Wade L. Knez

Ultra-Endurance Exercise and Oxidative Damage Implications for Cardiovascular Health

At least 30 minutes of moderate-intensity physical activity accumulated on most, preferably all days is considered the minimum level necessary to reduce the risk of developing cardiovascular disease. Despite an unclear explanation, some epidemiological data paradoxically suggest that a very high volume of exercise is associated with a decrease in cardiovascular health. Although ultra-endurance exercise training has been shown to increase antioxidant defences (and therefore confer a protective effect against oxidative stress), an increase in oxidative stress may contribute to the development of atherosclerosis via oxidative modification of low-density lipoprotein (LDL). Research has also shown that ultra-endurance exercise is associated with acute cardiac dysfunction and injury, and these may also be related to an increase in free radical production. Longitudinal studies are needed to assess whether antioxidant defences are adequate to prevent LDL oxidation that may occur as a result of increased free radical production during very high volumes of exercise. In addition, this work will assist in understanding the accrued effect of repeated ultra-endurance exercise-induced myocardial damage.

Relationship between laboratory-measured variables and heart rate during an ultra-endurance triathlon

The aim of the present study was to examine the relationship between the performance heart rate during an ultra-endurance triathlon and the heart rate corresponding to several demarcation points measured during laboratory-based progressive cycle ergometry and treadmill running. Less than one month before an ultra-endurance triathlon, 21 well-trained ultra-endurance triathletes (mean ± s: age 35 ± 6 years, height 1.77 ± 0.05 m, mass 74.0 ± 6.9 kg,   =  4.75 ± 0.42 l · min−1) performed progressive exercise tests of cycle ergometry and treadmill running for the determination of peak oxygen uptake ( ), heart rate corresponding to the first and second ventilatory thresholds, as well as the heart rate deflection point. Portable telemetry units recorded heart rate at 60 s increments throughout the ultra-endurance triathlon. Heart rate during the cycle and run phases of the ultra-endurance triathlon (148 ± 9 and 143 ± 13 beats · min−1 respectively) were significantly (P < 0.05) less than the second ventilatory thresholds (160 ± 13 and 165 ± 14 beats · min−1 respectively) and heart rate deflection points (170 ± 13 and 179 ± 9 beats · min−1 respectively). However, mean heart rate during the cycle and run phases of the ultra-endurance triathlon were significantly related to (r  =  0.76 and 0.66; P < 0.01), and not significantly different from, the first ventilatory thresholds (146 ± 12 and 148 ± 15 beats · min−1 respectively). Furthermore, the difference between heart rate during the cycle phase of the ultra-endurance triathlon and heart rate at the first ventilatory threshold was related to marathon run time (r  =  0.61; P < 0.01) and overall ultra-endurance triathlon time (r  =  0.45; P < 0.05). The results suggest that triathletes perform the cycle and run phases of the ultra-endurance triathlon at an exercise intensity near their first ventilatory threshold.

Markers of Muscle Damage and Performance Recovery after Exercise in the Heat

PURPOSE This study aimed to determine whether competitive intermittent exercise in the heat affects recovery, aggravates markers of muscle fiber damage, and delays the recovery of performance and muscle glycogen stores. METHODS Plasma creatine kinase, serum myoglobin, muscle glycogen, and performance parameters (sprint, endurance, and neuromuscular testing) were evaluated in 17 semiprofessional soccer players before, immediately after, and during 48 h of recovery from a match played in 43°C (HOT) and compared with a control match (21°C with similar turf and setup). RESULTS Muscle temperature was ∼1°C higher (P < 0.001) after the game in HOT compared with control and reached individual values between 39.9°C and 41.1°C. Serum myoglobin levels increased by more than threefold after the matches (P < 0.01), but values were not different in HOT compared with control, and they were similar to baseline values after 24 h of recovery. Creatine kinase was significantly elevated both immediately and 24 h after the matches, but the response after HOT was reduced compared with control. Muscle glycogen responses were similar across trials and remained depressed for more than 48 h after both matches. Sprint performance and voluntary muscle activation were impaired to a similar extent after the matches (sprint by ∼2% and voluntary activation by ∼1.5%; P < 0.05). Both of these performance parameters as well as intermittent endurance capacity (estimated by a Yo-Yo IR1 test) were fully recovered 48 h after both matches. CONCLUSION Environmental heat stress does not aggravate the recovery response from competitive intermittent exercise associated with elevated muscle temperatures and markers of muscle damage, delayed resynthesis of muscle glycogen, and impaired postmatch performance.

Six minute walk distance is greater when performed in a group than alone

Objective: To investigate whether the distance covered in the six minute walk test was affected by walking with a group of others in comparison with performing the test alone. Methods: Eight healthy men (mean (SD) age 21.0 (0.9) years) and eight healthy women (mean (SD) age 20.8 (2.0) years) performed in random order two six minute walk tests either alone or in a group of four on two separate occasions one week apart. Results: Distance covered increased significantly from a mean of 653 (61) m in the individual male tests to 735 (79) m in the male group tests (p<0.05), and 616 (75) m in the individual female tests to 701 (54) m in the female group tests (p<0.01). The men increased the distance walked in six minutes by 12.5% and the women by 13.7% when they performed the test as a group. Conclusion: Performing the six minute walk test in a group facilitates its execution.

An evaluation of 30-km cycling time trial (TT30)pacing strategy through time-to-exhaustion at average TT30 pace

Ham, DJ and Knez, WL. An evaluation of 30 km cycling time trial (TT30) pacing strategy through time-to-exhaustion at average TT30 pace. J Strength Cond Res 23(3): 1016-1021, 2009-A paucity of research is available on the optimal pacing strategy for cycling events longer than 4 km. Anecdotal evidence suggests that an even pacing strategy is most suitable; however, controlled studies have only determined that a slow start is more suitable than a fast start pacing strategy. Currently, it is unclear which strategy is more effective for endurance cycling time trials. This study sought to identify differences in 30-km cycling time trial (TT30) performance related to pacing strategies by comparing individually chosen pacing strategy with time-to-exhaustion (TE) at the average power output achieved during TT30. Eight moderately trained male cyclists (&OV0312;o2max = 50.9 ± 5.2 ml·kg−1·min−1) performed 2 TT30 tests and 2 TE tests at the average power output of TT30 on a Velotron cycle ergometer at the same time of day, separated by at least 48 hours. During TT30, participants generally chose to use a ‘fast start’ pacing strategy, cycling at a speed relative to the TT average (TTAvg) of 103.1 ± 2.2% during the first 5 km. There was no significant difference in performance time between the TE test and TT30. Starting pace (TT0-5) was significantly correlated with finishing pace (TT25-30) (r = −0.91; p < 0.01) and TE (r = 0.85; p < 0.01). Subjects cycling at a relative starting speed (RS0-5) >105% had a significantly longer TE than subjects cycling at <105%, whereas TT30 performance time was not different between the two groups. The present investigation provided indirect evidence that a fast start pacing strategy decreases finishing speed and overall performance in TT30, and increased TT performance can be achieved by selecting a starting pace no more than 5% above TTAvg.

Gender Differences in Fat Distribution and Inflammatory Markers among Arabs

Recent studies from the Gulf region suggest that compared to men, women have a greater risk of developing metabolic syndrome (MeS). Objective. To investigate gender differences in body composition, adipokines, inflammatory markers, and aerobic fitness in a cohort of healthy Qatari adults. Participants. Healthy Qatari (n = 58) were matched for age, gender, and body mass index. Methods. Body composition and regional fat distribution were determined by dual-energy X-ray absorptiometry and computerized tomography. Laboratory assessments included serum levels of fasting glucose, insulin, lipid profile analysis, adipokines, and inflammatory markers. Subjects were also evaluated for aerobic fitness. Results. Women had more adipose tissue in the total abdominal (P = 0.04) and abdominal subcutaneous (P = 0.07) regions compared to men. Waist circumference and indices of insulin sensitivity were similar; however, women had a more favourable lipid profile than men. Serum adiponectin and leptin levels were significantly higher in women, whereas inflammatory profiles were not different between men and women. Aerobic fitness was lower in women and was associated with abdominal fat accumulation. Conclusion. In premenopausal women, higher levels of adiponectin may support maintenance of insulin sensitivity and normolipidemia despite greater adiposity. However, poor aerobic fitness combined with abdominal fat accumulation may explain their greater future risk of MeS compared with men.

Effects of Electrical Muscle Stimulation on Oxygen Consumption

Electrical muscle stimulation (EMS) devices are being marketed as weight/ fat loss devices throughout the world. Commercially available stimulators have the ability to evoke muscle contractions that may affect caloric expenditure while the device is being used. The aim of this study was to test the effects of two different EMS devices (Abtronic and Feminique) on oxygen consumption at rest. Subjects arrived for testing after an overnight fast, had the devices fitted, and then positioned supine with expired air measured to determine oxygen consumption. After a 10-minute acclimation period, oxygen consumption was measured for 20 minutes with the device switched off (resting) then 20 minutes with the device switched on (stimulated). There were no significant differences (p > 0.05) in oxygen consumption between the resting and stimulated periods with either the Abtronic (mean +/- SD; resting, 3.40 +/- 0.44; stimulated, 3.45 +/- 0.53 ml of O(2).kg(-1).min(-1)) or the Feminique (resting, 3.73 +/- 0.45; stimulated, 3.75 +/- 0.46 ml of O(2).kg(-1).min(-1)). In summary, the EMS devices tested had no effect on oxygen consumption during muscle stimulation.

Greater Effect of East versus West Travel on Jet Lag, Sleep, and Team Sport Performance

Purpose This study aimed to determine the recovery timeline of sleep, subjective jet lag and fatigue, and team sport physical performance after east and west long-haul travel. Methods Ten physically trained men underwent testing at 0900 h and 1700 h local time on four consecutive days 2 wk before outbound travel (BASE), and the first 4 d after 21 h of outbound (WEST) and return (EAST) air travel across eight time zones between Australia and Qatar. Data collection included performance (countermovement jump, 20-m sprint, and Yo-Yo intermittent recovery level 1 [YYIR1] test) and perceptual (jet lag, motivation, perceived exertion, and physical feeling) measures. In addition, sleep was measured via wrist activity monitors and self-report diaries throughout the aforementioned data collection periods. Results Compared with the corresponding day at BASE, the reduction in YYIR1 distance after EAST was significantly different from the increase in WEST on day 1 after travel (P < 0.001). On day 2, significantly slower 20-m sprint times were detected in EAST compared with WEST (P = 0.03), with large effect sizes (ES) also indicating a greater reduction in YYIR1 distance in EAST compared with WEST (d = 1.06). Mean sleep onset and offset were significantly later and mean time in bed and sleep duration were significantly reduced across the 4 d in EAST compared with BASE and WEST (P < 0.05). Lastly, mean jet lag, fatigue, and motivation ratings across the 4 d were significantly worse in EAST compared with BASE and WEST (P < 0.05) and WEST compared with BASE (P < 0.05). Conclusions Long-haul transmeridian travel can impede team sport physical performance. Specifically, east travel has a greater detrimental effect on sleep, subjective jet lag, fatigue, and motivation. Consequently, maximal and intermittent sprint performance is also reduced after east travel, particularly within 72 h after arrival.

The time course for changes in leukocyte count in response to exercising in a hot environment

BACKGROUND: Poor lower limb stability during dynamic movement is thought to increase the risk of musculoskeletal injury. Biomechanically, stability is determined by a number of factors including the external load and contributions from passive and active tissues. One approach for studying lower limb stability is the single leg squat (SLS) test, which requires coordinated lower limb movement across a range of joint motions under external load. Although clinicians typically assess SLS quality from a single point of view (i.e. frontal plane), a 3D investigation of SLS kinematics would help to determine factors that differentiate clinician-defined “good” from “poor” quality performance. PURPOSE: To determine the kinematic parameters that characterise a good or a poor SLS performance in young adults. METHODS: 22 healthy young adults (13 male, 9 female; age: 23.8 ±3.1 years; height: 1.73 ±0.07 m; mass: 69.4 ±12.7 kg) free from musculoskeletal impairment were recruited. Video footage was collected in the frontal plane as participants performed three SLSs on each leg. SLS quality was assessed by a panel of physiotherapists using a ten-point ordinal scale. Performances were subsequently divided into tertiles corresponding to poor, intermediate and good SLS technique. 3D trajectories of 28 reflective markers attached to the pelvis, and lower limbs were simultaneously recorded at 200 Hz using a 10-camera, motion capture system (Vicon Motion Systems, Oxford, UK). Pelvis, hip and knee angles were calculated using a validated lower limb biomechanical model that incorporated functional identification of hip and knee joint centres. RESULTS: Mean rating of SLS quality as assessed by the panel of physiotherapists was 6.3±1.9 (range: 2.4 - 9.1). 3D analysis of SLS performance revealed that poor squatters had increased hip adduction (22.4 ±6.1 vs 14.7 ±4.7 deg, p<0.01), reduced knee flexion (73.1 ±8.7 vs 90.1 ±12.1 deg, p<0.01) and increased medal-lateral displacement of the knee joint centre (53.7 ±16.8 vs 38.4 ±14.3 mm, p=0.02) compared to good squatters. CONCLUSION: In healthy young adults a poor SLS is characterised by inadequate knee flexion and excessive frontal plane motion at the knee and hip. It is recommended that clinicians standardise knee flexion angle when using the SLS test as it might confound the perception of SLS quality.Purpose: To evaluate changes in performance and cardiac autonomic control (i.e. heart rate [HR] variability [HRV]) in elite soccer players during their pre-season training regime. Methods: Eight Spanish Premier League soccer players were examined at the first (week 1) and the last week (week 8) of the pre-season period (July-September). Nocturnal HR recordings on 4 days per week were averaged to evaluate the weekly HRV. Players also completed the Yo-Yo intermittent recovery test level 1 (Yo-Yo IR1) for the assessment of specific fitness. Results: During the pre-season period, there was no significant change (4.5 ± 23.9%) in Yo-Yo IR1 performance (2,475 ± 421 vs. 2,600 ± 786 m, p=0.55), while there was a significant decrement (6.3 ± 4.3%) in maximal HR (HRmax) recorded during the test (191 ± 7 vs. 179 ± 8 bpm, p = 0.004). Over the 8-week pre-season, significant increases in the standard deviation of the long-term continuous HRV (SD2) (174 ± 56 vs. 212 ± 53 ms, p = 0.017), and in the standard deviation of all HR intervals (SDNN) (135 ± 50 vs. 163 ± 41 ms, p = 0.023) were noted. No significant correlations were identified between Yo-Yo IR1 and HRV measures at week 1. In contrast, Yo-Yo IR1 performance was significantly correlated with SDNN (r =0.89, p=0.007) and SD2 (0.92, p=0.003) at week 8. Greater values in HRV at week 1 were substantially associated with lower HRV changes at the end of pre-season (r values ranged from -0.79 to -0.98, p< 0.05). Furthermore, HRV changes were significantly correlated with decreases in HRmax during the pre-season (r values from 0.83 to 0.94, p<0.05). Conclusions: The current results confirm that despite minimal changes in specific fitness (i.e. Yo-Yo IR1), pre-season training significantly improved various HRV indices in elite soccer players with greater changes evident for those with lower initial HRV levels. Nocturnal HRV may provide an important monitoring tool for identification of cardiovascular function changes in top-class soccer players during pre-season regimes.

329 Analysis of the physical requirements of tasks undertaken by Australian infantry soldiers and airfield defence guards

The Australian Defence Force (ADF) has resolved to establish a series of physical employment standards for Infantry soldiers and Airfield Defence Guards. A key stage in establishing these standards is to analyse the physical requirements of the two jobs. The purpose of this study was to analyse the physical requirements of the key physical tasks required within the two jobs. The jobs were divided into over 100 component tasks. Some tasks were common to the two jobs while others were specific to the respective jobs. ADF subject matter experts identified 36 tasks that were considered to be the most physically demanding. These tasks were observed to determine the movement patterns (actions) and muscle groups involved, the duration, velocity and estimated of exercise intensity. An estimate was also made of the involvement of each of seven activity types (endurance, strength-endurance etc) in each task and the exercise volume contained within each task. The tasks were ranked based upon the volume of work involved within each classification of activity type and movement action. Based upon these analyses, a series of tasks were chosen as those which best reflected the range of physical requirements of an Infantry soldier and an Airfield Defence Guard. These tasks were: marching while carrying support weapons, carrying ammunition boxes, assaulting, wall climbing, sandbagging, jumping from a height, pursuiting, rope climbing, patrolling in an urban environment, population protection, patrolling in marching order, building forced entry and stair climbing, casualty evacuation, loading stores and digging. Copyright