Assessment of physical activity with a pedometer and its relationship with VO2max among adolescents in Switzerland.

OBJECTIVES: In the absence of a gold standard, the assessment of physical activity in children remains difficult. To record physical activity with a pedometer and to examine to what extent it is correlated with VO2max. METHODS: Survey on physical activity and fitness; 233 Swiss adolescents aged 11 to 15 carried a pedometer (Pedoboy) during seven consecutive days. VO2max was estimated through an endurance shuttle run test. RESULTS: The physical activity recorded by the pedometer did not vary from one day to the other (p > 0.05). The physical activity was higher among boys than among girls (p < 0.001) and higher among younger adolescents (6th versus 8th grade; p < 0.001). The correlation between physical activity and estimated VO2max was 0.30 (p < 0.01). CONCLUSIONS: The use of a pedometer to assess physical activity over one entire week is feasible among adolescents. The record provided by the pedometer gives an objective measure of the usual physical activity and, as such, is relatively well correlated with aerobic capacity.

A mathematical model to describe fat oxidation kinetics during graded exercise.

PURPOSE: The purpose of this study was to develop a mathematical model (sine model, SIN) to describe fat oxidation kinetics as a function of the relative exercise intensity [% of maximal oxygen uptake (%VO2max)] during graded exercise and to determine the exercise intensity (Fatmax) that elicits maximal fat oxidation (MFO) and the intensity at which the fat oxidation becomes negligible (Fatmin). This model included three independent variables (dilatation, symmetry, and translation) that incorporated primary expected modulations of the curve because of training level or body composition. METHODS: Thirty-two healthy volunteers (17 women and 15 men) performed a graded exercise test on a cycle ergometer, with 3-min stages and 20-W increments. Substrate oxidation rates were determined using indirect calorimetry. SIN was compared with measured values (MV) and with other methods currently used [i.e., the RER method (MRER) and third polynomial curves (P3)]. RESULTS: There was no significant difference in the fitting accuracy between SIN and P3 (P = 0.157), whereas MRER was less precise than SIN (P < 0.001). Fatmax (44 +/- 10% VO2max) and MFO (0.37 +/- 0.16 g x min(-1)) determined using SIN were significantly correlated with MV, P3, and MRER (P < 0.001). The variable of dilatation was correlated with Fatmax, Fatmin, and MFO (r = 0.79, r = 0.67, and r = 0.60, respectively, P < 0.001). CONCLUSIONS: The SIN model presents the same precision as other methods currently used in the determination of Fatmax and MFO but in addition allows calculation of Fatmin. Moreover, the three independent variables are directly related to the main expected modulations of the fat oxidation curve. SIN, therefore, seems to be an appropriate tool in analyzing fat oxidation kinetics obtained during graded exercise.

Effects of Intermittent Training on Anaerobic Performance and MCT Transporters in Athletes.

This study examined the effects of intermittent hypoxic training (IHT) on skeletal muscle monocarboxylate lactate transporter (MCT) expression and anaerobic performance in trained athletes. Cyclists were assigned to two interventions, either normoxic (N; n = 8; 150 mmHg PIO2) or hypoxic (H; n = 10; ∼3000 m, 100 mmHg PIO2) over a three week training (5×1 h-1h30.week-1) period. Prior to and after training, an incremental exercise test to exhaustion (EXT) was performed in normoxia together with a 2 min time trial (TT). Biopsy samples from the vastus lateralis were analyzed for MCT1 and MCT4 using immuno-blotting techniques. The peak power output (PPO) increased (p<0.05) after training (7.2% and 6.6% for N and H, respectively), but VO2max showed no significant change. The average power output in the TT improved significantly (7.3% and 6.4% for N and H, respectively). No differences were found in MCT1 and MCT4 protein content, before and after the training in either the N or H group. These results indicate there are no additional benefits of IHT when compared to similar normoxic training. Hence, the addition of the hypoxic stimulus on anaerobic performance or MCT expression after a three-week training period is ineffective.

Respiratory muscle training enhances maximal minute ventilation and forced vital capacity in adolescent athletes.

Introduction. Respiratory difficulties in athletes are common, especially in adolescents, even in the absence of exercise-induced bronchoconstriction. Immaturity of the respiratory muscles coupling at high respiratory rates could be a potential mechanism. Whether respiratory muscle training (RMT) can positively influence it is yet unknown. Goal. We investigate the effects of RMT on ventilation and performance parameters in adolescent athletes and hypothesize that RMT will enhance respiratory capacity. Methods. 12 healthy subjects (8 male, 4 female, 17±0.5 years) from a sports/study high school class, competitively involved in various sports (minimum of 10 hours per week) underwent respiratory function testing, maximal minute ventilation (MMV) measurements and a maximal treadmill incremental test with VO2max and ventilatory thresholds (VT1 and VT2) determination. They then underwent one month of RMT (4 times/week) using a eucapnic hyperventilation device, with an incremental training program. The same tests were repeated after RMT. Results. Subjects completed 14.8 sessions of RMT, with an increase in total ventilation per session of 211±29% during training. Borg scale evaluation of the RMT session was unchanged or reduced in all subjects, despite an increase in total respiratory work. No changes (p>0.05) were observed pre/post RMT in VO2max (53.4±7.5 vs 51.6±7.7 ml/kg/min), VT2 (14.4±1.4 vs 14.0±1.1 km/h) or Speed max at end of test (16.1±1.7 vs 15.8±1.7 km/h). MVV increased by 9.2% (176.7±36.9 vs 192.9±32.6 l/min, p<0.001) and FVC by 3.3% (6.70±0.75 vs 4.85±0.76 litres, p<0.05). Subjective evaluation of respiratory sensations during exercise and daily living were also improved. Conclusions. RMT improves MMV and FVC in adolescent athletes, along with important subjective respiratory benefits, although no changes are seen in treadmill maximal performance tests and VO2max measurements. RMT can be easily performed in adolescent without side effects, with a potential for improvement in training capacity and overall well-being.

Vibration training elicits a mixed aerobic and resistance-type exercise in sedentary subjects.

Objective. Vibration training (VT) is a new exercise method, with good acceptance among sedentary subjects, due to its passive principle: the machine moves the subject, not the opposite. We hypothesize that untrained subjects can benefit from a greater cardiovascular and metabolic stimulation than trained athletes, resembling classical aerobic-type activity, in addition of eliciting strength gains shown in diverse studies. Methods. 3 group of male subjects, inactive (SED), endurance trained athletes (END) and strength trained athletes (STR) underwent fitness (VO2max) and lower-body strength tests (isokinetic). Subjects were submitted to a session of oscillating VT, composed of 3 exercises (isometric half-squat, dynamic squat, dynamic squat with added load), each of 3 minutes duration, and repeated at 3 frequencies. VO2, heart rate and Borg scale were monitored. Results. 27 healthy subjects (10 SED, 9 END and 8 STR), mean age 24.5 (SED), 25.0 (STR) and 29.8 (END) were included. VO2max was significantly different as expected (47.9 vs. 52.9 vs. 63.9 ml/kg/min, resp. for SED, STR and END). Isokinetic dominant leg extensors strength was higher in STR (3.32 Nm/kg vs. 2.60 and 2.74 in SED and END). During VT, peak oxygen consumption (% of VO2max) attained was 59.3 in SED, 50.8 in STR and 48.0 in END (P<0.001 between SED and other subjects). Peak heart rate (% of heart rate max) was 82.7 in SED, 80.4 in STR and 72.4 in END. In SED, dynamic exercises without extra load elicited 51.0% of VO2max and 72.1% of heart rate max, and perceived effort reached 15.1/20. Conclusions. VT is an unconventional type of exercise, which has been shown to enhance strength, bone density, balance and flexibility. Users are attracted by the relative passivity. In SED, we show that VT elicits sufficient cardiovascular response to benefit overall fitness in addition to the known strength effects. VT's higher acceptance as an exercise in sedentary people, compared to jogging or cycling for example, can lead to better adherence to physical activity. Although long-term effects of VT on health are not avalaible, we believe this type of combination of aerobic and resistance-type exercise can be beneficial on multiple health parameters, especially cardiovascular health.

Responses to exercise in normobaric hypoxia: comparison of elite and recreational ski mountaineers.

PURPOSE: Hypoxia is known to reduce maximal oxygen uptake (VO(2max)) more in trained than in untrained subjects in several lowland sports. Ski mountaineering is practiced mainly at altitude, so elite ski mountaineers spend significantly longer training duration at altitude than their lower-level counterparts. Since acclimatization in hypobaric hypoxia is effective, the authors hypothesized that elite ski mountaineers would exhibit a VO2max decrement in hypoxia similar to that of recreational ski mountaineers. METHODS: Eleven elite (E, Swiss national team) and 12 recreational (R) ski mountaineers completed an incremental treadmill test to exhaustion in normobaric hypoxia (H, 3000 m, F(1)O(2) 14.6% ± 0.1%) and in normoxia (N, 485 m, F(1)O(2) 20.9% ± 0.0%). Pulse oxygen saturation in blood (SpO(2)), VO(2max), minute ventilation, and heart rate were recorded. RESULTS: At rest, hypoxic ventilatory response was higher (P < .05) in E than in R (1.4 ± 1.9 vs 0.3 ± 0.6 L · min⁻¹ · kg⁻¹). At maximal intensity, SpO(2) was significantly lower (P < .01) in E than in R, both in N (91.1% ± 3.3% vs 94.3% ± 2.3%) and in H (76.4% ± 5.4% vs 82.3% ± 3.5%). In both groups, SpO(2) was lower (P < .01) in H. Between N and H, VO(2max) decreased to a greater extent (P < .05) in E than in R (-18% and -12%, P < .01). In E only, the VO(2max) decrement was significantly correlated with the SpO(2) decrement (r = .74, P < .01) but also with VO(2max) measured in N (r = .64, P < .05). CONCLUSION: Despite a probable better acclimatization to altitude, VO(2max) was more reduced in E than in R ski mountaineers, confirming previous results observed in lowlander E athletes.

Response of bone metabolism related hormones to a single session of strenuous exercise in active elderly subjects

OBJECTIVE: To evaluate the effect of strenuous exercise on bone metabolism and related hormones in elderly subjects. METHODS: Twenty one active elderly subjects (11 men and 10 women; mean age 73.3 years) showing a mean theoretical Vo2max of 151.4% participated. Concentrations of plasma ionised calcium (iCa), serum intact parathyroid hormone (iPTH), 25-hydroxyvitamin D (25(OH)D), and 1.25-dihydroxy-vitamin D3 (1.25(OH)2D3), as well as the bone biochemical markers type I collagen C-telopeptide for bone resorption and osteocalcin and bone alkaline phosphatase for bone formation, were analysed before and after a maximal incremental exercise test. RESULTS: At basal level, iPTH was positively correlated with age (r = 0.56, p < 0.01) and negatively correlated with 25(OH)D (r = -0.50; p < 0.01) and 1.25(OH)2D3 (r = -0.47; p < 0.05). Moreover, 25(OH)D and 1.25(OH)2D3 levels were negatively correlated with age (r = -0.50, p < 0.01 and r = -0.53, p < 0.01, respectively). After exercise, iCa and 25(OH)D decreased (p < 0.001 and p = 0.01, respectively) while iPTH increased (p < 0.001). The levels of 1.25(OH)2D3, bone biochemical markers, haematocrit, and haemoglobin were unchanged. The variations in iCa and 25(OH)D were not related to age and/or sex. The iPTH variation was directly related to basal iPTH levels (p < 0.01) and indirectly related to age. CONCLUSIONS: In active elderly subjects, strenuous exercise disturbed calcium homeostasis and bone related hormones without immediate measurable effect on bone turnover. Although an increase in iPTH could have an anabolic action on bone tissue, our findings from our short term study did not allow us to conclude that such action occurred.

Effect of inspiratory threshold loading on ventilatory kinetics during constant-load exercise.

Humoral factors play an important role in the control of exercise hyperpnea. The role of neuromechanical ventilatory factors, however, is still being investigated. We tested the hypothesis that the afferents of the thoracopulmonary system, and consequently of the neuromechanical ventilatory loop, have an influence on the kinetics of oxygen consumption (VO2), carbon dioxide output (VCO2), and ventilation (VE) during moderate intensity exercise. We did this by comparing the ventilatory time constants (tau) of exercise with and without an inspiratory load. Fourteen healthy, trained men (age 22.6 +/- 3.2 yr) performed a continuous incremental cycle exercise test to determine maximal oxygen uptake (VO2max = 55.2 +/- 5.8 ml x min(-1) x kg(-1)). On another day, after unloaded warm-up they performed randomized constant-load tests at 40% of their VO2max for 8 min, one with and the other without an inspiratory threshold load of 15 cmH2O. Ventilatory variables were obtained breath by breath. Phase 2 ventilatory kinetics (VO2, VCO2, and VE) could be described in all cases by a monoexponential function. The bootstrap method revealed small coefficients of variation for the model parameters, indicating an accurate determination for all parameters. Paired Student's t-tests showed that the addition of the inspiratory resistance significantly increased the tau during phase 2 of VO2 (43.1 +/- 8.6 vs. 60.9 +/- 14.1 s; P < 0.001), VCO2 (60.3 +/- 17.6 vs. 84.5 +/- 18.1 s; P < 0.001) and VE (59.4 +/- 16.1 vs. 85.9 +/- 17.1 s; P < 0.001). The average rise in tau was 41.3% for VO2, 40.1% for VCO2, and 44.6% for VE. The tau changes indicated that neuromechanical ventilatory factors play a role in the ventilatory response to moderate exercise.

Hyperthermia and maximal oxygen uptake in men and women.

To compare the effect of hyperthermia on maximal oxygen uptake (VO2max) in men and women, VO2max was measured in 11 male and 11 female runners under seven conditions involving various ambient temperatures (Ta at 50% RH) and preheating designed to manipulate the esophageal (Tes) and mean skin (Tsk) temperatures at VO2max. The conditions were: 25 degrees C, no preheating (control); 25, 35, 40, and 45 degrees C, with exercise-induced preheating by a 20-min walk at approximately 33% of control VO2max; 45 degrees C, no preheating; and 45 degrees C, with passive preheating during which Tes and Tsk were increased to the same degree as at the end of the 20-min walk at 45 degrees C. Compared to VO2max (l x min(-1)) in the control condition (4.52+/-0.46 in men, 3.01+/-0.45 in women), VO2max in men and women was reduced with exercise-induced or passive preheating and increased Ta, approximately 4% at 35 degrees C, approximately 9% at 40 degrees C and approximately 18% at 45 degrees C. Percentage reductions (7-36%) in physical performance (treadmill test time to exhaustion) were strongly related to reductions in VO2max (r=0.82-0.84). The effects of hyperthermia on VO2max and physical performance in men and women were almost identical. We conclude that men and women do not differ in their thermal responses to maximal exercise, or in the relationship of hyperthermia to reductions in VO2max and physical performance at high temperature. Data are reported as mean (SD) unless otherwise stated.

Reliability and validity of physiological data obtained within a cycle-run transition test in age-group triathletes.

This study examined the validity and reliability of a sequential "Run-Bike-Run" test (RBR) in age-group triathletes. Eight Olympic distance (OD) specialists (age 30.0 ± 2.0 years, mass 75.6 ± 1.6 kg, run VO2max 63.8 ± 1.9 ml· kg(-1)· min(-1), cycle VO2peak 56.7 ± 5.1 ml· kg(-1)· min(-1)) performed four trials over 10 days. Trial 1 (TRVO2max) was an incremental treadmill running test. Trials 2 and 3 (RBR1 and RBR2) involved: 1) a 7-min run at 15 km· h(-1) (R1) plus a 1-min transition to 2) cycling to fatigue (2 W· kg(-1) body mass then 30 W each 3 min); 3) 10-min cycling at 3 W· kg(-1) (Bsubmax); another 1-min transition and 4) a second 7-min run at 15 km· h(-1) (R2). Trial 4 (TT) was a 30-min cycle - 20-min run time trial. No significant differences in absolute oxygen uptake (VO2), heart rate (HR), or blood lactate concentration ([BLA]) were evidenced between RBR1 and RBR2. For all measured physiological variables, the limits of agreement were similar, and the mean differences were physiologically unimportant, between trials. Low levels of test-retest error (i.e. ICC <0.8, CV<10%) were observed for most (logged) measurements. However [BLA] post R1 (ICC 0.87, CV 25.1%), [BLA] post Bsubmax (ICC 0.99, CV 16.31) and [BLA] post R2 (ICC 0.51, CV 22.9%) were least reliable. These error ranges may help coaches detect real changes in training status over time. Moreover, RBR test variables can be used to predict discipline specific and overall TT performance. Cycle VO2peak, cycle peak power output, and the change between R1 and R2 (deltaR1R2) in [BLA] were most highly related to overall TT distance (r = 0.89, p < 0. 01; r = 0.94, p < 0.02; r = 0.86, p < 0.05, respectively). The percentage of TR VO2max at 15 km· h(-1), and deltaR1R2 HR, were also related to run TT distance (r = -0.83 and 0.86, both p < 0.05).

Physiological differences between cycling and running

This review compares the differences in systemic responses (VO2max, anaerobic threshold, heart rate and economy) and in underlying mechanisms of adaptation (ventilatory and hemodynamic and neuromuscular responses) between cycling and running. VO2max is specific to the exercise modality. Overall, there is more physiological training transfer from running to cycling than vice-versa. Several other physiological differences between cycling and running are discussed: HR is different between the two activities both for maximal and sub-maximal intensities. The delta efficiency is higher in running. Ventilation is more impaired in cycling than running due to mechanical constraints. Central fatigue and decrease in maximal strength are more important after prolonged exercise in running than in cycling.

Maximal aerobic power during running and cycling in obese and non-obese children.

The maximal aerobic capacity while running and cycling was measured in 22 prepubertal children (mean age +/- SD 9.5 +/- 0.8 years): 14 obese (47.3 +/- 10 kg) and 8 non-obese (31.1 +/- 6.1 kg). Oxygen consumption (VO2) and carbon dioxide production were measured by an open circuit method. Steady state VO2 was determined at different levels of exercise up to the maximal power on the cycloergometer (92 W in obese and 77 W in non-obese subjects) and up to the maximal running speed on the treadmill at a 2% slope (8.3 km/h in obese and 9.0 km/h in lean children). Expressed in absolute values, the VO2max in obese children was significantly higher than in controls (1.55 +/- 0.29 l/min versus 1.23 +/- 0.22 l/min, p < 0.05) for the treadmill test and comparable in the two groups (1.4 +/- 0.2 l/min versus 1.16 +/- 0.2 l/min, ns) for the cycloergometer test. When VO2max was expressed per kg fat free mass, the difference between the two groups disappeared for both tests. These data suggest that obese children had no limitation of maximal aerobic power. Therefore, the magnitude of the workload prescribed when a physical activity program is intended for the therapy of childhood obesity, it should be designed to increase caloric output rather than to improve cardiorespiratory fitness.

Energy expenditure of extreme competitive mountaineering skiing.

PURPOSE: Multi-hour ski mountaineering energy balance may be negative and intake below recommendations. METHODS: Athletes on the 'Patrouille des Glaciers' racecourses (17 on course Z, 27 km, +2,113 m; 11 on course A, 26 km, +1,881 m) volunteered. Pre-race measurements included body mass, stature, VO2max, and heart rate (HR) vs VO2 at simulated altitude; race measurements HR, altitude, incline, location, and food and drink intake (A). Energy expenditure (EE) was calculated from altitude corrected HR derived VO2. RESULTS: Race time was 5 h 7 min ± 44 min (mean ± SD, Z) and 5 h 51 min ± 53 min (A). Subjects spent 19.2 ± 3.2 MJ (Z), respectively, 22.6 ± 2.9 MJ (A) during the race. Energy deficit was -15.5 ± 3.9 MJ (A); intake covered 20 ± 7 % (A). Overall energy cost of locomotion (EC) was 9.9 ± 1.3 J m(-1) kg(-1) (Z), 8.0 ± 1.0 J m(-1) kg(-1) (A). Uphill EC was 11.7 ± 1 J m(-1) kg(-1) (Z, 13 % slope) and 15.7 ± 2.3 J m(-1) kg(-1) (A, 19 % slope). Race A subjects lost -1.5 ± 1.1 kg, indicating near euhydration. Age, body mass, gear mass, VO2max and EC were significantly correlated with performance; energy deficit was not. CONCLUSIONS: Energy expenditure and energy deficit of a multi-hour ski mountaineering race are very high and energy intake is below recommendations.

Vibration Training Elicits a Mixed Aerobic and Resistance-type Exercise in Sedentary Subjects

PURPOSE: We hypothesize that untrained subjects can benefit from a greater cardiovascular stimulation than trained athletes, resembling classical aerobic-type activity, in addition to eliciting strength gains.METHODS: 3 groups of male subjects, inactive (SED), endurance trained (END) and strength trained (STR) underwent fitness (VO2max) and lower-body strength tests (isokinetic). Subjects were submitted to a session of oscillating VT, composed of 3 exercises (isometric half-squat, dynamic squat, dynamic squat with added load), each of 3 minutes duration, and repeated at 3 vibration frequencies (20, 26 and 32 Hz). VO2, heart rate and Borg scale were monitored.RESULTS: 27 healthy subjects (10 SED, 9 END and 8 STR), mean age 24.5 (SED), 25.0 (STR) and 29.8 (END) were included. VO2max was significantly different as expected (47.9 vs. 52.9 vs. 63.9 mL?min-1?kg-1, resp. for SED, STR and END). Isokinetic dominant leg extensors strength was higher in STR (3.32 N?m?kg-1 vs. 2.60 and 2.74 in SED and END). During VT, peak oxygen consumption (% of VO2max) attained was 59.3 in SED, 50.8 in STR and 48.0 in END (P<0.001 between SED and other subjects). Peak heart rate (% of heart rate max) was 82.7 in SED, 80.4 in STR and 72.4 in END. In SED, dynamic exercises without extra load elicited 51.0 % of VO2max and 72.1 % of heart rate max, and perceived effort reached 15.1/20.CONCLUSIONS: VT is an unconventional type of exercise, known to enhance strength, bone density, balance and flexibility. Users are attracted by the relative passivity. In SED, VT elicits sufficient cardiovascular response to benefit overall fitness in addition to the strength effects. VT's higher acceptance as an exercise in sedentary people, compared to jogging or cycling, can lead to better adherence to physical activity. Although long-term effects of VT on health are not available, we believe this type of mixed aerobic and resistance-type exercise can be beneficial on multiple health parameters, especially cardiovascular health.

Réponses cardiorespiratoires lors d'une évaluation musculaire isocinétique du tronc

Objectif Évaluer les sollicitations cardiorespiratoires d'une évaluation isocinétique des muscles extenseurs/fléchisseurs du tronc. Méthode Huit sujets masculins (24,9±1,4ans) ont réalisé des exercices d'extension-flexion du rachis en mode isocinétique. Ce test comportait trois répétitions à 30°/s, trois répétitions à 60°/s et 15 répétitions à 120°/s en mode concentrique. Deux minutes de récupération étaient respectées entre chaque série. Des mesures de fréquence cardiaque, pression artérielle, consommation d'oxygène, et lactates sanguins étaient réalisées au repos et en fin d'exercice. Résultats Une augmentation significative de 84 % de la FC max, correspondant à 80 % de la FC maximale théorique a été mesurée. L'élévation de la TA systolique à l'effort correspondait à une augmentation de 20 % par rapport au repos. Une augmentation de 47 % de la VO2max a été mesurée. Le pic de lactates observé lors de la série de 15 répétitions montrait une augmentation significative de 230 % par rapport à la valeur de repos. La recherche de facteurs de risque cardiovasculaires doit être faite avant tout test isocinétique. Une épreuve d'effort conventionnelle peut être proposée aux patients à risque si une série correspondant à un test de résistance à la fatigue est envisagée.