Robert Kertzer

Physiological determinants of cross-country ski racing performance.

PURPOSE Previous laboratory testing has identified the importance of upper-body aerobic and anaerobic power to cross-country skiing performance. The purpose of this investigation was to extend laboratory research into a field setting to identify predictors of performance through ski-specific testing. METHODS Thirteen male collegiate skiers performed three field-testing sessions on roller skis to establish lactate threshold (LT) and ski economy (ECON) and maximal oxygen uptake (SK VO(2max)) and a 1-km double-pole time trial (UBTT) to determine peak upper-body oxygen uptake (UB VO(2)). As a measure of skiing performance, the subjects performed a 10-km skating time trial (TT) and were ranked according to competitive season performance (RANK). RESULTS Significant correlations (P < 0.05) were found between SK VO(2max), LT VO(2), UB VO(2), and RANK (r = -0.66 to -0.84) and TT time (r = -0.74 to -0.79), as well as ECON to RANK (r = 0.57) and TT time (r = 0.68). Time to complete the UBTT (UB time) exhibited the strongest correlation to both RANK (r = 0.95) and TT time (r = 0.92). Multiple regression analyses revealed that UB time was the best predictor of RANK and TT time, as demonstrated by the significant beta values (0.77, P < 0.001, and 0.79, P < 0.001, respectively). The importance of the UB component was further seen in that UB time was still the best predictor of performance when the subjects were divided into two distinct groups of greater and lesser competitive ability. CONCLUSIONS These findings identify the importance of the upper body component to cross-country skiing performance, suggesting a need to focus on upper-body conditioning within a well-rounded endurance training program. Additionally, the UBTT exhibits potential as a simple field test to predict cross-country skiing performance over more sophisticated and costly laboratory and field testing.

Postexercise oxygen consumption in trained females : effect of exercise duration

Many research studies report the long-lasting elevation of metabolism following exercise. However, little is known regarding the impact of duration and intensity on this phenomenon, particularly in trained women in whom the time of the menstrual cycle has been controlled. This study examined the effects of a constant walking intensity (70% of maximal oxygen uptake (VO2max)) on the treadmill at various levels of duration (20, 40, and 60 min) on 3-h recovery of oxygen uptake (VO2). Eight trained (mean +/- SD) (VO2max = 47.6 +/- 3.2 ml.kg-1.min-1) females (mean age = 30.2 +/- 5.0 yr, mean weight = 58.7 +/- 7.6 kg, mean height = 165.6 +/- 7.0 cm) participated in the study. Subjects reported to the lab for a maximal oxygen consumption test and returned on four additional occasions (control, 20, 40, 60 min) in random fashion. Treadmill speed and grade were established to yield the appropriate intensity for each subject. Following each exercise bout subjects sat quietly for a 3-h time period. Variables measured included VO2, minute ventilation (VE), respiratory exchange ratio (RER), heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), and core (rectal) temperature (Tc). Variables were measured each 15 min of recovery. An ANOVA was used to assess differences due to duration. Excess postexercise oxygen consumption (EPOC) was calculated by subtracting the resting VO2 from the absolute VO2 and summing the individual EPOCs during each 3-h postexercise session and comparing these individual values to the preexercise VO2 values. The EPOC was significantly elevated (P < 0.05) in each of the three durations as compared with the control (sitting) and preexercise periods. The total EPOC was significantly higher for the 60-min duration (15.2 l) as compared with either 20-min (8.b l) or 40-min (9.8 l) duration (P < 0.05). This was observed without significant changes in VE, RER, HR, SBP, DBP, or Tc. Additionally, there were no differences during exercise across the three durations in VO2, VE, RER, HR, SBP, DBP, or Tc. These data suggest that exercise duration increases EPOC significantly and that a 60-min duration yields approximately twice the EPOC than either 20 or 40 min.

Circuit weight training in cardiac patients: determining optimal workloads for safety and energy expenditure.

BACKGROUND While most studies suggest circuit weight training (CWT) to be safe in cardiac rehabilitation populations, few investigators have controlled variables known to impact CWT intensity. Therefore, the purposes of this study were to determine the energy cost and evaluate safety of cardiac patients while varying rest interval duration and lifting load in a CWT format. METHODS Nine male subjects with documented coronary artery disease had maximal oxygen uptake (VO2max), one-repetition maximum (1-RM), and body composition tested. In random order and on separate days, 4 CWT sessions using either 40% or 60% of the 1-RM, and either 30 or 60 seconds of rest between stations were completed. Energy cost, heart rate (HR), blood pressure (BP), and rate-pressure product (RPP) were measured. Data were analyzed with a repeated measures analysis of variance, and Tukeys post-hoc test was performed when significant results were found. The alpha level was set at < .05. RESULTS Subjects exercised at 25% to 32% of VO2max (58%-67% of HRmax) during CWT. The HR and RPP responses were lower during all CWT protocols than at 85% of the treadmill VO2max. No subject displayed any ST-segment depression or angina during CWT. The 40%-60-second protocol had an energy cost (2.98 kcal/min) that was lower (P < .05) than the other protocols (3.48-3.81 kcal/min). Increasing the lifting load resulted in increases (P < .05) in energy cost, and decreasing the rest interval increased energy cost only during the 40% 1-RM protocols. CONCLUSIONS Results indicate that CWT protocols of varied intensity are safe for cardiac patients when compared to treadmill exercise, and changes in rest interval duration and load can impact the energy cost.

Effects of exercise-training on the thermic effect of food and body fatness of adult women

Resting metabolic rate (RMR), thermic effect of food (TEF), aerobic capacity (VO2max), body fat, and food intake were measured in 10 healthy women before and after a 10 week graded exercise program of jogging. Pretraining TEF was a linear function of VO2max. Following exercise training, the women showed a significant increase (20%) in VO2max and loss (10.4%) of body fat; body weight did not change. Fat loss was directly related to changes in VO2max and RMR. The women showed a wide variation of changes in RMR (-21 to +2%) and TEF (-32 to +66%) from their pretraining levels. The changes in RMR and TEF were significantly positively correlated with improvements in VO2max. Analyses using multiple regression techniques, indicated that the changes in RMR and TEF accounted for 96.2% of the total variation in the changes of VO2max. Analyses of food intake indicated that diet composition (but not caloric intake) was highly related to the changes in VO2max, RMR, TEF and body fatness. Present results support further our hypothesis, that VO2max is an important physiological index of dietary thermogenesis and fat loss of individuals of normal body weight and fatness. Possible nutritional and physiological factors that may explain the wide variation in RMR and TEF of the women are discussed.

Physiologic responses of cardiac patients to supine, recumbent, and upright cycle ergometry

Physiological responses were compared in nine stable male cardiac patients (mean +/- standard error (SE): age, 68.3 +/- 8.1 years; height, 172.7 +/- 3.9cm; weight, 72.8 +/- 14.5kg) during stationary cycling in the supine, recumbent, and upright positions. A discontinuous exercise protocol was performed in which each stage included 3 minutes of exercise and 1 minute of recovery. Each subjects workload started at 150kgm.min-1 and increased by 150kgm.min-1 per stage until volitional fatigue. Testing sessions were randomized and performed 1 week apart. Subjects continued their normal medication regimen. All subjects were participants in a community-based cardiac rehabilitation program. Dependent variables were assessed at two different intensities; submaximal (300kgm.min +/- 1) and maximal. A two-way repeated measures ANOVA found no significant differences in systolic blood pressure (SBP), diastolic blood pressure (DBP), minute ventilation (VE), respiratory exchange ratio (R), rate pressure product (RPP), and rating of perceived exertion (RPE) at submaximal (300kgm.min +/- 1) and maximal exercise efforts. Heart rate (HR) was significantly lower (p < or = .05) in the supine position compared with either the upright or recumbent positions during the submaximal workload. In addition, oxygen uptake (VO2) was significantly lower in the supine position at the submaximal workload (p < or = .05) compared with both upright and recumbent. No difference in HR or VO2 was observed at maximal exercise. Regressions of HR on VO2 showed similar slopes and intercepts for supine, recumbent, and upright ergometry.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Prepubertal Physical Training on Growth, Voluntary Exercise, Cholesterol and Basal Metabolism in Rats.

Abstract Rats (N=180) were used as subjects in this investigation of the effects of prepubertal physical training on tibial growth, organ and body weights, serum cholesterol levels, basal metabolism, and voluntary exercise habits at puberty and 160 days postpuberty. The animals were assigned to one of three initial treatment groups: sedentary, voluntary exercise, or voluntary plus forced exercise. The sedentary animals were allowed no exercise, the voluntary-plus forced rats were allowed to run at will but also were forced to swim with weights on their tails for 30 minutes daily for 35 days just prior to puberty. At puberty 20 animals from each group were sacrificed. The remaining rats were allowed to exercise voluntarily for the next 160 days. After 160 days a second sacrifice of 10 animals from each group occurred. The trained rats at puberty had lower body weights, greater relative adrenal and testis weights, lower kidney weights, shorter tibias, lower serum cholesterol values, and lower levels of volu...

Lactic acid accumulation in cardiac patients performing circuit weight training: implications for exercise prescription.

OBJECTIVE Because blood lactic acid (LA) levels may be important in prescribing exercise for cardiac patients, this study documented the LA response to four different circuit weight training (CWT) protocols and compared these responses to both maximal treadmill and LA threshold values. DESIGN Intervention study following a crossover trial design. SETTING A phase III community-based setting. PATIENTS All subjects had documented cardiac disease and were volunteers. INTERVENTIONS We used 40% and 60% of the one-repetition maximum (1-RM) for six exercises and 30 or 60sec of rest between each station, resulting in four protocols, performed in random order. A discontinuous treadmill test was conducted, and the LA threshold was determined. MAIN OUTCOME MEASURE The main dependent variable was LA after each CWT protocol. RESULTS No signs or symptoms suggestive of cardiovascular distress during any of the four CWT protocols were reported. A repeated-measures analysis of variance showed that the LA threshold value was significantly less than all four CWT protocols (p < .05). The CWT responses were also compared with the traditional LA threshold value of 4.0mmol/L, and both 60% protocols were significantly elevated (p < .05). CONCLUSION Because no positive signs or symptoms were reported, we recommend starting stable cardiac patients on a CWT program with an initial load between 40% and 60% 1-RM and allowing at least 60sec of rest between exercises.

A Multichannel Telemetry System for Use in Exercise Physiology

A four-channel frequency-modulation radio-telemetry system for the measurement of two electrocardiograms (EKGs), respiration rate, and pulmonary ventilation of human subjects during vigorous exercise is described. From the measurement of pulmonary ventilation, the oxygen uptake (and thus energy expenditure) was predicted. This is the first time (to the authors knowledge) that oxygen consumption has been predicted by telemetry of pulmonary ventilation for such sports as squash, handball, and track. The transmitter uses pulse-duration modulation. It has a range of approximately 100 meters, which may be extended by using a whip antenna. Linearity of the system is 2 percent or better from a best straight line, and baseline drift is less than 1 percent at 25°C. The telemetry transmitter weighs approximately 100 grams and is contained in two boxes measuring 5 by 5 by 1.25 cm. Construction of this system is considerably simplified through extensive use of integrated circuits. A complete transmitter costs about

Strength Training in Female Distance Runners: Impact on Running Economy

50 (for components only) and dissipates approximately 60 mW. The batteries used provide a continuous life of 125 hours. The system has been used to obtain data from persons participating in squash, handball, track, and tennis. It may be used for many other physical activities.