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 10-20 m 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.

Physiology of small-sided games training in football: a systematic review

Small-sided games (SSGs) are played on reduced pitch areas, often using modified rules and involving a smaller number of players than traditional football. These games are less structured than traditional fitness training methods but are very popular training drills for players of all ages and levels. At present, there is relatively little information regarding how SSGs can best be used to improve physical capacities and technical or tactical skills in footballers. However, many prescriptive variables controlled by the coach can influence the exercise intensity during SSGs. Coaches usually attempt to change the training stimulus in SSGs through altering the pitch area, player number, coach encouragement, training regimen (continuous vs interval training), rules and the use of goalkeepers. In general, it appears that SSG exercise intensity is increased with the concurrent reduction in player number and increase in relative pitch area per player. However, the inverse relationship between the number of players in each SSG and exercise intensity does not apply to the time-motion characteristics. Consistent coach encouragement can also increase training intensity, but most rule changes do not appear to strongly affect exercise intensity. The variation of exercise intensity measures are lower in smaller game formats (e.g. three vs three) and have acceptable reproducibility when the same game is repeated between different training sessions or within the same session. The variation in exercise intensity during SSGs can also be improved with consistent coach encouragement but it is still more variable than traditional generic training methods. Other studies have also shown that SSGs containing fewer players can exceed match intensity and elicit similar intensities to both long- and short-duration high-intensity interval running. It also appears that fitness and football-specific performance can be improved equally with SSG and generic training drills. Future research is required to examine the optimal periodization strategies of SSGs training for the long-term development of physiological capacity, technical skill and tactical proficiency.

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 men's field-hockey team (age 26+/-3 years, body mass 76.7+/-5.6 kg, VO2max 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.

Excessive transforming growth factor-β signaling is a common mechanism in osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a heritable disorder, in both a dominant and recessive manner, of connective tissue characterized by brittle bones, fractures and extraskeletal manifestations. How structural mutations of type I collagen (dominant OI) or of its post-translational modification machinery (recessive OI) can cause abnormal quality and quantity of bone is poorly understood. Notably, the clinical overlap between dominant and recessive forms of OI suggests common molecular pathomechanisms. Here, we show that excessive transforming growth factor-β (TGF-β) signaling is a mechanism of OI in both recessive (Crtap(-/-)) and dominant (Col1a2(tm1.1Mcbr)) OI mouse models. In the skeleton, we find higher expression of TGF-β target genes, higher ratio of phosphorylated Smad2 to total Smad2 protein and higher in vivo Smad2 reporter activity. Moreover, the type I collagen of Crtap(-/-) mice shows reduced binding to the small leucine-rich proteoglycan decorin, a known regulator of TGF-β activity. Anti-TGF-β treatment using the neutralizing antibody 1D11 corrects the bone phenotype in both forms of OI and improves the lung abnormalities in Crtap(-/-) mice. Hence, altered TGF-β matrix-cell signaling is a primary mechanism in the pathogenesis of OI and could be a promising target for the treatment of OI.

Accuracy and reliability of a Cosmed K4b2 portable gas analysis system

The purpose of this study was to assess the validity and reliability of a Cosmed K4b2 portable telemetric gas analysis system. Twelve physically fit males performed a treadmill running session consisting of an easy 10 min run, a hard 3 min run and a 1 min sprint (with rest periods of 10 min separating each run), on four separate occasions. Sessions were identical with the exception of the apparatus used to measure VO2. During two (test-retest) sessions a Cosmed K4b2 portable gas analysis system was used; in another, a laboratory metabolic cart and, in one session, both systems were used to measure VO2 simultaneously. Comparison of Cosmed K4b2 and metabolic cart measurements in isolation revealed significantly (p < 0.05) increased values of VO2, VCO2, FE CO2 (except FE CO2 at 10 min) and lower values of FE O2 for each run duration by the Cosmed system. Linear regression equations to predict metabolic cart results from Cosmed values were, respectively; cart VO2 = 0.926 (Cosmed VO2-0.227 (r2 = 0.84) and cart VCO2 = 1.057 (Cosmed VCO2-0.606 (r2 = 0.92). Bland-Altman plots and comparison of the test-retest cosmed measurements revealed that the K4b2 system showed good repeatability of measurement for measures of VE, VO2 and VCO2, particularly for 10 min and 3 min tests (ICC = 0.7-0.9, p < 0.05). In conclusion, the Cosmed K4b2 portable gas analysis system recorded consistently higher VO2 and VCO2 measurements in comparison to a metabolic cart. However, satisfactory test-retest reliability of the system was demonstrated.

Iridium Luminophore Complexes for Unimolecular Oxygen Sensors

In this study, a series of novel luminescent cyclometalated Ir(III) complexes has been synthesized and evaluated for use in unimolecular oxygen-sensing materials. The complexes Ir(C6)(2)(vacac), 1, Ir(ppy)(2)(vacac), 2, fac-Ir(ppy)(2)(vppy), 3, and mer-Ir(ppy)(2)(vppy), 4, where C6 = Coumarin 6, vacac = allylacetoacetate, ppy = 2-phenylpyridine, and vppy = 2-(4-vinylphenyl)pyridine, all have pendent vinyl or allyl groups for polymer attachment via the hydrosilation reaction. These luminophore complexes were characterized by NMR, absorption, and emission spectroscopy, luminescence lifetime and quantum yield measurements, elemental analysis, and cyclic voltammetry. Complex 1 was structurally characterized using X-ray crystallography, and a series of 1-D ((1)H, (13)C) and 2-D ((1)H-(1)H, (1)H-(13)C) NMR experiments were used to resolve the solution structure of 4. Complexes 1 and 3 displayed the longest luminescence lifetimes and largest quantum efficiencies in solution (tau = 6.0 micros, phi = 0.22 for 1; tau = 0.4 micros, phi = 0.2 for 3) and, as result, are the most promising candidates for future luminescence-quenching-based oxygen-sensing studies.

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.

Training and game loads and injury risk in elite Australian footballers

OBJECTIVES

To examine the relationship between combined training and game loads and injury risk in elite Australian footballers.

DESIGN

Prospective cohort study.

METHODS

Forty-six elite Australian footballers (mean±SD age of 22.2±2.9 y) from one club were involved in a one-season study. Training and game loads (session-RPE multiplied by duration in min) and injuries were recorded each time an athlete exerted an exercise load. Rolling weekly sums and week-to-week changes in load were then modelled against injury data using a logistic regression model. Odds ratios (OR) were reported against a reference group of the lowest training load range.

RESULTS

Larger 1 weekly (>1750 AU, OR=2.44-3.38), 2 weekly (>4000 AU, OR=4.74) and previous to current week changes in load (>1250 AU, OR=2.58) significantly related (p<0.05) to a larger injury risk throughout the in-season phase. Players with 2-3 and 4-6 years of experience had a significantly lower injury risk compared to 7+ years players (OR=0.22, OR=0.28) when the previous to current week change in load was more than 1000 AU. No significant relationships were found between all derived load values and injury risk during the pre-season phase.

CONCLUSIONS

In-season, as the amount of 1-2 weekly load or previous to current week increment in load increases, so does the risk of injury in elite Australian footballers. To reduce the risk of injury, derived training and game load values of weekly loads and previous week-to-week load changes should be individually monitored in elite Australian footballers.

Accelerometer and GPS-derived running loads and injury risk in elite Australian footballers

The purpose of this study was to investigate the relationship between overall physical workload (global positioning systems [GPS]/accelerometer) measures and injury risk in elite Australian football players (n = 46) during a season. Workload data and (intrinsic) injury incidence were monitored across preseason and in-season (18 matches) phases. Multiple regression was used to compare cumulative (1-, 2-, 3-, and 4-weekly loads) and absolute change (from previous-to-current week) in workloads between injured and uninjured players for all GPS/accelerometer-derived variables: total distance, V1 distance (total distance above individual's aerobic threshold speed), sprint distance, force load, velocity load, and relative velocity change. Odds ratios (ORs) were calculated to determine the relative injury risk. Cumulative loads showed the strongest relationship with greater intrinsic injury risk. During preseason, 3-weekly distance (OR = 5.489, p = 0.008) and 3-weekly sprint distance (OR = 3.667, p = 0.074) were most indicative of greater injury risk. During in-season, 3-weekly force load (OR = 2.530, p = 0.031) and 4-weekly relative velocity change (OR = 2.244, p = 0.035) were associated with greater injury risk. No differences in injury risk between years of Australian Football League system experience and GPS/accelerometer data were seen. From an injury risk (prevention) perspective, these findings support consideration of several GPS/accelerometer running load variables in Australian football players. In particular, cumulative weekly loads should be closely monitored, with 3-weekly loads most indicative of a greater injury risk across both seasonal phases.

Mutations in SERPINF1 cause osteogenesis imperfecta type VI

Osteogenesis imperfecta (OI) is a spectrum of genetic disorders characterized by bone fragility. It is caused by dominant mutations affecting the synthesis and/or structure of type I procollagen or by recessively inherited mutations in genes responsible for the posttranslational processing/trafficking of type I procollagen. Recessive OI type VI is unique among OI types in that it is characterized by an increased amount of unmineralized osteoid, thereby suggesting a distinct disease mechanism. In a large consanguineous family with OI type VI, we performed homozygosity mapping and next-generation sequencing of the candidate gene region to isolate and identify the causative gene. We describe loss of function mutations in serpin peptidase inhibitor, clade F, member 1 (SERPINF1) in two affected members of this family and in an additional unrelated patient with OI type VI. SERPINF1 encodes pigment epithelium-derived factor. Hence, loss of pigment epithelium-derived factor function constitutes a novel mechanism for OI and shows its involvement in bone mineralization.

Proteoglycan 4 expression protects against the development of osteoarthritis

Osteoarthritis (OA) is a common degenerative condition that afflicts more than 70% of the population between 55 and 77 years of age. Although its prevalence is rising globally with aging of the population, current therapy is limited to symptomatic relief and, in severe cases, joint replacement surgery. We report that intra-articular expression of proteoglycan 4 (Prg4) in mice protects against development of OA. Long-term Prg4 expression under the type II collagen promoter (Col2a1) does not adversely affect skeletal development but protects from developing signs of age-related OA. The protective effect is also shown in a model of posttraumatic OA created by cruciate ligament transection. Moreover, intra-articular injection of helper-dependent adenoviral vector expressing Prg4 protected against the development of posttraumatic OA when administered either before or after injury. Gene expression profiling of mouse articular cartilage and in vitro cell studies show that Prg4 expression inhibits the transcriptional programs that promote cartilage catabolism and hypertrophy through the up-regulation of hypoxia-inducible factor 3α. Analyses of available human OA data sets are consistent with the predictions of this model. Hence, our data provide insight into the mechanisms for OA development and offer a potential chondroprotective approach to its treatment.

The influence of pacing strategy on VO2 and supramaximal kayak performance

PURPOSE

The purpose of this study was to investigate the effects of manipulating pacing strategy on VO2 and kayak ergometer performance in well-trained paddlers.

METHODS

Eight well-trained kayak paddlers (500-m time = 115-125 s) first performed a graded exercise test for determination of VO2max and lactate (La-) parameters. On subsequent days and in a random, counterbalanced order, subjects performed a 2-min, kayak ergometer test using either an all-out start or even pacing strategy.

RESULTS

There was a significantly greater peak power (747.6 +/- 152.0 vs 558.3 +/- 110.1 W) and average power (348.5 +/- 47.6 vs 335.5 +/- 44.8 W) using the all-out start strategy, when compared with the even-paced strategy. There was however, no significant difference between the two pacing strategies for peak VO2, accumulated oxygen deficit (AOD), peak [La-], or posttest pH. Using the all-out start, total VO2 was significantly greater (7.3 +/- 0.8 vs 6.9 +/- 0.8 L).

CONCLUSION

The results of this study indicate that 2-min kayak ergometer performance is significantly greater following an all-out start strategy when compared with an even-paced strategy. The improved performance appears to be attributable to faster VO2 kinetics, without a significant change in the total AOD (although the AOD distribution was altered).

Effects of caffeine on prolonged intermittent-sprint ability in team-sport athletes

PURPOSE

Caffeine can be a powerful ergogenic aid for the performance of prolonged, submaximal exercise. Little evidence, however, supports an ergogenic effect of caffeine on intermittent-sprint performance. Hence, this study was conducted to examine the effects of acute caffeine ingestion on prolonged intermittent-sprint performance.

METHODS

Using a double-blind, placebo-controlled design, 10 male team-sport athletes (amateur level, VO2peak 56.5 +/- 8.0 mL x kg(-1) x min(-1)) completed two exercise trials, separated by 7 d, 60 min after ingestion of either 6 mg x kg(-1) caffeine or placebo. The exercise trial was performed on a front-access cycle ergometer and consisted of 2 x 36-min halves, each composed of 18 x 4-s sprints with 2-min active recovery at 35% VO2peak between each sprint. Urinary caffeine levels were measured after exercise.

RESULTS

The total amount of sprint work performed during the caffeine trial was 8.5% greater than that performed during the placebo trial in the first half (75,165.4 +/- 3,902.9 vs 69,265.6 +/- 3,719.7 J, P < 0.05), and was 7.6% greater in the second half (73,978.7 +/- 4,092.6 vs 68,783.2 +/- 3,574.4 J, P < 0.05). Similarly, the mean peak power score achieved during sprints in the caffeine trial was 7.0% greater than that achieved during the placebo trial in the first half (1330.9 +/- 68.2 vs 1244.2 +/- 60.7 W, P < 0.05), and was 6.6% greater in the second half (1314.5 +/- 68.4 vs 1233.2 +/- 59.9 W, P < 0.05). Urinary caffeine levels following the caffeine trial ranged from 3.5 to 9.1 microg x mL(-1) (6.9 +/- 0.6 microg x mL(-1)).

CONCLUSION

This study revealed that acute caffeine ingestion can significantly enhance performance of prolonged, intermittent-sprint ability in competitive, male, team-sport athletes.

Player movement patterns and game activities in the Australian Football League

In the Australian Football League (AFL), specific game movements and activities have not been studied since the 1970s and 1980s and the game is now much faster than it was 20-30 years ago. Using lapsed-time video analysis, AFL players from five different positions (full forward/full back, centre half forward/centre half back, small forward/small back, mid fielders and ruckmen) had their movement patterns (stand, walk, jog, fast-run, sprint, change of direction) and game activities (possessions, ruck duels, ground ball contests, shepherds, spoils, bumps and tackles) recorded in two games each in the 2000 season. A descriptive analysis of the results was undertaken. The main findings were: full forward/full back were most different from the other positions, as they were seen to stand more and jog and fast-run less: ruckmen and midfielders were involved in more game activities than the other positions; for all positions, there were more than 150 high intensity movements (fast-run plus sprint) in the game, but these accounted for only 4-6% of total movement time: virtually all of the high intensity movements lasted for <6 secs; more than half of all sprints involved at least one change of direction, mostly within the 0-90 degrees arc (left or right) and all ground ball contests took <6 secs, with midfielders having 2-3 times as many as the other positions. Improvements in specific pre-season and in-season training practices for different positions should be possible after careful interpretation of these findings.

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.

Influence of cold water immersion on limb and cutaneous blood flow at rest

BACKGROUND

Cold water immersion reduces exercise-induced muscle damage. Benefits may partly arise from a decline in limb blood flow; however, no study has comprehensively investigated the influence of different degrees of cooling undertaken via cold water immersion on limb blood flow responses.

PURPOSE

To determine the influence of cold (8°C) and cool (22°C) water immersion on lower limb and cutaneous blood flow.

STUDY DESIGN

Controlled laboratory study.

METHODS

Nine men were placed in a semireclined position and lowered into 8°C or 22°C water to the iliac crest for two 5-minute periods interspersed with 2 minutes of nonimmersion. Rectal and thigh skin temperature, deep and superficial muscle temperature, heart rate, mean arterial pressure, thigh cutaneous blood velocity (laser Doppler), and superficial femoral artery blood flow (duplex ultrasound) were measured during immersion and for 30 minutes after immersion. Indices of vascular conductance were calculated (flux and blood flow/mean arterial pressure).

RESULTS

Reductions in rectal temperature (8°C, 0.2° ± 0.1°C; 22°C, 0.1° ± 0.1°C) and thigh skin temperature (8°C, 6.2° ± 0.5°C; 22°C, 3.2° ± 0.2°C) were greater in 8°C water than in 22°C (P < .01). Femoral artery conductance was reduced to a similar extent immediately after immersion (~30%) and 30 minutes after immersion (~40%) under both conditions (P < .01). In contrast, there was less thigh cutaneous vasoconstriction during and after immersion in 8°C water compared with 22°C (P = .01).

CONCLUSION

These data suggest that immersion at both temperatures resulted in similar whole limb blood flow but, paradoxically, more blood was distributed to the skin in the colder water. This suggests that colder temperatures may be associated with reduced muscle blood flow, which could provide an explanation for the benefits of cold water immersion in alleviating exercise-induced muscle damage in sports and athletic contexts.

CLINICAL RELEVANCE

Colder water temperatures may be more effective in the treatment of exercise-induced muscle damage and injury rehabilitation because of greater reductions in muscle blood flow.

Reliability of a repeated-sprint test for field-hockey

The purpose of this study was to assess the reliability of a repeated-sprint test, specifically designed for field-hockey, as it was based directly on the time-motion analysis of elite level competition. The test consisted of 6 x 30-m over-ground sprints departing on 25s, with an active recovery (approximately 3.1-3.3 ms(-1)) between sprints. Ten highly trained, male, field-hockey players (mean+/-S.D.: age, 23+/-3 years; body mass, 78.1+/-7.1 kg) participated in this study. Following familiarisation, the subjects performed the repeated-sprint test on two occasions, 7 days apart. The reliability of the test variables was assessed by the typical error of measurement (TE). The total sprint time was very reliable (T(1): 26.79+/-0.76 s versus T2: 26.83+/-0.74 s), as the TE was 0.7% (95% CL, 0.5-1.2%). However, the percent sprint decrement was less reliable (T1: 5.6+/-0.9% versus T2: 5.8+/-1.0%), with the TE being 14.9% (95% CL, 10.8-31.3%). In summary, it is suggested that this field-hockey-specific, repeated-sprint test is very reliable when the results are presented as the total sprint time.

Effect of hydrotherapy on recovery from fatigue

The present study investigated the effects of three hydrotherapy interventions on next day performance recovery following strenuous training. Twelve cyclists completed four experimental trials differing only in 14-min recovery intervention: cold water immersion (CWI), hot water immersion (HWI), contrast water therapy (CWT), or passive recovery (PAS). Each trial comprised five consecutive exercise days of 105-min duration, including 66 maximal effort sprints. Additionally, subjects performed a total of 9-min sustained effort (time trial - TT). After completing each exercise session, athletes performed one of four recovery interventions (randomly assigned to each trial). Performance (average power), core temperature, heart rate (HR), and rating of perceived exertion (RPE) were recorded throughout each session. Sprint (0.1 - 2.2 %) and TT (0.0 - 1.7 %) performance were enhanced across the five-day trial following CWI and CWT, when compared to HWI and PAS. Additionally, differences in rectal temperature were observed between interventions immediately and 15-min post-recovery; however, no significant differences were observed in HR or RPE regardless of day of trial/intervention. Overall, CWI and CWT appear to improve recovery from high-intensity cycling when compared to HWI and PAS, with athletes better able to maintain performance across a five-day period.

Iron status and the acute post-exercise hepcidin response in athletes

This study explored the relationship between serum ferritin and hepcidin in athletes. Baseline serum ferritin levels of 54 athletes from the control trial of five investigations conducted in our laboratory were considered; athletes were grouped according to values <30 μg/L (SF<30), 30-50 μg/L (SF30-50), 50-100 μg/L (SF50-100), or >100 μg/L (SF>100). Data pooling resulted in each athlete completing one of five running sessions: (1) 8 × 3 min at 85% vVO2peak; (2) 5 × 4 min at 90% vVO2peak; (3) 90 min continuous at 75% vVO2peak; (4) 40 min continuous at 75% vVO2peak; (5) 40 min continuous at 65% vVO2peak. Athletes from each running session were represented amongst all four groups; hence, the mean exercise duration and intensity were not different (p>0.05). Venous blood samples were collected pre-, post- and 3 h post-exercise, and were analysed for serum ferritin, iron, interleukin-6 (IL-6) and hepcidin-25. Baseline and post-exercise serum ferritin levels were different between groups (p<0.05). There were no group differences for pre- or post-exercise serum iron or IL-6 (p>0.05). Post-exercise IL-6 was significantly elevated compared to baseline within each group (p<0.05). Pre- and 3 h post-exercise hepcidin-25 was sequentially greater as the groups baseline serum ferritin levels increased (p<0.05). However, post-exercise hepcidin levels were only significantly elevated in three groups (SF30-50, SF50-100, and SF>100; p<0.05). An athlete's iron stores may dictate the baseline hepcidin levels and the magnitude of post-exercise hepcidin response. Low iron stores suppressed post-exercise hepcidin, seemingly overriding any inflammatory-driven increases.

Notch activation as a driver of osteogenic sarcoma

Osteogenic sarcoma (OS) is a deadly skeletal malignancy whose cause is unknown. We report here a mouse model of OS based on conditional expression of the intracellular domain of Notch1 (NICD). Expression of the NICD in immature osteoblasts was sufficient to drive the formation of bone tumors, including OS, with complete penetrance. These tumors display features of human OS; namely, histopathology, cytogenetic complexity, and metastatic potential. We show that Notch activation combined with loss of p53 synergistically accelerates OS development in mice, although p53-driven OS is not Rbpj dependent, which demonstrates a dual dominance of the Notch oncogene and p53 mutation in the development of OS. Using this model, we also reveal the osteoblasts as the potential sources of OS.

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

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; VO2max), sprint (10 m and 40 m times), sustained sprint (supramaximal treadmill run) and repeated sprint (6 x 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 VO2max (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.

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 x 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 x kg(-1) DM), whereas after the 5x6 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 x 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 1x6 s sprint, but not for the 5x6 s sprints. The extent of PCr repletion was significantly greater after the 5x6 s sprints than the 1x6 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 5x6 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.