What the experts say
Nigel Hetherington reviews the latest research material relating to coaching, exercise physiology and athletic development.
A newly developed method for measuring passive length-tension relations of a single human muscle was used to quantify changes in the mechanical properties of the gastrocnemius after eccentric exercise.
Twelve subjects performed eccentric exercise on the right leg for 1 h by walking backwards downhill on a treadmill. Passive ankle torque was measured as the ankle was rotated within its available range, with the knee in eight different angles. Subjects were studied before exercise, 1 h after exercise, and 24 h later, with further measurements at 48 h and at 1 wk in a subset of six subjects. Subjects also rated the level of perceived muscle soreness on a 10-point scale during walking on flat ground. Researchers examined passive tension in the gastrocnemius at a standard length before and at various times after exercise.
Muscle tension increased significantly at this length 1 h after exercise (34.7 +/- 7.3%), peaked at 24 h (88.4 +/- 12.6%), declined at 48 h (45.5 +/- 4.4%), and returned to the control level at 1 wk. The stiffness of the gastrocnemius in the sitting and standing postures (i.e. at short and long lengths) was derived from passive length-tension relations. Stiffness increased after exercise, and the relative changes in muscle stiffness were similar in both positions. There was no apparent correlation between stiffness and subjective reports of muscle soreness during walking.This study provides the first specific measurements of the increase in stiffness of the human gastrocnemius in vivo after a single bout of eccentric exercise. The increase peaks at 24 h and is nearly fully resolved within 1 wk.
A study investigated the thermal strain of active recovery (AR) versus passive recovery (PR) during prolonged, intermittent-sprint exercise characteristic of team sports.
Eight men performed two intermittent-sprint tests in the heat (35C, 44% relative humidity (RH)), with either AR or PR.
No differences were found between conditions for mean work or power per sprint. AR was associated with a significantly higher heart rate (HR), temperature measures for muscle (Tmu), rectal (Tre), body (Tb), and skin (Tsk) after 7, 10, and 25 min, respectively. Body heat storage and heat-strain measures were significantly higher in AR compared with PR. The differences in Tmu and thermoregulatory strain between AR and PR were greater than the differences in Tre and Tb.These results are attributed to a greater rate of whole-body heat loss during the AR protocol. Because AR has previously been associated with a greater muscle pump, a greater blood flow to surface veins and inactive musculature may have been maintained, allowing greater heat dissipation than during PR, when blood was likely to be pooling in the legs. Despite the greater increase in body temperature and heat strain in AR than in PR, there was no difference in performance, possibly because critical temperature levels were not reached in this study.
Repeated short-term exposures to severe hypoxia, alternated with similar intervals of normoxia, are recommended for performance enhancement in sports. However, scientific evidence for the efficiency of this method is controversial with regard to anaerobic performance. A study was carried out to investigate the effects on both anaerobic and aerobic performance.
During 15 consecutive days, 20 endurance-trained men (VO2 max ~ 60 mLkg-1min-1) were exposed each day to breathing either a gas mixture (11% O2 on days 1-7 and 10% O2 on days 8-15; hypoxia group) or compressed air (control), six times for 6 min, followed by 4 min of breathing room air for a total of six consecutive cycles. Before and after the treatment, an incremental cycle ergometer test to exhaustion and the Wingate anaerobic test were performed.
Hypoxic treatment did not improve peak power or mean power during the Wingate anaerobic test, nor did it affect maximal oxygen uptake (VO2 max), maximal power output (Pmax), lactate threshold or levels of heart rate (HR), minute ventilation (VE), oxygen uptake (VO2), or blood lactate concentration at the submaximal workloads during the ergometer test. Maximal lactate concentration after the tests and HRmax and maximal respiratory exchange ratio during the ergometer test were not significantly different between groups at any time.
The results of this study demonstrated that 1 h of intermittent hypoxic exposure for 15 consecutive days has no effect on aerobic or anaerobic performance.
Twelve male subjects cycled for 2.0 h at 64% Wmax and 73% VO2 peak with 3-min rest intervals interspersed every 10 min (2.6 h of total exercise time, including rest intervals) with placebo (P) or carbohydrate (C) beverages. RPE was assessed during the last minute of each 10-min exercise interval and then every 30 s during the 3-min recovery period.
The pattern of change in RPE over time was significantly different between C and P ingestion, with attenuated RPE responses found for both overall body (O) and legs (L). A significant main effect was found for recovery RPE-O between C and P ingestion, with attenuated RPE responses found in the later part of the 2-h run. C was associated with higher respiratory exchange ratios and plasma levels of glucose and with lower levels of plasma cortisol.
These data indicate that carbohydrate supplementation attenuates perceived exertion during prolonged intermittent exercise and recovery.
A review study investigated the precise effect of plyometric training (PT) on vertical jump height in healthy individuals. Statistical analysis of randomised and non-randomised controlled trials that evaluated the effect of PT on four typical vertical jump height tests was carried out: squat jump (SJ); countermovement jump (CMJ); countermovement jumps with the arm swing (CMJA); and drop jump (DJ). Published data on changes in jump height for the plyometric and control groups were evaluated separately for each type of jump. A total of 26 studies yielding 13 data points for SJ, 19 for CMJ, 14 for CMJA and 7 for DJ met the initial inclusion criteria. The pooled estimate of the effect of PT on vertical jump height was 4.7%, 8.7%, 7.5% and 4.7% for the SJ, CMJ, CMJA and DJ, respectively. PT provides a statistically significant and relevant improvement in vertical jump height. These results justify the application of PT for the purpose of development of vertical jump performance in healthy individuals.
The effects of different preparation procedures (warm-up (WU), pre-cooling (PC), control (C)) on endurance performance in the heat were investigated.
20 male subjects completed three treadmill runs to exhaustion (5 days apart). In each session, all subjects performed an incremental running test after WU (20 min at 70% maximum heart rate (HR)), after PC (wearing a cooling vest (0°C–5°C) for 20 min at rest) or without particular preparation (C). After a 5-min break, the exercise protocol commenced at a workload of 9 km/h and was increased by 1 km/h every 5 min until the point of volitional fatigue.
In the PC condition, the running performance (~32.5 min; mean) was significantly higher than in WU (~26.9 min) and in C conditions (~30.3 min). During the first 30 min of testing, HR, tympanic temperature and skin temperature were significantly lower after PC than after WU. There were no significant differences in lactate concentration; however, there was a trend to lower values after WU.The use of an ice-cooling vest for 20 min before exercising improved running performance, whereas the 20 min WU procedure had a distinctly detrimental effect. Cooling procedures including additional parts of the body such as the head and the neck might further enhance the effectiveness of PC measures.
40 untrained volunteers performed an eccentric loading protocol with their non-dominant leg and were randomised to three 1-min immersions in either ice water (5±1°C) or tepid water (24°C).
Pain and tenderness, swelling (thigh circumference), function (one-legged hop for distance), maximal isometric strength and serum creatine kinase (CK) were recorded at baseline, 24, 48 and 72 h after exercise.
No significant differences were observed between groups with regard to changes in most pain parameters, tenderness, isometric strength, swelling, hop-for-distance or serum CK over time. There was a significant difference in pain on sit-to-stand at 24 h, with the intervention group demonstrating a greater increase in pain than the control group. The protocol of ice-water immersion used in this study was ineffectual in minimising markers of DOMS in untrained individuals. This study challenges the wide use of this intervention as a recovery strategy by athletes.
Ankle sprains are frequent injuries in soccer. Several strategies were studied to prevent further ankle sprains in athletes: the most common are proprioceptive training, strength training, and orthoses.
Eighty male soccer players who had experienced previous ankle inversion sprain were randomly selected. The subjects were individually and randomly assigned to 4 study groups. Data on the frequency of ankle sprain re-injury were collected at the end of the session.
The incidence of ankle sprains in players in the proprioception training group was significantly lower than in the control group. Neither the strength nor orthotic groups improved in comparison with the control group.
Proprioceptive training, compared with no intervention, was an effective strategy to reduce the rate of ankle sprains among male soccer players who suffered an ankle sprain.
Achilles tendinopathy is a common overuse injury, especially among athletes involved in running and jumping. Often an initial period of rest is recommended. A study evaluated if continued running and jumping during treatment with an Achilles tendon-loading strengthening program has an effect on the outcome.
Subjects were randomly allocated to 2 different treatment groups. The exercise training group (n = 19) was allowed, with the use of a pain-monitoring model, to continue Achilles tendon-loading activity, such as running and jumping, whereas the active rest group (n = 19) had to stop such activities during the first 6 weeks. All patients were rehabilitated according to an identical rehabilitation program. No significant differences in the rate of improvements were found between the two groups. Both groups showed, however, significant improvements, compared with baseline on the primary outcome measure at all the evaluations.
No negative effects could be demonstrated from continuing Achilles tendon-loading activity, such as running and jumping, with the use of a pain-monitoring model, during treatment. A training regimen of continued, pain-monitored, tendon-loading physical activity might, therefore, represent a valuable option for patients with Achilles tendinopathy.
A study investigated the effect of acute resistance exercise (RE) on lipolysis within adipose tissue and hence body composition. Lipolysis and blood flow were measured in abdominal subcutaneous adipose tissue via microdialysis before, during, and for 5 h following whole body RE as well as on a non-exercise control day (C) in eight young (24 ± 0.7 yr), active (>3 RE session/wk for at least 2 yr) male participants. The mechanism behind RE contributing to improved body composition was found to be in part due to enhanced abdominal subcutaneous adipose tissue lipolysis and improved whole-body fat oxidation and energy expenditure in response to RE.
The effects of prior moderate- and prior heavy-intensity exercise on the subsequent metabolic response to incremental exercise were examined. Healthy, young adult subjects (n = 8) performed three randomized plantar-flexion exercise tests: 1) an incremental exercise test (0.6 W/min) to volitional fatigue; 2) Ramp preceded by 6 min of moderate-intensity, constant-load exercise below the intracellular pH threshold (pHT); and 3) Ramp preceded by 6 min of heavy-intensity, constant-load exercise above pHT; the constant-load and incremental exercise periods were separated by 6 min of rest. The findings were that prior heavy-intensity exercise delayed the onset of intracellular acidosis and enhanced exercise performance during a subsequent incremental exercise test.
The effects of the intensity and duration of exercise on training adaptations in a muscle of adolescent racehorses revealed some interesting evidence. Six pre-trained thoroughbreds performed six consecutive conditioning programs of varying lactate-guided intensities [velocities eliciting blood lactate concentrations of 2.5 mmol/l (v2.5) and 4 mmol/l (v4), respectively] and durations (5, 15, 25 min). Pre- and post-training gluteus muscle biopsies were analysed for a range of key markers. Although training adaptations were similar in nature, they varied in magnitude among the different training protocols. Overall, the use of v4 as the exercise intensity for 25 min elicited the most consistent training adaptations in muscle, whereas the minimal training stimulus that evoked any significant change was identified with exercises of 15 min at v2.5. Within this range, muscular adaptations showed significant trends to be proportional to the exercise load of specific training programs. Taken together, these data suggest that muscular adaptations to training in horses occur on a continuum that is based on the exercise intensity and duration of training. The practical implications of this study are that exercises for 15 to 25 min/day at velocities between v2.5 and v4 can improve in the short term (3 wk) the muscular stamina in thoroughbreds. However, exercises of 5–15 min at v4 are necessary to enhance muscular features related to strength (hypertrophy).
Any human volunteers for a follow-up study?
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About the Author
Nigel Hetherington was the Head Track & Field Coach at the internationally acclaimed Singapore Sports School. He is a former National Performance Development Manager for Scottish Athletics and National Sprints Coach for Wales. Qualified and highly active as a British Athletics level 4 performance coach in all events he has coached athletes to National and International honours in sprints, hurdles as well as a World Record holder in the Paralympic shot. He has 10 years' experience as senior coach educator and assessor trainer on behalf of British Athletics. Nigel is also an experienced athlete in sprint (World Masters Championship level) and endurance (3-hour marathon runner plus completed the 24 hour 'Bob Graham Round' ultra-endurance event up and down 42 mountain peaks in the English Lake District). He is a chartered chemist with 26 years' experience in scientific research and publishing.
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