Validation of a Trunk-mounted Accelerometer to Measure Peak Impacts during Team Sport Movements.

This study assessed the validity of an accelerometer to measure impacts in team sports. 76 participants completed a team sport circuit. Accelerations were collected concurrently at 100 Hz using an accelerometer and a 36-camera motion analysis system. The largest peak accelerations per movement were compared in 2 ways: i) pooled together and filtered at 13 different cut-off frequencies (range 6-25 Hz) to identify the optimal filtering frequency, and ii) the optimal cut-off frequency split into the 7 movements performed (n=532). Raw and 25-16 Hz filtering frequencies significantly overestimated and 6 Hz underestimated motion analysis peak accelerations (P <0.007). The 12 Hz filtered accelerometer data revealed the strongest relationship with motion analysis data (accuracy - 0.01±0.27 g, effect size - 0.01, agreement - 0.55 to 0.53 g, precision 0.27 g, and relative error 5.5%; P=1.00). The accelerometer underestimated peak accelerations during tackling and jumping, and overestimated during walking, jogging, sprinting and change of direction. Lower agreement and reduced precision were associated with sprinting, jumping and tackling. The accelerometer demonstrated an acceptable level of concurrent validity compared to a motion analysis system when filtered at a cut-off frequency of 12 Hz. The results advocate the use of accelerometers to measure movements in team sport.

Energy system interaction and relative contribution during maximal exercise.

There are 3 distinct yet closely integrated processes that operate together to satisfy the energy requirements of muscle. The anaerobic energy system is divided into alactic and lactic components, referring to the processes involved in the splitting of the stored phosphagens, ATP and phosphocreatine (PCr), and the nonaerobic breakdown of carbohydrate to lactic acid through glycolysis. The aerobic energy system refers to the combustion of carbohydrates and fats in the presence of oxygen. The anaerobic pathways are capable of regenerating ATP at high rates yet are limited by the amount of energy that can be released in a single bout of intense exercise. In contrast, the aerobic system has an enormous capacity yet is somewhat hampered in its ability to delivery energy quickly. The focus of this review is on the interaction and relative contribution of the energy systems during single bouts of maximal exercise. A particular emphasis has been placed on the role of the aerobic energy system during high intensity exercise. Attempts to depict the interaction and relative contribution of the energy systems during maximal exercise first appeared in the 1960s and 1970s. While insightful at the time, these representations were based on calculations of anaerobic energy release that now appear questionable. Given repeated reproduction over the years, these early attempts have lead to 2 common misconceptions in the exercise science and coaching professions. First, that the energy systems respond to the demands of intense exercise in an almost sequential manner, and secondly, that the aerobic system responds slowly to these energy demands, thereby playing little role in determining performance over short durations. More recent research suggests that energy is derived from each of the energy-producing pathways during almost all exercise activities. The duration of maximal exercise at which equal contributions are derived from the anaerobic and aerobic energy systems appears to occur between 1 to 2 minutes and most probably around 75 seconds, a time that is considerably earlier than has traditionally been suggested.

Energy system contribution during 200- to 1500-m running in highly trained athletes.

PURPOSE: The purpose of the present study was to profile the aerobic and anaerobic energy system contribution during high-speed treadmill exercise that simulated 200-, 400-, 800-, and 1500-m track running events. METHODS: Twenty highly trained athletes (Australian National Standard) participated in the study, specializing in either the 200-m (N = 3), 400-m (N = 6), 800-m (N = 5), or 1500-m (N = 6) event (mean VO2 peak [mL x kg(-1)-min(-1)] +/- SD = 56+/-2, 59+/-1, 67+/-1, and 72+/-2, respectively). The relative aerobic and anaerobic energy system contribution was calculated using the accumulated oxygen deficit (AOD) method. RESULTS: The relative contribution of the aerobic energy system to the 200-, 400-, 800-, and 1500-m events was 29+/-4, 43+/-1, 66+/-2, and 84+/-1%+/-SD, respectively. The size of the AOD increased with event duration during the 200-, 400-, and 800-m events (30.4+/-2.3, 41.3+/-1.0, and 48.1+/-4.5 mL x kg(-1), respectively), but no further increase was seen in the 1500-m event (47.1+/-3.8 mL x kg(-1)). The crossover to predominantly aerobic energy system supply occurred between 15 and 30 s for the 400-, 800-, and 1500-m events. CONCLUSIONS: These results suggest that the relative contribution of the aerobic energy system during track running events is considerable and greater than traditionally thought.

Effect of high intensity board training on upper body anaerobic capacity and short-lasting exercise performance.

Seven conditioned post-pubescent male subjects (VO2peak = 2.8 +/- 0.1 l.min-1) performed three high intensity board training sessions per week for an eight week period, followed by ten days of reduced training (taper). Subjects performed a 60 second all-out test, on a Biokinetic swim bench ergometer, on five occasions throughout the duration of the study. Testing occurred pre-training (T1), during the third week of training (T2), during the sixth week of training (T3), following eight weeks of training (T4), and post-taper (T5). Performance parameters as well as oxygen deficit (OD) were recorded during the 60 second all-out tests for the assessment of anaerobic capacity. Time trials were completed at times corresponding to T1, T3 and T5 over distances of 75, 140 and 250 metres. Over the duration of the study improvements of 17 percent (p < 0.05) and 60 percent (p < 0.01) were observed for Biokinetic swim bench mean power and peak power, respectively. Improvements in mean power and OD reached significance after five weeks of training. Improvements of 11 (p < 0.05), seven (p < 0.05) and six (p < 0.05) percent were noted from pre-training to post-taper for the 75, 140 and 250 metre time trials, respectively. Peak oxygen uptake improved by five percent from pre-training to post-taper which was almost significant at the 0.05 level (p = 0.052). Mean power correlated significantly with the 75 (r = -0.74, p < 0.05) and 140 (r = -0.79, p < 0.05) metre time trials, indicating that in-water performance and Biokinetic swim bench ergometry are well related. The ten day period of reduced training had no effect on performance parameters assessed during the 60 second all-out tests. It was concluded that improvements in the anaerobic energy systems, and associated performance in short-lasting exercise of high intensity, can be induced within five weeks of high intensity training with no decrements in the aerobic energy system.

Accumulated oxygen deficit during supramaximal all-out and constant intensity exercise.

Two studies were conducted to test the validity of an all-out procedure for the assessment of the maximal accumulated oxygen deficit (AOD). Subjects in study 1 (N = 9; VO2max = 57 +/- 3 ml.kg-1.min-1 [+/- SEM]) completed three supramaximal efforts on a cycle ergometer. Exhaustive exercise during an all-out isokinetic procedure (mean intensity of 149% VO2max) was compared with constant intensity exercise at approximately 110% and 125% VO2max. Subjects in study 2 (N = 12; VO2max = 55 +/- 3 ml.kg-1.min-1) completed a constant intensity test to exhaustion at approximately 110% VO2max and a 90 s all-out test on a Monark friction loaded cycle ergometer (mean intensity of 143% VO2max). The AOD within each study were not significantly different (study 1:43.9, 44.1, and 42.0 ml.kg-1 for the 110%, 125%, and all-out tests; study 2: 52.1 and 51.2 ml.kg-1 for the 110% and all-out tests, respectively; P > 0.05). The total amount of work was significantly greater the longer the test, the additional work being attributed to aerobic processes. The rate of both aerobic and anaerobic energy production in the first 30 s of exercise was directly related to exercise intensity and the protocol used. The results indicate that an all-out procedure provides a valid estimate of the maximal AOD and shows potential for a more complete assessment of anaerobic ability as traditional indices of high intensity exercise performance are also obtained.

Influence of training status on maximal accumulated oxygen deficit during all-out cycle exercise.

The influence of training status on the maximal accumulated oxygen deficit (MAOD) was used to assess the validity of the MAOD method during supra-maximal all-out cycle exercise. Sprint trained (ST; n = 6), endurance trained (ET; n = 8), and active untrained controls (UT; n = 8) completed a 90 s all-out variable resistance test on a modified Monark cycle ergometer. Pretests included the determination of peak oxygen uptake (VO2peak) and a series (5-8) of 5-min discontinuous rides at submaximal exercise intensities. The regression of steady-state oxygen uptake on power output to establish individual efficiency relationships was extrapolated to determine the theoretical oxygen cost of the supramaximal power output achieved in the 90 s all-out test. Total work output in 90 s was significantly greater in the trained groups (P < 0.05), although no differences existed between ET and ST. Anaerobic capacity, as assessed by MAOD, was larger in ST compared to ET and UT. While the relative contributions of the aerobic and anaerobic energy systems were not significantly different among the groups, ET were able to achieve significantly more aerobic work than the other two groups, while ST were able to achieve significantly more anaerobic work. Peak power and peak pedalling rate were significantly higher in ST. The results suggested that MAOD determined during all-out exercise was sensitive to training status and provided a useful assessment of anaerobic capacity. In our study sprint training, compared with endurance training, appeared to enhance significantly power output and high intensity performance over brief periods (up to 60 s), yet few overall differences in performance (i.e. total work) existed during 90 s of all-out exercise.

Variable resistance all-out test to generate accumulated oxygen deficit and predict anaerobic capacity.

A supramaximal variable resistance test over varying time intervals was evaluated as an instrument for the assessment of a number of anaerobic parameters, including the accumulated oxygen deficit (AOD). Eight active men [age, 22 +/- 1 (SEM 1) years, peak oxygen uptake, 53.1 (SEM 2.1) ml x kg-1 x min-1] completed three randomly ordered all-out sprints of 45-, 60- and 90-s duration. Two incremental pretests consisting of three 5-min stages at power outputs of 45, 135, 225 W and 90, 180, 270 W were performed to establish individual efficiency relationships [r = 0.996 (SEE 1.1) ml x kg-1 x min-1]. These relationships were used to estimate energy demand (millilitres per kilogram of oxygen equivalents in 15-s time intervals) during the supramaximal tests. The AOD for the 45 [47.6 (SEM 1.5) ml x kg-1], 60 [49.0 (SEM 1.8) ml x kg-1] and 90 s [49.6 (SEM 1.7) ml x kg-1] tests were significantly different only for the 45 and 90-s tests. Evaluation of the 90-s test indicated that maximal or near-maximal (98%) anaerobic energy release was achieved in 60 s, with the AOD beginning to plateau after this time. No significant differences among tests were found for peak power, time to peak power and peak pedalling rate. Differences in mean power, total work and relative power decrement were related to the length of the test.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced training volume and intensity maintain aerobic capacity but not performance in distance runners.

It has recently been shown that a 70% reduction in training volume, while maintaining training intensity, results in the maintenance of VO2 max and 5 km running performance in distance runners. The purpose of this study was to examine the effects of a 4 wk reduction in training volume and intensity in distance runners. Ten well-conditioned males (VO2max = 63.4 +/- 1.3 ml.kg-1 x min-1) underwent 4 wks of base training (BT) at their accustomed training distance (71.8 +/- 3.6 km.wk-1) and intensity (76% of total distance > 70% VO2max). Training volume (-66%), frequency (-50%), and intensity (all running < 70% VO2max) were then decreased for a 4 wk reduced training period (RT). Treadmill VO2max was unchanged with RT (p > 0.05) as were resting plasma volume, estimated from haemoglobin and haematocrit levels, and resting heart rate (HR). Submaximal treadmill exercise VO2 (l.min-1), ventilation and HR were also unchanged, however, submaximal exercise RER and blood lactate accumulation following 4 mins at 95% VO2max (8.39 vs 9.89 mmol.l-1) were significantly elevated by RT (p < 0.05). Estimated percent body fat also increased (10.4% vs 11.8%) (p < 0.05). Five km race completion time significantly increased from 16.6 +/- 0.3 mins at week 4 of BT to 16.8 +/- 0.3 mins (12 seconds) at week 4 of RT. Nine of the 10 subjects were slower after RT. It is concluded that aerobic capacity was maintained in these runners, despite the combined reduction in training volume and intensity. However, it appears that training intensity during RT is important for the maintenance of 5 km running performance.