intermittent-sprint exercise (ISE) in 32°C and 52% humidity, followed by a 20-min CWI intervention or passive recovery (CONT) in a randomized, crossover design. The ISE involved a 15-m sprint every minute separated by bouts of hard running, jogging and walking. Voluntary and evoked neuromuscular function, ratings of perceived muscle soreness (MS) and blood markers for muscle damage were measured pre- and post-exercise, immediately post-recovery, 2-h and 24-h post-recovery. Measures of core temperature (Tcore), heart rate (HR), capillary blood and perceptions of exertion, thermal strain and thirst were also recorded at the aforementioned time points. Post-exercise maximal voluntary contraction (MVC) and activation (VA) were reduced in both conditions and remained below pre-exercise values for the 24-h recovery (Pxa0<xa00.05). Increased blood markers of muscle damage were observed post-exercise in both conditions and remained elevated for the 24-h recovery period (Pxa0<xa00.05). Comparative to CONT, the post-recovery rate of reduction in Tcore, HR and MS was enhanced with CWI whilst increasing MVC and VA (Pxa0<xa00.05). In contrast, 24-h post-recovery MVC and activation were significantly higher in CONT compared to CWI (Pxa0=xa00.05). Following exercise in the heat, CWI accelerated the reduction in thermal and cardiovascular load, and improved MVC alongside increased central activation immediately and 2-h post-recovery. However, despite improved acute recovery CWI resulted in an attenuated MVC 24-h post-recovery.