Effect of concurrent strength and endurance training on skeletal muscle properties and hormone concentrations in humans

The purpose of this study was to investigate the effect of concurrent strength and endurance training on strength, endurance, endocrine status and muscle fibre properties. A total of 45 male and female subjects were randomly assigned to one of four groups; strength training only (S), endurance training only (E), concurrent strength and endurance training (SE), or a control group (C). Groups S and E trained 3 days a week and the SE group trained 6 days a week for 12 weeks. Tests were made before and after 6 and 12 weeks of training. There was a similar increase in maximal oxygen consumption (V˙O_{2 max}) in both groups E and SE (P < 0.05). Leg press and knee extension one repetition maximum (1 RM) was increased in groups S and SE (P < 0.05) but the gains in knee extension 1 RM were greater for group S compared to all other groups (P < 0.05). Types I and II muscle fibre area increased after 6 and 12 weeks of strength training and after 12 weeks of combined training in type II fibres only (P < 0.05). Groups SE and E had an increase in succinate dehydrogenase activity and group E had a decrease in adenosine triphosphatase after 12 weeks of training (P < 0.05). A significant increase in capillary per fibre ratio was noted after 12 weeks of training in group SE. No changes were observed in testosterone, human growth hormone or sex hormone binding globulin concentrations for any group but there was a greater urinary cortisol concentration in the women of group SE and decrease in the men of group E after 12 weeks of training (P < 0.05). These findings would support the contention that combined strength and endurance training can suppress some of the adaptations to strength training and augment some aspects of capillarization in skeletal muscle. Accepted: 10 November 1998     

The influence of either no fluid or carbohydrate-electrolyte fluid ingestion and the environment (thermoneutral versus hot and humid) on running economy after prolonged, high-intensity exercise

This study investigated the effects on running economy (RE) of ingesting either no fluid or an electrolyte solution with or without 6% carbohydrate (counterbalanced design) during 60-min running bouts at 80% maximal oxygen consumption (V˙O_2max). Tests were undertaken in either a thermoneutral (22–23°C; 56–62% relative humidity, RH) or a hot and humid natural environment (Singapore: 25–35°C; 66–77% RH). The subjects were 15 young adult male Singaporeans [V˙O_2max = 55.5 (4.4 SD) ml kg⁻¹ min⁻¹]. The RE was measured at 3 m s⁻¹ [65 (6)% V˙O_2max] before (RE1) and after each prolonged run (RE2). Fluids were administered every 2 min, at an individual rate determined from prior tests, to maintain body mass (group mean = 17.4 ml min⁻¹). The V˙O₂ during RE2 was higher (P < 0.05) than that during the RE1 test for all treatments, with no differences between treatments (ANOVA). The mean increase in V˙O₂ from RE1 to RE2 ranged from 3.4 to 4.7 ml kg⁻¹ min⁻¹ across treatments. In conclusion, the deterioration in RE at 3 m s⁻¹ (65% V˙O_2max) after 60 min of running at 80% V˙O_2max appears to occur independently of whether fluid is ingested and regardless of whether the fluid contains carbohydrates or electrolytes, in both a thermoneutral and in a hot, humid environment. Accepted: 30 October 1997     

V˙E and V˙CO2 remain tightly coupled during incremental cycling performed after a bout of high-intensity exercise

The purpose of the present study was to determine whether the linear relationship between CO₂ output (V˙CO₂) and pulmonary ventilation (V˙ _E) is altered during incremental cycling performed after exercise-induced metabolic acidosis. Ten untrained, female subjects performed two incremental cycling tests (15 W · min⁻¹ up to 165 W) on separate days. One incremental exercise test was conducted without prior exercise, whereas the other test was preceded by a 1-min bout of maximal cycling. The ventilatory equivalent for O₂ (V˙ _E/V˙O₂) was only elevated above control values at 15–60 W during incremental cycling performed after high-intensity exercise. In contrast, the ventilatory equivalent for CO₂ (V˙ _E/V˙CO₂) was significantly increased above control levels at nearly every work stage of incremental work (all except 165 W). Hyperventilation relative to V˙CO₂ was confirmed by the significantly lower end-tidal CO₂ tension (P _ETCO₂) obtained throughout the incremental cycling that was performed after high-intensity exercise (except at 165 W). V˙ _E and V˙CO₂ were significantly correlated under both treatment conditions (r > 0.99; P < 0.001). Moreover, both the slope and y-intercept of the linear regression were found to be significantly elevated during the incremental cycling performed after high-intensity cycling compared to control conditions (P < 0.01). The increase in the slope of the V˙ _E-V˙CO₂ relationship during incremental exercise performed under these conditions does not represent an uncoupling of V˙ _E from V˙CO₂, but could be accounted for by the significantly lower P _ETCO₂ observed during exercise. Accepted: 20 June 1997     

The effect of endurance training on the ventilatory response to exercise in elite cyclists

The purpose of this study was to investigate the effects of endurance training on the ventilatory response to acute incremental exercise in elite cyclists. Fifteen male elite cyclists [mean (SD) age 24.3 (3.3) years, height 179 (6) cm, body mass 71.1 (7.6) kg, maximal oxygen consumption (V˙O_2max) 69 (7) ml · min⁻¹ · kg⁻¹] underwent two exercise tests on a cycle ergometer. The first test was assessed in December, 6 weeks before the beginning of the cycling season. The second test was performed in June, in the middle of the season. During this period the subjects were expected to be in a highly endurance-trained state. The ventilatory response was assessed during an incremental exercise test (20 W · min⁻¹). Oxygen consumption (V˙O₂), carbon dioxide production (V˙CO₂), minute ventilation (V˙ _E), and heart rate (HR) were assessed at the following points during the test: at workloads of 200 W, 250 W, 300 W, 350 W, 400 W and at the subject's maximal workload, at a respiratory exchange ratio (R) of 1, and at the ventilatory threshold (Th_vent) determined using the V-slope-method. Post-training, the mean (SD) V˙O_2max was increased from the pre-training level of 69 (7) ml · min⁻¹ · kg⁻¹ (range 61.4–78.6) to 78 (6) ml · min⁻¹ · kg⁻¹ (range 70.5–86.3). The mean post-training V˙O₂ was significantly higher than the pre training value (P < 0.01) at all work rates, at Th_vent and at R=1. V˙O₂ was also higher at all work rates except for 200 W and 250 W. V˙ _E was significantly higher at Th_vent and R=1. Training had no effect on HR at all workloads examined. An explanation for the higher V˙O₂ cost for the same work rate may be that in the endurance-trained state, the adaptation to an exercise stimulus with higher intensity is faster than for the less-trained state. Another explanation may be that at the same work rate, in the less-endurance-trained state power is generated using a significantly higher anaerobic input. The results of this study suggest the following practical recommendations for training management in elite cyclists: (1) the V˙O₂ for a subject at the same work rate may be an indicator of the endurance-trained state (i.e., the higher the V˙O₂, the higher the endurance-trained capacity), and (2) the need for multiple exercise tests for determining the HR at Th_vent during a cycling season is doubtful since at Th_vent this parameter does not differ much following endurance training. Accepted: 19 October 1999     

Benefit of endurance training in elderly people over a short period is reversible

 The present study assessed daily activity, physical capacity and body composition in 11 initially sedentary healthy subjects [5 men and 6 women, mean age 62.8 (SD 2.7) years] before training (T_o), after completion of 7 (T_7w) and 14 (T_14w) weeks of training, and again 6 (T_6m) and 12 (T_12m) months after training. The mean daily activity index decreased from T_7w to T_12m reaching a lower level than at T_o [T_12m − T_o = −1.5 (SD 4.6) units, P = 0.18]. Mean maximal oxygen uptake (V˙O_2max) and its corresponding mean power output (W˙ _max) were increased by 12.5 (SD 6.6)% (P = 0.003) and 22.8 (SD 12.8)% (P = 0.003), respectively, at T_14w, and returned to their T_o levels within 1 year. Mean body mass (m _b) remained stable until T_6m but increased significantly by 2.6 (SD 3.7)% from T_6m to T_12m (P < 0.05). Mean fat mass (m _f, from bioelectrical impedance analysis measurements) tended to decrease [−2.0 (SD 4.2)%, P = 0.10] during the training period but increased by 7.8 (SD 10.9)% between T_6m and T_12m (P < 0.05). The mean fat free mass did not vary during the study period (P = 0.81) but magnetic resonance imaging (MRI) showed that mean thigh muscle volume decreased between T_7w and T_12m to less than at T_o [T_12m − T_o = −2.3 (SD 3.6)%, P = 0.05]. Therefore, this study confirmed the favourable effects of endurance training on the physical capacity and body composition of elderly people, but demonstrated that the training programme would have to be continued to maintain the training-related benefits (i.e. increased V˙O_2max and W˙ _max) which would otherwise be lost within 1 year. After training, m _b and m _f were found to be increased. Furthermore, a fast and reproducible MRI protocol was validated for study of small intra-individual variations in tissue volumes in longitudinal studies. Accepted: 7 September 1999     

Effects of improvement in aerobic power on resting insulin and glucose concentrations in children

In this study we determined the influence of improving aerobic power (V˙O_2max) on basal plasma levels of insulin and glucose of 11- to 14-year-old children, while accounting for body fat, gender, pubertal status, and leisure-time physical activity (LTPA) levels. Blood samples were obtained from 349 children after an overnight fast and analyzed for plasma insulin and glucose. Height, mass, body mass index (BMI), and sum of skinfolds (Σ triceps + subscapular sites) were measured. LTPA levels and pubertal status were estimated from questionnaires, and V˙O_2max was predicted from a cycle ergometry test. Regardless of gender, insulin levels were significantly correlated (P = 0.0001) to BMI, skinfolds, pubertal stage, and predicted V˙O_2max, but were not related to LTPA levels. Fasting glucose levels were not correlated to measures of adiposity or exercise (LTPA score, V˙O_2max) for females; however, BMI and skinfolds were correlated for males (P < 0.006). The children then took part in an 8-week aerobic exercise program. The 60 children whose V˙O_2max improved (≥3 ml · kg⁻¹ · min⁻¹) had a greater reduction in circulating insulin than the 204 children whose V˙O_2max did not increase −16 (41) vs −1 (63) pmol · l⁻¹; P = 0.028. The greatest change occurred in those children with the highest initial resting insulin levels. Plasma glucose levels were slightly reduced only in those children with the highest insulin levels whose V˙O_2max improved (P < 0.0506). The results of this study indicate that in children, adiposity has the most significant influence on fasting insulin levels; however, increasing V˙O_2max via exercise can lower insulin levels in those children with initially high levels of the hormone. In addition, LTPA does not appear to be associated with fasting insulin status, unless it is sufficient to increase V˙O_2max. Accepted: 2 June 1999     

Effect of exercise on the mitochondrial DNA content of peripheral blood in healthy women

Exercise decreases insulin resistance and increases maximal exercise capacity as estimated from maximal oxygen uptake (V˙O_2max). Recent reports have demonstrated that the mitochondrial DNA (mtDNA) content of blood is correlated with V˙O_2max in healthy subjects (mean age 31 years) and is inversely correlated with insulin resistance parameters. The aim of this study was to determine the effect of regular exercise on the mtDNA content in the peripheral blood of 16 healthy young women of mean age 24.8 (SD 6.2) years and 14 healthy older women of mean age 66.7 (SD 5.8) years. The exercise programme lasted for 10 weeks and consisted of three sessions a week, each of 1 h and aiming to attain 60%–80% of V˙O_2max. The mtDNA content of peripheral blood was measured by competitive polymerase chain reaction. The V˙O_2max had significantly increased following the exercise programme [from 33.1 (SD 3.4) to 35.2 (SD 3.4) ml · kg⁻¹ · min⁻¹ in the young and from 24.3 (SD 5.3) to 30.3 (SD 7.3) ml · kg⁻¹ · min⁻¹ in the older women, both P < 0.05]. Exercise decreased systolic blood pressure, and concentrations of triglyceride, low density lipoprotein-cholesterol (LDL-C), glucose and insulin in the blood of the young and of total cholesterol, LDL-C and glucose in that of the older women. High density lipoprotein-cholesterol (HDL-C) in the young women was increased by exercise. The mtDNA content significantly increased following the exercise programme in both groups [from 27.1 (SD 17.9) to 52.7 (SD 44.6) amol · 5 ng⁻¹ genomic DNA in the young and from 15.3 (SD 10.2) to 32.1 (SD 30.0) amol · 5 ng⁻¹ genomic DNA in the older women, both P < 0.05]. There was a significant positive correlation between the change in mtDNA content and the change in V˙O_2max (r=0.74 in the young and r=0.71 in the older women, both P < 0.01). In conclusion, 10 weeks of moderate intensity, regular exercise increased the mtDNA content in peripheral blood and decreased insulin resistance parameters. This data suggests that increase in the mtDNA content may be associated with increased insulin sensitivity. Accepted: 15 April 2000     

Gas exchange responses to continuous incremental cycle ergometry exercise in primary pulmonary hypertension in humans

In patients suffering from primary pulmonary hypertension (PPH), a raised pulmonary vascular resistance may limit the ability to increase pulmonary blood flow as work rate increases. We hypothesised that oxygen uptake (V˙O₂) may not rise appropriately with increasing work rate during incremental cardiopulmonary exercise tests. Nine PPH patients and nine normal subjects performed symptom-limited maximal continuous incremental cycle ergometry exercise. Mean peak V˙O₂ [1.00 (SD 0.22) compared to 2.58 (SD 0.64) l · min⁻¹] and mean V˙O₂ at lactic acidosis threshold [LAT, 0.73 (SD 0.17) compared to 1.46 (SD 0.21 · l) ml · min⁻¹] were much lower in patients than in normal subjects (both P < 0.01, two-way ANOVA with Tukey test). The mean rate of change of V˙O₂ with increasing work rate above the LAT [5.9 (SD 2.1) compared to 9.4 (SD 1.3) ml · min⁻¹ · W⁻¹, P < 0.01)] was also much lower in patients than in normal subjects [apparent δ efficiency 60.3 (SD 38.8)% in patients compared to 31.0 (SD 4.9)% in normal subjects]. The patients displayed lower mean values of end-tidal partial pressure of carbon dioxide than the normal subjects at peak exercise [29.7 (SD 6.8) compared to 42.4 (SD 5.8) mmHg, P < 0.01] and mean oxyhaemoglobin saturation [89.1 (SD 4.1) compared to 93.6 (SD 1.8)%, P < 0.05]. Mean ventilatory equivalents for CO₂ [49.3 (SD 11.4) compared to 35.0 (SD 7.3), P < 0.05] and O₂ [44.2 (SD 10.7) compared to 29.9 (SD 5.1), P < 0.05] were greater in patients than normal subjects. The sub-normal slopes for the V˙O₂-work-rate relationship above the LAT indicated severe impairment of the circulatory response to exercise in patients with PPH. The ventilatory abnormalities in PPH suggested that the lung had become an inefficient gas exchange organ because of impaired perfusion of the ventilated lung. Accepted: 17 April 2000     

Oxygen uptake efficiency slope as a useful measure of cardiorespiratory functional reserve in adult cardiac patients

In this study we aimed to elucidate the validity and usefulness of the oxygen uptake efficiency slope (OUES) in the evaluation of adult cardiac patients. Cardiopulmonary exercise tests were performed on a treadmill by 50 adult patients with chronic heart failure. The OUES was calculated from data for the first 75%, 90%, and 100% of exercise duration. The OUES is derived from the following equation: V˙O₂=a× logV˙ _E+b, where V˙O₂ is oxygen uptake (ml/kg/min), V˙ _E is minute ventilation (l/kg/min), and the constant “a” represents OUES. We also determined the ventilatory anaerobic threshold (VAT). The correlation coefficient of the logarithmic curve-fitting model was [mean (SD)] 0.986 (0.009). The OUES could be used to discriminate effectively between New York Heart Association functional classes (P < 0.001). OUES and maximum V˙O₂ were significantly correlated (r=0.78, P < 0.01). Agreement between the OUES values for the first 90%, 75%, and 100% of the exercise was excellent (intraclass correlation coefficient = 0.99). Our results suggest that OUES is applicable to adult cardiac patients as an objective, effort-independent estimation of cardiorespiratory functional reserve. Accepted: 7 September 1998     

Creatine supplementation alters the response to a graded cycle ergometer test

To determine the effects of creatine supplementation on cardiorespiratory responses during a graded exercise test (GXT) 36 trained adults (20 male, 16 female; 21–27 years old) performed two maximal GXTs on a cycle ergometer. The first GXT was done in a non-supplemented condition, and the second GXT was done following 7 days of ingesting either 5 g creatine monohydrate, encased in gelatin capsules, four times daily (CS, 13 male, 6 female), or the same number of glucose capsules (PL, 7 male, 10 female). CS significantly (P < 0.05) improved total test time [pre-CS=1217 (240) s, mean (std. dev.) versus post-CS=1289 (215) s], while PL administration had no effect (P > 0.05) on total test time [pre-PL=1037 (181) s versus post-PL=1047 (172) s]. In addition, both oxygen consumption (V˙ _O2) and heart rate at the end of each of the first five GXT stages were significantly lower after CS, but were unchanged after PL. Moreover, the ventilatory threshold occurred at a significantly greater V˙ _O2 for CS [pre-CS=2.2 (0.4) l · min⁻¹ or 66% of peak V˙ _O2 versus post-CS=2.6 (0.5) l · min⁻¹ or 78% of peak V˙ _O2; pre-PL=2.6 (0.9) l · min⁻¹ or 70% peak V˙ _O2 versus post-PL=2.6 (1.1) l · min⁻¹ or 68% of peak V˙ _O2]. Neither CS nor PL had an effect on peak V˙ _O2 [pre-CS=3.4 (0.7) l · min⁻¹ versus post-CS=3.3 (0.7) l · min⁻¹; pre-PL=3.7 (1.1) l · min⁻¹ versus post-PL=3.7 (1.1) l · min⁻¹]. Apparently, CS can alter the contributions of the different metabolic systems during the initial stages of a GXT. Thus, the body is able to perform the sub-maximal workloads at a lower oxygen cost with a concomitant reduction in the work performed by the cardiovascular system. Accepted: 20 April 2000     

Transient oxygen uptake response to exercise characterizes functional capacity of the cardiocirculatory system in patients with chronic heart failure: a random stimulus approach

The transient response of oxygen uptake (V˙O₂) to submaximal exercise, known to be abnormal in patients with cardiovascular disorders, can be useful in assessing the functional status of the cardiocirculatory system, however, a method for evaluating it accurately has not yet been established. As an alternative approach to the conventional test at constant exercise intensity, we applied a random stimulus technique that has been shown to provide relatively noise immune responses of system being investigated. In 27 patients with heart failure and 24 age-matched control subjects, we imposed cycle exercise at 50 W intermittently according to a pseudo-random binary (exercise-rest) sequence, while measuring breath-by-breath V˙O₂. After determining the transfer function relating exercise intensity (W˙) to V˙O₂ and attenuating the high frequency ranges (>6 exercise-rest cycles · min⁻¹), we computed the high resolution band-limited (0–6 cycles · min⁻¹) V˙O₂ response (0–120 s) to a hypothetical step exercise. The V˙O₂ response showed a longer time constant in the patients than in the control subjects [47 (SD 37) and 31 (SD 8) s, respectively, P < 0.05]. Furthermore, the amplitude of the V˙O₂ response after the initial response was shown to be significantly smaller in the patients than in the control subjects [176 (SD 50) and 267 (SD 54) ml · min⁻¹ at 120 s]. The average amplitude over 120 s correlated well with peak V˙O₂ (r = 0.73) and ΔV˙O₂/ΔW˙ (r = 0.70), both of which are well-established indexes of exercise tolerance. The data indicated that our band-limited V˙O₂ step response using random exercise was more markedly attenuated and delayed in the patients with heart failure than in the normal controls and that it could be useful in quantifying the overall functional status of the cardiocirculatory system. Accepted: 6 January 1998     

Specificity of treadmill and cycle ergometer tests in triathletes, runners and cyclists

The objective of this study was to evaluate the viability of using a single test in which cardiorespiratory variables are measured, to establish training guidelines in running and/or cycling training activities. Six triathletes (two females and four males), six runners (two females and four males) and six males cyclists, all with 5.5 years of serious training and still involved in racing, were tested on a treadmill and cycle ergometer. Cardiorespiratory variables [e.g., heart rate (HR), minute ventilation, carbon dioxide output (V˙CO₂)] were calculated relative to fixed percentages of maximal oxygen uptake (V˙O_2max; from 50 to 100%). The entire group of subjects had significantly (P < 0.05) higher values of V˙O_2max on the treadmill compared with the cycle ergometer [mean (SEM) 4.7 (0.8) and 4.4 (0.9) l · min⁻¹, respectively], and differences between tests averaged 10.5% for runners, 6.1% for triathletes and 2.8% for cyclists. A three-way analysis of variance using a 3 × 2 × 6 design (groups × tests × intensities) demonstrated that all factors yielded highly significant F-ratios (P < 0.05) for all variables between tests, even though differences in HR were only 4 beats · min⁻¹. When HR was plotted against a fixed percentage of V˙O_2max, a high correlation was found between tests. These results demonstrate that for triathletes, cyclists and runners, the relationship between HR and percentage of V˙O_2max, obtained in either a treadmill or a cycle ergometer test, may be used independently of absolute V˙O_2max to obtain reference HR values that can be used to monitor their running and/or cycling training bouts. Received: 3 November 1998 / Accepted: 29 July 1999     

Time to exhaustion during severe intensity running: response following a single bout of interval training

 The primary aim of this study was to examine any change in performance caused by a fatiguing interval training session (TS). A secondary aim of this study was to examine the change in oxygen uptake (V˙O₂) during moderate and severe intensity running, and the relationship with the change in performance. Seven male runners [mean age 24 (SD 6) years, height 1.79 (SD 0.06) m, body mass 67.9 (SD 7.6) kg, maximal oxygen uptake (V˙O_2max) 4.14 (SD 0.49) l · min⁻¹] were studied. The V˙O₂ during moderate and severe intensity running and running performance were studied immediately prior to, 1 h following, and 72 h following TS. The TS was performed on a treadmill, and consisted of six bouts of 800 m at 1 km · h⁻¹ below the velocity at V˙O_2max (v _V˙ O_2max), with 3-min rest intervals. Performance was also assessed at 1 km · h⁻¹ below v _V˙ O_2max, in the form of time to exhaustion (t _lim). The V˙O₂ and heart rate (f _c) were assessed both during the severe intensity performance trial, and the moderate intensity run at 50% v _V˙ O_2max. Whilst a significant change was observed in running performance and the V˙O₂ during both moderate and severe intensity running prior to and following TS, no relationship was observed between the magnitude of change in these variables. At 1 h following TS, t _lim had decreased by 24%, V˙O₂ during moderate intensity running had increased by 2%, and the difference in V˙O₂ between 2 min 45 s and the end of severe intensity running had increased by 91% compared with values recorded prior to TS. At 1 h following TS, ƒ_c had also increased significantly during moderate intensity running by 5% compared to the value recorded prior to TS. These findings demonstrated that TS resulted in a reduction in performance, and that the relationship between running performance and V˙O₂ during running may be altered under conditions of prolonged fatigue. Accepted: 16 September 1999     

Change in post-exercise vagal reactivation with exercise training and detraining in young men

We studied the effects of aerobic exercise training and detraining in humans on post-exercise vagal reactivation. Ten healthy untrained men trained for 8 weeks using a cycle ergometer [70% of initial maximal oxygen uptake ( ) for 1 h, 3–4 days·week^–1] and then did not exercise for the next 4 weeks. Post-exercise vagal reactivation was evaluated as the time constant of the beat-by-beat decrease in heart rate during the 30 s (t₃₀) immediately following 4 min exercise at 80% of ventilatory threshold (VT). The and the oxygen uptake at VT had significantly increased after the 8 weeks training programme (P<0.0001, P<0.001, respectively). The t₃₀ had shortened after training, and values after 4 weeks and 8 weeks of training were significantly shorter than the initial t₃₀ (P<0.05, P<0.01, respectively). The change in the t₃₀ after 8 weeks of training closely and inversely correlated with the initial t₃₀ (r=–0.965, P<0.0001). The reduced t₃₀ was prolonged significantly after 2 weeks of detraining, and had returned almost to the baseline level after a further 2 weeks of detraining. These results suggest that aerobic exercise training of moderate intensity accelerates post-exercise vagal reactivation, but that the accelerated function regresses within a few weeks of detraining. Electronic Publication     

In humans the oxygen uptake slow component is reduced by prior exercise of high as well as low intensity

The aim of the study was to examine to what extent prior high- or low-intensity cycling, yielding the same amount of external work, influenced the oxygen uptake (V˙O₂) slow component of subsequent high-intensity cycling. The 12 subjects cycled in two protocols consisting of an initial 3 min period of unloaded cycling followed by two periods of constant-load exercise separated by 3 min of rest and 3 min of unloaded cycling. In protocol 1 both periods of exercise consisted of 6 min cycling at a work rate corresponding to 90% peak oxygen uptake (V˙O_2peak). Protocol 2 differed from protocol 1 in that the first period of exercise consisted of a mean of 12.1 (SD 0.8) min cycling at a work rate corresponding to 50% V˙O_2peak. The difference between the 3rd min V˙O₂ and the end V˙O₂ (ΔV˙O₂₍₆₋₃₎) was used as an index of the V˙O₂ slow component. Prior high-intensity exercise significantly reduced ΔV˙O₂₍₆₋₃₎. The ΔV˙O₂₍₆₋₃₎ was also reduced by prior low-intensity exercise despite an unchanged plasma lactate concentration at the start of the second period of exercise. The reduction was more pronounced after prior high- than after prior low-intensity exercise (59% and 28%, respectively). The results of this study show that prior exercise of high as well as low intensity reduces the V˙O₂ slow component and indicate that a metabolic acidosis is not a necessary condition to elicit a reduction in ΔV˙O₂₍₆₋₃₎. Accepted: 8 July 2000     

The effect of nitrous oxide-induced narcosis on aerobic work performance

Previous findings of a narcosis-induced reduction in heat production during cold water immersion, as reflected in oxygen uptake (V˙O₂), have been attributed to the attenuation of the shivering response. The possibility of reduced oxygen utilization (V˙O₂) by the muscles could not, however, be excluded. Accordingly, the present study tested the hypothesis that mild narcosis, induced by inhalation of a normoxic gas mixture containing 30% nitrous oxide (N₂O), would affect V˙O₂. Nine male subjects participated in both maximal and submaximal exercise trials, inspiring either room air (AIR) or a normoxic mixture containing 30% N₂O. In the submaximal trials, the subjects exercised at 50% of maximal exercise intensity (W˙ _max ) as determined in the maximal AIR trial. Though the subjects attained the same W˙ _max in the AIR and N₂O trials, maximal V˙O₂ was significantly higher (P < 0.05) during the N₂O condition [58.9 (SEM 3.1) ml · kg^−1 ·min^−l] compared to the AIR condition [55.0 (SEM 2.4) ml · kg⁻¹ · min^−l]. However, the V˙O₂-relative exercise intensity relationship was similar during both maximal AIR and maximal N₂O at submaximal exercise intensities. There were no significant differences in the responses of oesophageal temperature, sweating rate, heart rate and ventilation between AIR and N₂O in the maximal and submaximal tests. It was concluded that the previously reported narcosis-induced reductions in V˙O₂ observed during cold water immersion can be attributed solely to a reduction in the shivering response rather than to decreased oxygen utilization by the muscles. Accepted: 6 February 2000     

Oxygen kinetics and modelling of time to exhaustion whilst running at various velocities at maximal oxygen uptake

The purpose of this study was to characterise the relationship between running velocity and the time for which a subject can run at maximal oxygen uptake (V˙O_{2 max}), (t _lim V˙O_{2 max}). Seven physical education students ran in an incremental test (3-min stages) to determine V˙O_{2 max} and the minimal velocity at which it was elicited (νV˙O_{2 max}). They then performed four all-out running tests on a 200-m indoor track every 2 days in random order. The mean times to exhaustion t _lim at 90%, 100%, 120% and 140% νV˙O_{2 max} were 13 min 22 s (SD 4 min 30 s), 5 min 47 s (SD 1 min 50 s), 2 min 11 s (SD 38 s) and 1 min 12 s (SD 18 s), respectively. Five subjects did not reach V˙O_{2 max} in the 90% νV˙O_{2 max} test. All the subjects reached V˙O_{2 max} in the runs at 100% νV˙O_{2 max}. All the subjects, except one, reached V˙O_{2 max} in the runs at 120%νV˙O_{2 max}. Four subjects did not reach V˙O_{2 max} in the 140% νV˙O_{2 max} test. Time to achieve V˙O_{2 max} was always about 50% of the time to exhaustion irrespective of the intensity. The time to exhaustion-velocity relationship was better fitted by a 3- than by a 2-parameter critical power model for running at 90%, 100%, 120%, 140% νV˙O_{2 max} as determined in the previous incremental test. In conclusion, t _lim V˙O_{2 max} depended on a balance between the time to attain V˙O_{2 max} and the time to exhaustion t _lim. The time to reach V˙O_{2 max} decreased as velocity increased. The t _lim V˙O_{2 max} was a bi-phasic function of velocity, with a peak at 100% νV˙O_{2 max}. Accepted: 2 February 2000     

The effect of training in male prepubertal and pubertal monozygotic twins

Nine male pairs of monozygotic twins aged 11–14 years, height 147 (7.6) cm and body mass 39.7 (9.6) kg, participated in this study. Twin zygocity was tested using morphological, dermatoglyphic and hematologic methods, and Tanner's five stages were used for the evaluation of biological maturation. One twin from each pair undertook training for 6 months, three times a week, with running at 85–120% of the lactate anaerobic threshold (LT). Anthropometrics, determination of maximum O₂ uptake (V˙O_2max), LT and maximal blood lactate concentration ([La]_max) was carried out before, during and after training. No significant difference existed between the trained twins and their untrained brothers before training. After training, the trained twins increased their V˙O_2max (per kg body mass) by 10.6% and their LT by 18.2% (P<0.01), reaching values that differed significantly from those of their untrained brothers [57.5 (3.6) ml·kg⁻¹·min⁻¹ vs 55.4 (3.3) ml·kg⁻¹·min⁻¹ and 13.4 (1.1) km·h⁻¹ vs 12.7 (1.1) km·h⁻¹, respectively]. In addition, in the trained twins relative body fat was reduced (P<0.05) from 17.8 to 16.2% and their somatotype altered significantly (decrease of endomorphy and mesomorphy and increase of ectomorphy), while in the untrained twins there was no change in these parameters. Both groups of twins significantly increased their absolute V˙O_2max after the 6 months of training, the trained by 14,9% [from 2.08 (0.43) to 2.37 (0.45) l·min⁻¹] and the untrained by 10.5% [from 2.10 (0.41) to 2.32 (0.47) l·min⁻¹], but no difference was registered between them. A comparison of the intrapair changes in V˙O_2max of prepubertal and pubertal twins showed an influence of training in the prepubertal (19.3% vs 5.2%) but not in the pubertal twins (12.7% vs 13.1%). Using analysis of variance, the relative importance of training, heredity and their interaction was evaluated to be 20%, 70% and 10%, respectively, for the change in body fat, 35%, 45% and 20%, respectively, for the change in relative V˙O_2max and 25–30%, 50–60% and 15–20%, respectively, for the change in LT. In conclusion, training during pubertal growth can favour aerobic power (depending on body composition) as well as aerobic capacity, but it has no effect on absolute V˙O_2max. Genetic control seems to have a strong effect on the extent of adaptations, and the genotype—training interaction explains a small, but prominent part of them. Electronic Publication     

Effects of glucose ingestion at the onset of moderate-intensity, prolonged exercise in women as compared to men

To test glucose tolerance during exercise, the effects of oral glucose ingestion (0.5 g · kg⁻¹) on plasma glucose and hormonal responses (insulin, catecholamines) were investigated in 11 women [mean (SEM) age 21.6 (1.3) years] and 10 men [22.0 (0.3) years] during cycle ergometer exercise (30 min at 60% maximum oxygen consumption, V˙O_2max). The two groups exhibited similar V˙O_2max values, when expressed per kg of lean body mass. Venous blood samples (5 ml) were withdrawn immediately before the exercise, during the exercise (at 3, 5, 10, 15 and 30 min) and at the 30th min of the recovery period. Glucose was ingested orally between the 2nd and the 3rd min of the exercise. As compared to men, plasma glucose concentrations were lower in women during exercise (P < 0.05 at 3, 15 and 30 min) and at the 30th min of the recovery period (P < 0.001), while plasma insulin concentrations were higher in women during exercise (P < 0.05 at 3, 15 and 30 min). The ratio of the area under the curve for glucose over the area under the curve for insulin was lower in women during exercise (P < 0.0002). A linear relationship between glucose and insulin concentrations was found only for women during exercise (r = 0.615, P < 0.0001). No gender difference was observed for the catecholamine concentration during exercise. In conclusion, this study postulates that an oral glucose load given at the onset of a prolonged and moderate exercise bout induced lesser plasma glucose and greater insulin concentrations in women as compared to men. These data argue in favour of a greater glucose tolerance in women during exercise. Accepted: 5 June 1999     

Neuromuscular adaptation during prolonged strength training, detraining and re-strength-training in middle-aged and elderly people

Effects of a 24-week strength training performed twice weekly (24 ST) (combined with explosive exercises) followed by either a 3-week detraining (3 DT) and a 21-week re-strength-training (21 RST) (experiment A) or by a 24-week detraining (24 DT) (experiment B) on neural activation of the agonist and antagonist leg extensors, muscle cross-sectional area (CSA) of the quadriceps femoris, maximal isometric and one repetition maximum (1-RM) strength and jumping (J) and walking (W) performances were examined. A group of middle-aged (M, 37–44 years, n=12) and elderly (E, 62–77, n=10) and another group of M (35–45, n=7) and E (63–78, n=7) served as subjects. In experiment A, the 1-RM increased substantially during 24 ST in M (27%, P < 0.001) and E (29%, P < 0.001) and in experiment B in M (29%, P < 0.001) and E (23%, P < 0.01). During 21 RST the 1-RM was increased by 5% at week 48 (P < 0.01) in M and 3% at week 41 in E (n.s., but P < 0.05 at week 34). In experiment A the integrated electromyogram (IEMG) of the vastus muscles in the 1-RM increased during 24 ST in both M (P < 0.05) and E (P < 0.001) and during 21 RST in M for the right (P < 0.05) and in E for both legs (P < 0.05). The biceps femoris co-activation during the 1-RM leg extension decreased during the first 8-week training in M (from 29 ± 5% to 25 ± 3%, n.s.) and especially in E (from 41 ± 11% to 32 ± 9%, P < 0.05). The CSA increased by 7% in M (P < 0.05) and by 7% in E (P < 0.001), and by 7% (n.s.) in M and by 3% in E (n.s.) during 24 ST periods. Increases of 18% (P < 0.001) and 12% (P < 0.05) in M and 22% (P < 0.001) and 26% (P < 0.05) in E occurred in J. W speed increased (P < 0.05) in both age groups. The only decrease during 3 DT was in maximal isometric force in M by 6% (P < 0.05) and by 4% (n.s.) in E. During 24 DT the CSA decreased in both age groups (P < 0.01), the 1-RM decreased by 6% (P < 0.05) in M and by 4% (P < 0.05) in E and isometric force by 12% (P < 0.001) in M and by 9% (P < 0.05) in E, respectively, while J and W remained unaltered. The strength gains were accompanied by increased maximal voluntary neural activation of the agonists in both age groups with reduced antagonist co-activation in the elderly during the initial training phases. Neural adaptation seemed to play a greater role than muscle hypertrophy. Short-term detraining led to only minor changes, while prolonged detraining resulted in muscle atrophy and decreased voluntary strength, but explosive jumping and walking actions in both age groups appeared to remain elevated for quite a long time by compensatory types of physical activities when performed on a regular basis. Accepted: 2 May 2000