Eight male runners performed four 2-hr treadmill runs at 65% ~ 0 , m a x in the heat (35"C, 15-20% RH). A different beverage was offered each trial and subjects drank ad libitum for 2 min every 20 min. The beverages were, 6% carbohydrate (CHO) solution (NC 6), 6% carbonated-CHO solution (C 6), 10% CHO solution (NC 10), and 10% carbonated-CHO solution (C 10). NC 6 and C 6 contained 4% sucrose and 2% glucose. NC 10 and C 10 contained high fructose corn syrup. Subjects drank more NC 6 than C 6. Fluid consumption was not different among other trials. During all trials, volume consumed and %ΔPV declined while heart rate and rectal temperature increased (p<0.05). No significant differences occurred between beverages for these variables. Percent body weight lost was greater (p<0.05) for the C 10 trial compared to the NC 6 trial. Neither sweat rate, percent fluid replaced, plasma [Na+], [K+], osmolality, percent of drink volume emptied from the stomach, or glucose concentration differed among trials. Plasma [K+] and osmolality increased (p<0.05) over time. Ratings of fullness and thirst were not different among beverages, although both perceptions increased (p<0.05) with time. It is concluded that (a) carbonation decreased the consumption of the 6% CHO beverage; (b) fluid homeostasis and thermoregulation were unaffected by the solutions ingested; and (c) fluid consumption decreased with time, while ratings of fullness and thirst increased.
G. Patrick Lambert, Timothy L. Bleiler, Ray-Tai Chang, Alan K. Johnson and Carl V. Gisolfi
Jill A. Kanaley, Richard A. Boileau, Benjamin H. Massey and James E. Misner
Changes in muscular efficiency as it relates to age were examined during inclined submaximal treadmill walking in 298 boys ages 7–15 years. Furthermore, the changes in efficiency with increased work intensity (67–90% V̇O2max) were studied. Efficiency was expressed as submaximal oxygen consumption (V̇O2) and was calculated mathematically as energy out/energy in = (vertical distance) (wt of subject)/(V̇O2 L • min−1) (kcal equivalent). Efficiency, calculated mathematically, was found to significantly increase (p<.01) with age, with the younger children (<9 yrs) being less efficient than the older children (13–15 yrs). These values ranged from 12.8% for the youngest boys (<9 yrs) to 16.4% for the oldest boys (13–15 yrs). In addition, efficiency significantly increased in a linear fashion (p<.01) during submaximal workloads within each age group. No significant interactions (p>.05) between age and workload were found. These values are lower than gross efficiency values during cycling previously reported in the literature for adults; however, they support earlier findings that children increase in efficiency with age and work intensity, regardless if expressed as efficiency or V̇O2 (ml • kg−1 •min−1). These findings suggest that parameters associated with growth and development may influence muscular efficiency with age.
Mandy L. Gault, Richard E. Clements and Mark E.T. Willems
Cardiovascular responses of older adults to downhill (DTW, –10% incline) and level treadmill walking (0%) at self-selected walking speed (SSWS) were examined. Fifteen participants (age 68 ± 4 yr, height 1.69 ± 0.08 m, body mass 74.7 ± 8.1 kg) completed two 15-min walks at their SSWS (4.6 ± 0.6 km/hr). Cardiovascular responses were estimated using an arterial-volume finger clamp and infrared plethysmography. Oxygen consumption was 25% lower during DTW and associated with lower values for stroke volume (9.9 ml/beat), cardiac output (1.0 L/min), arteriovenous oxygen difference (a-v O2 diff, 2.4 ml/L), and systolic blood pressure (10 mmHg), with no differences in heart rate or diastolic and mean arterial blood pressure. Total peripheral resistance (TPR) was higher (2.11 mmHg) during DTW. During downhill walking, an exercise performed with reduced cardiac strain, endothelial changes, and reduced metabolic demand may be responsible for the different responses in TPR and a-v O2 diff. Future work is warranted on whether downhill walking is suitable for higher risk populations.
Michael W. Beets, Kenneth H. Pitetti and Bo Fernhall
The purpose of this study was to twofold: to determine reliability of peak performance as measured by peak heart rate (HRpeak) during the Progressive Cardiovascular Endurance Run (PACER) and a treadmill stress test (TM); and to compare the PACER and the TM. The sample consisted of 42 participants 8 to 21 years old with mild mental retardation. Participants completed two PACERs followed by two TMs separated by a minimum of 48 hr. Data collected were HR for the PACER and TM; PACER laps completed; and TM endurance time (min). Intraclass correlations were computed separately for males and females in order to assess the reliability of PACER laps, HRpeak, and TM time. Results indicated high reliability for both males and females on PACER laps and TM HRpeak, and for males on PACER HR and TM time; moderate reliability was observed for females on PACER HRpeak and TM time. No significant differences were detected within or among trials. These findings indicate that youth with mild mental retardation exhibit consistent peak performance on the PACER and TM tests; therefore, PACER can be used for surveillance of aerobic fitness in this population.
Dinesh John, Dixie L. Thompson, Hollie Raynor, Kenneth Bielak, Bob Rider and David R. Bassett
To determine if a treadmill-workstation (TMWS) increases physical activity (PA) and influences anthropometric, body composition, cardiovascular, and metabolic variables in overweight and obese office-workers.
Twelve (mean age= 46.2 ± 9.2 years) overweight/obese sedentary office-workers (mean BMI= 33.9 ± 5.0 kg·m-2) volunteered to participate in this 9-month study. After baseline measurements of postural allocation, steps per day, anthropometric variables, body composition, cardiovascular, and metabolic variables, TMWS were installed in the participants’ offices for their use. Baseline measurements were repeated after 3 and 9 months. Comparisons of the outcome variables were made using repeated-measures ANOVAs or nonparametric Friedman’s Rank Tests.
Between baseline and 9 months, significant increases were seen in the median standing (146−203 min·day-1) and stepping time (52−90 min·day-1) and total steps/day (4351−7080 steps/day; P < .05). Correspondingly, the median time spent sitting/lying decreased (1238−1150 min·day-1; P < .05). Using the TMWS significantly reduced waist (by 5.5 cm) and hip circumference (by 4.8 cm), low-density lipoproteins (LDL) (by 16 mg·dL-1), and total cholesterol (by 15 mg·dL-1) during the study (P < .05).
The additional PA energy expenditure from using the TMWS favorably influenced waist and hip circumferences and lipid and metabolic profiles in overweight and obese office-workers.
Rishann Nielson, Pat R. Vehrs, Gilbert W. Fellingham, Ronald Hager and Keven A. Prusak
The purposes of this study were to determine the accuracy and reliability of step counts and energy expenditure as estimated by a pedometer during treadmill walking and to clarify the relationship between step counts and current physical activity recommendations.
One hundred males (n = 50) and females (n = 50) walked at stride frequencies (SF) of 80, 90, 100, 110, and 120 steps/min, during which time step counts and energy expenditure were estimated with a Walk4Life Elite pedometer.
The pedometer accurately measured step counts at SFs of 100, 110, and 120 steps/min, but not 80 and 90 steps/min. Compared with energy expenditure as measured by a metabolic cart, the pedometer significantly underestimated energy expenditure at 80 steps/min and significantly overestimated measured energy expenditure at 90, 100, 110, and 120 steps/ min.
The pedometers’ inability to accurately estimate energy expenditure cannot be attributed to stride length entered into the pedometer or its ability to measure step counts. Males met 3 criteria and females met 2 criteria for moderate-intensity physical activity at SF of 110 to 120 steps/min. These results provide the basis for defining moderate-intensity physical activity based on energy expenditure and step counts and may lead to an appropriate steps/day recommendation.
Hazzaa M. Al-Hazzaa, Saeed A. Al-Refaee, Muhammed A. Sulaiman, Ma’ed Y. Dafterdar, Abdullah S. Al-Herbish and Andrew C. Chukwuemeka
The purpose of this study was to examine the maximal cardiorespiratory responses of trained adolescent male swimmers (SWM, N = 18), soccer players (SOC, N = 18), and moderately active reference subjects (CON, N = 16) to treadmill running (TRD) and arm ergometry (ARM). Mean values (±SD)for skeletal age were similar among the three groups (12.5± 1.9, 12.7 ± 1.1, and 12.5 ± 1.6 years, for the SWM, SOC, and CON, respectively). Allometric scaling procedures, relating VO2max and body mass, were used and mass exponents of .80 and .74 were identified for TRD and ARM data, respectively. During TRD testing SOC attained significantly higher VO2max values when expressed in ml · kg−1 · min−1, or ml · kg−0.80 · min−1 than the other two groups. However, during ARM testing, the SWM achieved significantly higher VO2peak values (ml · kg−0.74 · min−1 and scaled to arm-CSA) than SOC. The ratio of ARM-VAT to TRD-VAT was significantly higher in SWM (50.1± 9%) compared to SOC (41.2±5%), or CON (41.9 ± 6%).
John M. Schuna Jr., Tiago V. Barreira, Daniel S. Hsia, William D. Johnson and Catrine Tudor-Locke
Energy expenditure (EE) estimates for a broad age range of youth performing a variety of activities are needed.
106 participants (6–18 years) completed 6 free-living activities (seated rest, movie watching, coloring, stair climbing, basketball dribbling, jumping jacks) and up to 9 treadmill walking bouts (13.4 to 120.7 m/min; 13.4 m/min increments). Breath-by-breath oxygen uptake (VO2) was measured using the COSMED K4b2 and EE was quantified as youth metabolic equivalents (METy1:VO2/measured resting VO2, METy2:VO2/estimated resting VO2). Age trends were evaluated with ANOVA.
Seated movie watching produced the lowest mean METy1 (6- to 9-year-olds: 0.94 ± 0.13) and METy2 values (13- to 15-year-olds: 1.10 ± 0.19), and jumping jacks produced the highest mean METy1 (13- to 15-year-olds: 6.89 ± 1.47) and METy2 values (16- to 18-year-olds: 8.61 ± 2.03). Significant age-related variability in METy1 and METy2 were noted for 8 and 2 of the 15 evaluated activities, respectively.
Descriptive EE data presented herein will augment the Youth Compendium of Physical Activities.
William L. Siler and Philip E. Martin
In order to compare fast and slow runners with respect to the relative timing of the compensations they make to maintain a given running velocity during a prolonged effort, coordinate data were collected periodically for 9 fast and 10 slow volunteers performing a treadmill run to volitional exhaustion at a speed approximating their 10-km race pace. Statistically significant but small changes were noted in the average stride length, range of motion at the thigh, maximum thigh flexion, maximum knee extension, maximum knee flexion, and head-neck-trunk segment (HNT) angle at maximum thigh extension. No statistically significant differences were detected, however, with regard to the relative timing of the compensations demonstrated by the two groups. It was concluded that runners demonstrate subtle compensations in running pattern as they approach volitional exhaustion. In addition, it was concluded that the performance level of the runners as reflected by the ranges of 10-km run performance used in this investigation does not affect the relative timing of the compensations. Finally, it appears that some individuals are more sensitive to the effects of fatigue as evidenced by extreme compensations in running pattern.
Kenneth R. Turley and Jack H. Wilmore
This study investigated whether cardiovascular responses at a given submaximal oxygen consumption (V̇O2, L · min-1) are different between the treadmill (TM) and cycle ergometer (CE). Submaximal cardiovascular measurements were obtained at three work rates on both the TM and CE in 7- to 9-year-old children (12 males and 12 females). Using regression analysis, it was determined that there were no differences between the TM and CE in cardiac output (L · min-1), stroke volume (SV, ml · beat-1) or heart rate (beats · min-1) at a given V̇O2 (L · min-1). There were differences in the total peripheral resistance (TPR, units) and arterial-venous oxygen difference (a-vO2 diff, ml · 100 ml-1) to V̇O2 (L · min-1) relationship. While there were statistically significant differences in TPR and a-vO2 diff between the two modalities, there was substantial overlap of individual values at any given submaximal V̇O2, thus the physiological significance is questionable. Hence, we conclude that in 7- to 9-yearold children there are no differences in submaximal cardiovascular responses between the CE and TM.