Carmel Goodman

Physiological and Metabolic Responses of Repeated-Sprint Activities Specific to Field-Based Team Sports

Field-based team sports, such as soccer, rugby and hockey are popular worldwide. There have been many studies that have investigated the physiology of these sports, especially soccer. However, some fitness components of these field-based team sports are poorly understood. In particular, repeated-sprint ability (RSA) is one area that has received relatively little research attention until recent times. Historically, it has been difficult to investigate the nature of RSA, because of the unpredictability of player movements performed during field-based team sports. However, with improvements in technology, time-motion analysis has allowed researchers to document the detailed movement patterns of team-sport athletes. Studies that have published time-motion analysis during competition, in general, have reported the mean distance and duration of sprints during field-based team sports to be between 10–20m and 2–3 seconds, respectively. Unfortunately, the vast majority of these studies have not reported the specific movement patterns of RSA, which is proposed as an important fitness component of team sports. Furthermore, there have been few studies that have investigated the physiological requirements of one-off, short-duration sprinting and repeated sprints (≪10 seconds duration) that is specific to field-based team sports. This review examines the limited data concerning the metabolic changes occurring during this type of exercise, such as energy system contribution, adenosine triphosphate depletion and resynthesis, phosphocreatine degradation and resynthesis, glycolysis and glycogenolysis, and purine nucleotide loss. Assessment of RSA, as a training and research tool, is also discussed.

The effect of combined aerobic and resistance exercise training on vascular function in Type 2 diabetes

OBJECTIVES The purpose of this study was to examine whether exercise training stimulates a generalized improvement in vascular function in patients with type 2 diabetes mellitus. BACKGROUND Exercise is often recommended for patients with type 2 diabetes to improve physical conditioning and glycemic control. This study examined the effect of eight weeks of exercise training on conduit and resistance vessel function in patients with type 2 diabetes, using a randomized crossover design. METHODS Both resistance vessel endothelium-dependent and -independent functions were determined by forearm plethysmography and intrabrachial infusions of acetylcholine (ACh) and sodium nitroprusside (SNP), respectively, in 16 patients with type 2 diabetes. Conduit vessel endothelial function was assessed in 15 of these patients using high-resolution ultrasound and flow-mediated dilation of the brachial artery; glyceryl trinitrate (GTN) was used as an endothelium-independent dilator. RESULTS Flow-mediated dilation increased from 1.7 +/- 0.5% to 5.0 +/- 0.4% following training (p < 0.001). The forearm blood flow ratio to ACh was significantly improved (analysis of variance, p < 0.05). Responses to SNP and GTN were unchanged. Endothelium-dependent vasodilation was enhanced in both conduit and resistance vessels. CONCLUSIONS If endothelial dysfunction is an integral component of the pathogenesis of vascular disease, as currently believed, this study supports the value of an exercise program in the management of type 2 diabetes.

Time–motion analysis of elite field hockey, with special reference to repeated-sprint activity

Limited information exists about the movement patterns of field-hockey players, especially during elite competition. Time–motion analysis was used to document the movement patterns during an international field-hockey game. In addition, the movement patterns of repeated-sprint activity were investigated, as repeated-sprint ability is considered to be an important fitness component of team-sport performance. Fourteen members of the Australian mens field-hockey team (age 26±3 years, body mass 76.7±5.6 kg, [Vdot]O2max 57.9±3.6 ml · kg−1 · min−1; mean±s) were filmed during an international game and their movement patterns were analysed. The majority of the total player game time was spent in the low-intensity motions of walking, jogging and standing (46.5±8.1, 40.5±7.0 and 7.4±0.9%, respectively). In comparison, the proportions of time spent in striding and sprinting were 4.1±1.1 and 1.5±0.6%, respectively. Our criteria for ‘repeated-sprint’ activity (defined as a minimum of three sprints, with mean recovery duration between sprints of less than 21 s) was met on 17 occasions during the game (total for all players), with a mean 4±1 sprints per bout. On average, 95% of the recovery during the repeated-sprint bouts was of an active nature. In summary, the results suggest that the motion activities of an elite field-hockey competition are similar to those of elite soccer, rugby and Australian Rules football. In addition, the investigation of repeated-sprint activity during competition has provided additional information about the unique physiological demands of elite field-hockey performance.

Combined aerobic and resistance exercise improves glycemic control and fitness in type 2 diabetes

We investigated the effect of an 8 week circuit training (CT) program, combining aerobic and resistance exercise, on indices of glycemic control, cardiorespiratory fitness, muscular strength and body composition in 16 subjects (age 52 +/- 2 years) with type 2 diabetes using a prospective randomised crossover protocol. Submaximal exercise heart rate and rate pressure product were significantly lower after training (P<0.05), whilst ventilatory threshold increased (11.8 +/- 0.7 vs 13.8 +/- 0.6 ml kg(-1)min(-1), P<0.001). Muscular strength also increased with training (403 +/- 30 to 456 +/- 31 kg, P<0.001), whilst skinfolds (148.7 +/- 11.5 vs 141.1 +/- 10.7 mm, P<0.05), % body fat (29.5 +/- 1.0 vs 28.7 +/- 1.1%, P<0.05) and waist:hip ratio (99.2 +/- 1.5 vs 97.9 +/- 1.4%, P<0.05) significantly decreased. Concurrently, peak oxygen uptake (P<0.05) and exercise test duration (P<0.001) increased following training, whilst glycated hemoglobin (P<0.05) and fasting blood glucose (P<0.05) decreased. CT is an effective method of training that improved functional capacity, lean body mass, strength and glycemic control in subjects with type 2 diabetes.

Athletic induced iron deficiency: new insights into the role of inflammation, cytokines and hormones

Iron is utilised by the body for oxygen transport and energy production, and is therefore essential to athletic performance. Commonly, athletes are diagnosed as iron deficient, however, contrasting evidence exists as to the severity of deficiency and the effect on performance. Iron losses can result from a host of mechanisms during exercise such as hemolysis, hematuria, sweating and gastrointestinal bleeding. Additionally, recent research investigating the anemia of inflammation during states of chronic disease has allowed us to draw some comparisons between unhealthy populations and athletes. The acute-phase response is a well-recognised reaction to both exercise and disease. Elevated cytokine levels from such a response have been shown to increase the liver production of the hormone Hepcidin. Hepcidin up-regulation has a negative impact on the iron transport and absorption channels within the body, and may explain a potential new mechanism behind iron deficiency in athletes. This review will attempt to explore the current literature that exits in this new area of iron metabolism and exercise.

Changes in performance muscle metabolites, enzymes and fibre types after short sprint training

Abstract In contrast to endurance training, little research has been carried out to investigate the effects of short (<10 s) sprint training on performance, muscle metabolism and fibre types. Nine fit male subjects performed a mean of 16 outdoor sprint running training sessions over 6 weeks. Distances sprinted were 30–80 m at 90–100% maximum speed and between 20 and 40 sprints were performed in each session. Endurance (maximal oxygen consumption; V˙O2max), sprint (10 m and 40 m times), sustained sprint (supramaximal treadmill run) and repeated sprint (6 × 40 m sprints, 24 s recovery between each) performance tests were performed before and after training. Muscle biopsy samples (vastus lateralis) were also taken to examine changes in metabolites, enzyme activities and fibre types. After training, significant improvements were seen in 40 m time (P < 0.01), supramaximal treadmill run time (P < 0.05), repeated sprint performance (P < 0.05) and V˙O2max (P < 0.01). Resting muscle concentrations of ATP and phosphocreatine did not change. Phosphorylase activity increased (P < 0.025), citrate synthase activity decreased (P < 0.01), but no significant changes were recorded in myokinase and phosphofructokinase activities. The proportion of type II muscle fibres increased significantly (P < 0.05). These results demonstrate that 6 weeks of short sprint training can improve endurance, sprint and repeated sprint ability in fit subjects. Increases in the proportion of type II muscle fibres are also possible with this type of training.

Effect of water immersion methods on post-exercise recovery from simulated team sport exercise

This study aimed to compare the efficacy of hot/cold contrast water immersion (CWI), cold-water immersion (COLD) and no recovery treatment (control) as post-exercise recovery methods following exhaustive simulated team sports exercise. Repeated sprint ability, strength, muscle soreness and inflammatory markers were measured across the 48-h post-exercise period. Eleven male team-sport athletes completed three 3-day testing trials, each separated by 2 weeks. On day 1, baseline measures of performance (10 m x 20 m sprints and isometric strength of quadriceps, hamstrings and hip flexors) were recorded. Participants then performed 80 min of simulated team sports exercise followed by a 20-m shuttle run test to exhaustion. Upon completion of the exercise, and 24h later, participants performed one of the post-exercise recovery procedures for 15 min. At 48 h post-exercise, the performance tests were repeated. Blood samples and muscle soreness ratings were taken before and immediately after post-exercise, and at 24h and 48 h post-exercise. In comparison to the control and CWI treatments, COLD resulted in significantly lower (p<0.05) muscle soreness ratings, as well as in reduced decrements to isometric leg extension and flexion strength in the 48-h post-exercise period. COLD also facilitated a more rapid return to baseline repeated sprint performances. The only benefit of CWI over control was a significant reduction in muscle soreness 24h post-exercise. This study demonstrated that COLD following exhaustive simulated team sports exercise offers greater recovery benefits than CWI or control treatments.

The Influence of Exercise-Induced Plasma Volume Changes on the Interpretation of Biochemical Parameters Used for Monitoring Exercise, Training and Sport

A number of studies have demonstrated considerable plasma volume changes during and after exposure to different environmental and physiological conditions. These changes are thought to result from transient fluid shifts into (haemodilution) and out of (haemoconcentration) the intravascular space. If the levels of plasma constituents are to be routinely measured for research purposes or used as indicators of training adaptation or the health of an athlete, then it is important to consider the dynamic nature of plasma volume.Controversy still exists over the relevance of plasma volume interactions with plasma constituent levels, and while some investigators have taken plasma volume shifts into account, others have chosen to ignore these changes. Bouts of acute exercise have been shown to produce a transient haemoconcentration immediately after long distance running, bicycle ergometry and both maximal and submaximal swimming exercise. While these changes are transient, lasting only a few hours, other studies have reported a longer term haemodilution following acute exercise. In addition, endurance training has been shown to cause long term expansion of the plasma volume.It would, therefore, seem important to consider the influence of plasma volume changes on plasma solutes routinely measured for research, and as markers of training adaptation, prior to arriving at conclusions and recommendations based purely on their measured plasma level. To further confound this issue, plasma volume changes are known to be associated with heat acclimatisation, hydration state, physical training and postural changes, all of which may differ from one experiment or exercise bout to the next, and should thus be taken into account.

Exercise training, vascular function, and functional capacity in middle-aged subjects

PURPOSE The aim of this study was to investigate the effect of 8 wk of exercise training on functional capacity, muscular strength, body composition, and vascular function in sedentary but healthy subjects by using a randomized, crossover protocol. METHODS After familiarization sessions, 19 subjects aged 47 +/- 2 yr (mean +/- SE) undertook a randomized, crossover design study of the effect of 8 wk of supervised circuit training consisting of combined aerobic and resistance exercise. Peak oxygen uptake (.VO(2peak)), sum of 7 maximal voluntary contractions and the sum of 8 skinfolds and 5 segment girths were determined at entry, crossover, and 16 wk. Endothelium-dependent and -independent vascular function were determined by forearm strain-gauge plethysmography and intrabrachial infusions of acetylcholine (ACh) and sodium nitroprusside (SNP) in 16 subjects. RESULTS Training did not alter ACh or SNP responses. .VO(2peak), (28.6 +/- 1.1 to 32.6 +/- 1.3 mL.kg(-1).min(-1), P < 0.001), exercise test duration (17.4 +/- 1.1 to 22.1 +/- 1.2 min, P < 0.001), and muscular strength (465 +/- 27 to 535 +/- 27 kg, P < 0.001) significantly increased after the exercise program, whereas skinfolds decreased (144 +/- 10 vs 134 +/- 9 mm, P < 0.001). CONCLUSION These results suggest that moderate intensity circuit training designed to minimize the involvement of the arms improves functional capacity, body composition, and strength in healthy, middle-aged subjects without significantly influencing upper limb vascular function. This finding contrasts with previous studies in subjects with type 2 diabetes and heart failure that employed an identical training program.

Muscle phosphocreatine repletion following single and repeated short sprint efforts

Phosphocreatine (PCr) repletion following either single (1x6 s, n=7) or repeated (5x6 s, departing every 30 s, n=8) maximal short sprint cycling efforts was measured in separate groups of trained subjects. Muscle biopsies (vastus lateralis) were taken pre‐exercise before warming up, and then at 10 s, 30 s and 3 min post‐exercise. After the 1 × 6 s sprint PCr concentration was respectively, 55% (10 s; P<0.01), 69% (30 s; P<0.01) and 90% (3 min; NS) of the pre‐exercise value (mean±SD) (81.1±7.4 mmol · kg−1 DM), whereas after the 5 × 6 s sprints, PCr concentration was, respectively, 27% (10 s; P<0.01), 45% (30 s; P<0.01) and 84% (3 min; P<0.01) of the pre‐exercise value (77.1±4.9 mmol · kg−1 DM). PCr concentration was correlated with muscle lactate at 30 s (r=−0.82; P<0.05) and 3 min of recovery (r=−0.94; P<0.01) for the 1 × 6 s sprint, but not for the 5 × 6 s sprints. The extent of PCr repletion was significantly greater after the 5 × 6 s sprints than the 1 × 6 s sprint between both 10 s and 30 s and 30 s and 3 min, despite lower PCr levels at 10 s, 30 s and 3 min following the 5 × 6 s sprints. Full repletion of PCr is likely to take longer after repeated sprints than single short sprints because of a greater degree of PCr depletion, such that replenishment must commence from lower PCr levels rather than because of slower rates of repletion.