Effect of electrical stimulation-induced muscle force and streptomycin treatment on muscle and trabecular bone mass in early-stage disuse musculoskeletal atrophy.

OBJECTIVES: The aim was to determine whether daily muscle electrical stimulation (ES) and streptomycin treatment would have positive or negative effects on trabecular bone mass in disuse rats. METHODS: Seven-week-old male F344 rats were randomly divided into five groups of eight animals each: an age-matched control group (CON); a sciatic denervation group (DN); a DN + direct electrical stimulation group (DN+ES); a DN + streptomycin treatment group (DN+SM); and a DN+ES+SM group. The tibialis anterior (TA) muscles in all ES groups were stimulated with 16mA at 10Hz for 30 min/day, six days/week, for one week. Bone volume and structure were evaluated using micro-CT, and histological examinations of the tibiae were performed. RESULTS: Direct ES significantly reduced the disuse-induced trabecular bone loss. Osteoid thickness were also significantly greater in the ES groups than in the DN group. Micro CT and histomorphological parameters were significantly lower in the DN+ES+SM group than in the DN+ES group, while there were no significant differences between the DN and DN+SM groups. CONCLUSIONS: These results suggest that ES-induced muscle force reduced trabecular bone loss, and streptomycin treatment did not induce bone loss, but attenuated the effects of ES-induced muscle force on reducing the loss of disused bone.

Electrical stimulation of denervated rat skeletal muscle retards trabecular bone loss in early stages of disuse musculoskeletal atrophy.

OBJECTIVES: We aimed to determine the intensity of muscle stimulation required to prevent structural failure as well as bone and skeletal muscle loss after denervation-induced disuse. METHODS: Seven-week-old rats (weight, 198-225 g) were randomly assigned to age-matched groups comprising control (CON), sciatic nerve denervation (DN) or direct electrical stimulation (ES) one day later [after denervation] with 4, 8 and 16 mA at 10 Hz for 30 min/day, six days/week, for one or three weeks. Bone architecture and mean osteoid thickness in histologically stained tibial sections and tension in tibialis anterior muscles were assessed at one and three weeks after denervation. RESULTS: Direct ES with 16 mA generated 23-30% maximal contraction force. Denervation significantly decreased trabecular bone volume fraction, thickness and number, connectivity density and increased trabecular separation in the DN group at weeks one and three. Osteoid thickness was significantly greater in the ES16 group at week one than in the DN and other ES groups. Trabecular bone volume significantly correlated with muscle weight. CONCLUSIONS: Relatively low-level muscle contraction induced by low-frequency, high-intensity electrical muscle stimulation delayed trabecular bone loss during the early stages (one week after DN) of musculoskeletal atrophy due to disuse.

Intra-abdominal pressure during swimming.

The present study aimed to determine the intra-abdominal pressure during front crawl swimming at different velocities in competitive swimmers and to clarify the relationships between stroke indices and changes in intra-abdominal pressure. The subjects were 7 highly trained competitive collegiate male swimmers. Intra-abdominal pressure was measured during front crawl swimming at 1.0, 1.2 and 1.4 m · s(-1) and during the Valsalva maneuver. Intra-abdominal pressure was taken as the difference between minimum and maximum values, and the mean of 6 stable front crawl stroke cycles was used. Stroke rate and stroke length were also measured as stroke indices. There were significant differences in stroke rate among all velocities (P < 0.05). However, there was no significant difference in stroke length by velocity. Significant within-subject correlations between intra-abdominal pressure and stroke rate or stroke length (P < 0.01) were observed, although there were no significant correlations between intra-abdominal pressure and stroke indices when controlling for swimming velocity. These findings do not appear to support the effectiveness of trunk training performed by competitive swimmers aimed at increasing intra-abdominal pressure.

Changes over time in structural plasticity of trabecular bone in rat tibiae immobilized by reversible sciatic denervation.

OBJECTIVE: The present study aimed to clarify the structural recovery, and to compare the time course of morphological changes in trabeculae and the process of bone mass change in rat tibiae following temporary immobilization of hind limb by sciatic neurectomy or nerve freezing. METHODS: In 11-week-old male Fischer 344 rats, 4-5 mm of the sciatic nerve was removed (neurectomy group) or frozen by 5-second application of a stainless steel rod immersed in liquid nitrogen (nerve-freezing group). Quantitative changes in cancellous bone were assessed by histomorphometry. RESULTS: The results clarified that: trabecular bone volume (BV/TV) decreases until 3 weeks after denervation, and in the nerve-freezing group, it then increases from week 4, recovering to pre-surgery levels by week 10 (no recovery was seen in the neurectomy group); in the initial phase of bone atrophy, the decrease in BV/TV is more gradual in the nerve-freezing group than in the neurectomy group; and changes in trabecular architecture in the bone atrophy-recovery process are strongly associated with changes in trabecular thickness. CONCLUSION: The findings suggested that after transient injury by nerve freezing and subsequent recovery of neuromuscular function, bone tissue undergoes recovery from bone loss, but that trabeculae may not show complete structural recovery.

Response training shortens visuo-motor related time in athletes.

In the present study, we aimed to determine whether response training shortens visuo-motor related time in athletes performing a simple reaction task. 14 healthy male athletes were included in the study. Subjects were randomly divided into 2 groups: a training group, which underwent response training consisting of a mastication task in response to a visual signal, and a non-training (control) group, which did not undergo response training. Pre-motor time and transcranial magnetic stimulation over the primary motor cortex for recording motor evoked potentials were measured in the control group, and before and after the response training session in the training group. Both pre-motor time and visuo-motor related time, but not motor evoked potential latency, were significantly reduced after response training in the training group. Subjects who had a longer visuo-motor related time before training showed a greater reduction in visuo-motor related time after training. These results suggest that visuo-motor related time before training could be useful as a predictor of the reduction in reaction time following response training.

Sequential expression of vascular endothelial growth factor, Flt-1, and KDR/Flk-1 in regenerating mouse skeletal muscle.

We investigated the expression of vascular endothelial growth factor (VEGF) and its receptors (Flt-1 and KDR/Flk-1) during muscle regeneration by immunohistochemistry and real-time RT-PCR. On days 5 and 7 after the induction of injury, VEGF and Flt-1 were detected in the cytoplasm and KDR/Flk-1 in the cytoplasm and on cell membranes of the same regenerating muscle fibers. The levels of these proteins in the regenerating muscle fibers gradually decreased until day 20. In contrast, these proteins were not detected in the fibers of normal muscle. This suggests that regenerating muscle fibers express VEGF and its receptors in response to injury. In addition, we found that the VEGF mRNA transcript transiently increased after 12 h of muscle injury and then returned to the basal levels observed in normal muscles on day 1. The expression of Flt-1 and KDR/Flk-1 mRNA transcripts also peaked on day 3 and then returned to the basal levels observed in normal muscles on day 10. These findings suggest that regenerating muscle fibers are an important source of VEGF and that VEGF signaling through Flt-1 and KDR/Flk-1 may be involved in the process of muscle regeneration in vivo.

Effect of low blood glucose on plasma CRF, ACTH, and cortisol during prolonged physical exercise.

The effects of low blood glucose concentration during low-intensity prolonged physical exercise on the hypothalamus-pituitary-adrenocortical axis were investigated in healthy young men. In experiment 1, six subjects who had fasted for 14 h performed bicycle exercise at 50% of their maximal O2 uptake until exhaustion. At the end of the exercise, adrenocorticotropic hormone (ACTH) and cortisol increased significantly. However, this hormonal response was totally abolished when the same subjects exercised at the same intensity while blood glucose concentrations were maintained at the preexercise level. In experiment 2, in addition to ACTH and cortisol, the possible changes in plasma concentration of corticotropin-releasing factor (CRF) were investigated during exercise of the same intensity performed by six subjects. As suggested by a previous study (Tabata et al. Clin. Physiol. Oxf. 4: 299-307, 1984), when the blood glucose concentrations decreased to less than 3.3 mM, plasma concentrations of CRF, ACTH, and cortisol showed a significant increase. At exhaustion, further increases were observed in plasma CRF, ACTH, and cortisol concentrations. These results demonstrate that decreases in blood glucose concentration trigger the pituitary-adrenocortical axis to enhance secretion of ACTH and cortisol during low-intensity prolonged exercise in humans. The data also might suggest that this activation is due to increased concentration of CRF, which was shown to increase when blood glucose concentration decreased to a critical level of 3.3 mM.

Effect of hand paddles on anaerobic energy release during supramaximal swimming.

PURPOSE: Swimmers swim faster using hand paddles. In this study the effect of maximal performance using hand paddles on aerobic and anaerobic energy release during supramaximal swimming was examined by comparing the maximal accumulated O2 deficit, and the aerobic and anaerobic energy release during exhaustive swimming with paddles (P) to swimming without paddles (hands only, H). METHODS: The subjects were six trained college male swimmers. Experiments were carried out in a swimming flume. The water flow rate was set before each exercise bout such that exhaustion occurred in 30 s, 1 min, or 2-3 min. Accumulated O2 deficit during exercise was determined by the accumulated oxygen demand minus the accumulated O2 uptake. RESULTS: Water flow rates at which maximal accumulated O2 deficit was obtained were significantly higher in P than that in H. However, mean values of maximal accumulated O2 deficit during H and P were 2.40+/-0.42 L and 2.32+/-0.37 L, respectively, and there was no significant difference between these two values. Furthermore, during the supramaximal swimming to exhaustion in 30 s, 1 min, or 2-3 min, both accumulated O2 uptake and accumulated O2 deficit did not significantly differ between these conditions, although mean water flow rates of these supramaximal swimming bouts were significantly higher in P than those in H again. CONCLUSIONS: These results suggest that the faster swimming speed accomplished with hand paddles does not affect metabolic responses and that it may be realized by recruitment of roughly the same muscle mass. Therefore, the ability to swim faster with hand paddles might mainly be attributed to other than metabolic factors, i.e., a higher propelling efficiency.

Simulated front crawl swimming performance related to critical speed and critical power.

PURPOSE: Competitive pool swimming events range in distance from 50 to 1500 m. Given the difference in performance times (+/- 23-1000 s), the contribution of the aerobic and anaerobic energy systems changes considerably with race distance. In training practice the regression line between swimming distance and time (Distance = critical velocity x time + anaerobic swimming capacity) is used to determine the individual capacity of the aerobic and anaerobic metabolic pathways. Although there is confidence that critical velocity and anaerobic swimming capacity are fitness measures that separate aerobic and anaerobic components, a firm theoretical basis for the interpretation of these results does not exist. The purpose of this study was to evaluate the critical power concept and anaerobic swimming capacity as measures of the aerobic and anaerobic capacity using a modeling approach. METHODS: A systems model was developed that relates the mechanics and energetics involved in front crawl swimming performance. From actual swimming flume measurements, the time dependent aerobic and anaerobic energy release was modeled. Data derived from the literature were used to relate the energy cost of front crawl swimming to swimming velocity. A balance should exist between the energy cost to swim a distance in a certain time and the concomitant aerobic and anaerobic energy release. The ensuing model was used to predict performance times over a range of distances (50-1500 m) and to calculate the regression line between swimming distance and time. RESULTS AND CONCLUSIONS: Using a sensitivity analysis, it was demonstrated that the critical velocity is indicative for the capacity of the aerobic energy system. Estimates of the anaerobic swimming capacity, however, were influenced by variations in both anaerobic and aerobic energy release. Therefore, it was concluded that the anaerobic swimming capacity does not provide a reliable estimate of the anaerobic capacity.

Metabolic profile of high intensity intermittent exercises.

To evaluate the magnitude of the stress on the aerobic and the anaerobic energy release systems during high intensity bicycle training, two commonly used protocols (IE1 and IE2) were examined during bicycling. IE1 consisted of one set of 6-7 bouts of 20-s exercise at an intensity of approximately 170% of the subject's maximal oxygen uptake (VO2max) with a 10-s rest between each bout. IE2 involved one set of 4-5 bouts of 30-s exercise at an intensity of approximately 200% of the subject's VO2max and a 2-min rest between each bout. The accumulated oxygen deficit of IE1 (69 +/- 8 ml.kg-1, mean +/- SD) was significantly higher than that of IE2 (46 +/- 12 ml.kg-1, N = 9, p < 0.01). The accumulated oxygen deficit of IE1 was not significantly different from the maximal accumulated oxygen deficit (the anaerobic capacity) of the subjects (69 +/- 10 ml.kg-1), whereas the corresponding value for IE2 was less than the subjects' maximal accumulated oxygen deficit (P < 0.01). The peak oxygen uptake during the last 10 s of the IE1 (55 +/- 6 ml.kg-1.min-1) was not significantly less than the VO2max of the subjects (57 +/- 6 ml.kg-1.min-1). The peak oxygen uptake during the last 10 s of IE2 (47 +/- 8 ml.kg-1.min-1) was lower than the VO2max (P < 0.01). In conclusion, this study showed that intermittent exercise defined by the IE1 protocol may tax both the anaerobic and aerobic energy releasing systems almost maximally.

Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max.

This study consists of two training experiments using a mechanically braked cycle ergometer. First, the effect of 6 wk of moderate-intensity endurance training (intensity: 70% of maximal oxygen uptake (VO2max), 60 min.d-1, 5 d.wk-1) on the anaerobic capacity (the maximal accumulated oxygen deficit) and VO2max was evaluated. After the training, the anaerobic capacity did not increase significantly (P > 0.10), while VO2max increased from 53 +/- 5 ml.kg-1 min-1 to 58 +/- 3 ml.kg-1.min-1 (P < 0.01) (mean +/- SD). Second, to quantify the effect of high-intensity intermittent training on energy release, seven subjects performed an intermittent training exercise 5 d.wk-1 for 6 wk. The exhaustive intermittent training consisted of seven to eight sets of 20-s exercise at an intensity of about 170% of VO2max with a 10-s rest between each bout. After the training period, VO2max increased by 7 ml.kg-1.min-1, while the anaerobic capacity increased by 28%. In conclusion, this study showed that moderate-intensity aerobic training that improves the maximal aerobic power does not change anaerobic capacity and that adequate high-intensity intermittent training may improve both anaerobic and aerobic energy supplying systems significantly, probably through imposing intensive stimuli on both systems.

Oxygen uptake in one-legged and two-legged exercise.

PURPOSE: The purpose of this study was to determine the primary factors causing the differential oxygen uptake (VO2) response at submaximal intensities between one-legged and two-legged exercise, and whether peak oxygen uptake (VO2peak) increases in proportion to the increase in active muscle mass. METHODS: Two different types of exercise were used for this experiment, each requiring a different movement, a different method of stabilizing posture, and, finally, a different limiting VO2peak. In experiment 1, nine male subjects performed one-legged cycling (OLC) and two-legged cycling exercise (TLC) at a pedaling rate of 80 rpm. The exercise intensity was first set at 80 W and was increased by 40 W every 3 min until exhaustion. In experiment 2, six healthy male subjects performed one-legged knee-extension (OKE) and two-legged knee-extension (TKE) exercise at a rate of 50 contractions per minute. The knee-extension exercise was done at constant work rates for a 3-min session in OKE or a 4-min session in TKE. The exercise bouts were performed intermittently at four to seven different submaximal intensities and VO2 was determined at each intensity in all exercises. RESULTS: At submaximal intensities, VO2 in relation to work rate of one-legged exercise was more steep than those of two-legged exercise, and the mean values of VO2 were significantly higher in one-legged exercise than those in two-legged exercise in both knee extension and cycling exercise. Mean values of VO2peak for two-legged exercise were significantly higher than that for one-legged exercise (P < 0.01); however, it was much lower than two times of that for one-legged exercise even in knee extension exercise where the VO2peak would be limited peripherally. CONCLUSION: The findings of this study suggest that the differential VO2 response between one-legged and two-legged exercise would be attributed not only to the difference in force application throughout the exercise movement and to the effect of a postural component but also to the inhibited circulatory response caused by the multiple limb exercise. In addition, it was supposed that VO2peak does not increase in proportion to the exercising muscle mass even during smaller muscle activity where the cardiac pumping capacity has not reached its upper limit.

Cardiovascular drift during low intensity exercise with leg blood flow restriction.

Previous studies reported that aerobic-type exercise such as walking or cycling with blood flow restriction (BFR) has been shown to elicit increases in leg muscle hypertrophy and strength, as well as improved aerobic capacity. Although previous studies investigated cardiovascular responses during a relatively short duration of exercise (∼5 min), the effects of prolonged leg muscular BFR have remained unknown. The purpose of this study was to examine the cardiovascular effects of longer duration low intensity exercise combined with BFR. Eight men performed 30 min of exercise at 40% of a predetermined maximal oxygen uptake under both BFR and normal flow (CON) conditions. Cardiovascular parameters were measured at rest and every 10 min during exercise. The main findings were that 1) the SV and HR did not change significantly between 10 to 30 min of exercise in BFR and CON conditions, although BFR-induced reduction of SV and increased HR were found at 10 min exercise compared with normal flow, 2) blood pressure was increased at 10 min of exercise in BFR compared to the CON, however the blood pressure decreased gradually with BFR from 10 to 30 min of exercise, and 3) blood lactate and RPE increased gradually during exercise with BFR. In conclusion, our results suggest that the BFR-induced reduction of SV and increased HR within the first 10 min of exercise are representative of changes in these parameters.

Capillary supply and gene expression of angiogenesis-related factors in murine skeletal muscle following denervation.

Capillary supply of skeletal muscle decreases during denervation. To gain insight into the regulation of this process, we investigated capillary supply and gene expression of angiogenesis-related factors in mouse gastrocnemius muscle following denervation for 4 months. Frozen transverse sections were stained for alkaline phosphatase to detect endogenous enzyme in the capillary endothelium. The mRNA for angiogenesis-related factors, including hypoxia inducible factor-1alpha (HIF-1alpha), vascular endothelial growth factor (VEGF), kinase insert domain-containing receptor/fetal liver kinase-1 (KDR/Flk-1), fms-like tyrosine kinase (Flt-1), angiopoietin-1 and tyrosine kinase with Ig and epidermal growth factor(EGF) homology domain 2 (Tie-2), was analysed using a semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). The fibre cross-sectional area after denervation was about 20% of the control value, and the capillary to fibre ratio was significantly lower in denervated than in control muscles. The number of capillaries around each fibre also decreased to about 40% of the control value. These observations suggest that muscle capillarity decreases in response to chronic denervation. RT-PCR analysis showed that the expression of VEGF mRNA was lower in denervated than in control muscles, while the expression of HIF-1alpha mRNA remained unchanged. The expression levels of the KDR/Flk-1 and Flt-1 genes were decreased in the denervated muscle. The expression levels of angiopoietin-1 but not Tie-2 genes were decreased in the denervated muscle. These findings indicate that reduction in the expression of mRNAs in the VEGF/KDR/Flk-1 and Flt-1 as well as angiopoietin-1/Tie-2 signal pathways might be one of the reasons for the capillary regression during chronic denervation.

Oxygen uptake during swimming in a hypobaric hypoxic environment.

The purpose of this study was to determine oxygen uptake (VO2) at various water flow rates and maximal oxygen uptake (VO2max) during swimming in a hypobaric hypoxic environment. Seven trained swimmers swam in normal [N; 751 mmHg (100.1 kPa)] and hypobaric hypoxic [H; 601 mmHg (80.27 kPa)] environments in a chamber where atmospheric pressure could be regulated. Water flow rate started at 0.80 m.s-1 and was increased by 0.05 m.s-1 every 2 min up to 1.00 m.s-1 and then by 0.05 m.s-1 every minute until exhaustion. At submaximal water flow rates, carbon dioxide production (VCO2), pulmonary ventilation (VE) and tidal volume (VT) were significantly greater in H than in N. There were no significant differences in the response of submaximal VO2, heart rate (fc) or respiratory frequency (fR) between N and H. Maximal VE, fR, VT, fc, blood lactate concentration and water flow rate were not significantly different between N and H. However, VO2max under H [3.65 (SD 0.11) l.min-1] was significantly lower by 12.0% (SD 3.4)% than that in N [4.15 (SD 0.18) l.min-1]. This decrease agrees well with previous investigations that have studied centrally limited exercise, such as running and cycling, under similar levels of hypoxia.

Blood flow during muscle contraction and relaxation in rhythmic exercise at different intensities.

Effect of contraction force on blood flow during the contraction and relaxation phase of rhythmic handgrip exercise was studied on 6 healthy women. Velocity of blood flow in the brachial artery and the diameter of the artery were studied by Doppler-ultrasound method. Both the peak and mean velocity of the blood flow were significantly higher during the relaxation period than during contraction, and the velocity during the relaxation period was significantly higher in 30% MVC exercise than in 10% MVC exercise. However, no significant differences were found in the diameter of the artery between resting and exercise conditions, nor between exercises at different intensities. Thus blood flow during the relaxation phase was significantly increased from 135.7 +/- 18.2 ml.min-1 (10% MVC) to 182.5 +/- 19.6 ml.min-1 (30% MVC) by an increased contraction force, whereas blood flow during the contraction phase was hardly affected by increased contraction force.

Peak oxygen uptake during arm stroke under a hypobaric hypoxic condition.

The purpose of this study was to examine the limiting factor for swimming by measuring peak oxygen uptake (peak VO2) during front crawl (C) and arm stroke (A) under a hypobaric hypoxic condition. Seven-trained swimmers (age; 19-21 yrs, 100 m free style event; 57.2 +/- 2.5 secs) were measured twice under a normal (N) (751 mmHg) and a hypobaric hypoxic (H) (602 mmHg) condition in a chamber where atmospheric pressure was regulated. Water flow rate started at 0.80 m.sec-1 and was increased by 0.05 m.sec-1 every 2 min up to 1.00 m.sec-1. Subsequently, flow rate was increased by 0.05 m.sec-1 every minute until exhaustion. VO2 was measured with an automatic analyzer. The peak heart rate under N was not significantly different from that under H in both C (N; 190 +/- 9, H; 184 +/- 6 beats.min-1) and A (N; 180 +/- 6, H; 181 +/- 6 beats.min-1). Peak VO2 values during A (N; 3.42 +/- 0.27, H; 3.08 +/- 0.19 l.min-1) were significantly lower by 15-20% than those during C (N; 4.18 +/- 0.18, H; 3.65 +/- 0.11 l.min-1) for both N and H (p less than 0.01). Peak VO2 values under H were significantly lower than those under N during both C and A (p less than 0.01). There was no significant difference in the magnitude of decrease in peak VO2 between C (12.0 +/- 3.4%) and A (9.8 +/- 3.8%) under H. This ratio of decrease agrees with previous investigations that studied centrally limited exercise, such as running and cycling, under similar levels of hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential cardiorespiratory response to combined exercise with different combinations of forearm and calf exercise.

The purpose of this study was to examine whether cardiorespiratory responses to combined rhythmic exercise (60 contractions.min-1) was affected by different combinations of upper and lower limb exercise in seven healthy women. Six different rhythmic exercises were compared: 6-min rhythmic handgrip at 10% of isometric maximal voluntary contraction (MVC) (H10); 6-min rhythmic plantar flexion at 10% MVC (P10); exhausting rhythmic handgrip at 50% MVC (H50); exhausting rhythmic plantar flexion at 50% MVC (P50); H50 was added to P10 (P10H50); and P50 was added to H10 (H10P50). Exercise duration, after handgrip was combined with plantar flexion (P10H50), was shorter than that of H50, although the exercise duration of H10P50 was not significantly different from P50. No significant difference was found between the difference from rest in oxygen uptake (delta VO2) during H10P50 and the sum of delta VO2 during H10 and P50. Also, the differences from rest in forearm blood flow (delta FBF) and calf blood flow (delta CBF) during H10P50 were not significantly different from delta FBF in H10 and from delta CBF in P50. In contrast, delta VO2 in P10H50 was lower than the sum of delta VO2 in P10 and H50 (P < 0.05), and delta FBF in P10H50 was lower than that in H50 (P < 0.05), while delta CBF was not significantly different between P10H50 and P10. The changes in heart rate from rest (delta HR) during the combined exercises were lower than the sums of delta HR in the corresponding single exercises (P < 0.05). These results demonstrated an inhibitory summation of several cardiorespiratory responses to combined exercise resulting in a reduction in exercise performance which would seem to occur easily when upperlimb exercise is added to lower limb exercise.

Effect of hand paddle aids on oxygen uptake during arm-stroke-only swimming.

Cardiorespiratory responses during arm-stroke-only swimming with and without the aid of paddle were compared in seven trained swimmers. Water flow rate was started at 0.80 m.s-1 and was increased by 0.05 m.s-1 every 2 min up. to 1.00 m.s-1. Subsequently, the flow rate was increased by 0.05 m.s-1 every minute until exhaustion. At given submaximal water flow rates, oxygen uptake, heart rate (fc), pulmonary ventilation (VE) and respiratory frequency (fR) during swimming using hands alone (H) were significantly higher than when aided by paddles (P). There were no significant differences in tidal volume (VT) between H and P. The subjects were able to swim significantly faster using paddles (P < 0.05); however, no significant differences between H and P were found in peak oxygen uptake (VO2peak, Fc, VE, FR, VT and the blood lactate concentration at which VO2peak was obtained (P > 0.05). These results would suggest that the ability to swim faster with paddles does not depend on higher energy production but may be attributed to higher propelling efficiency.

The comparison of peak oxygen uptake between swim-bench exercise and arm stroke.

To compare maximal cardio-respiratory stress between swim-bench exercise (SB) and arm stroke (AS), peak oxygen uptake (VO2peak) was measured in six trained swimmers. The SB was performed at stroke frequency of 50.min-1. Oxygen uptake (VO2) was measured during exercise at 3-min constant exercise intensities in SB and at 4-min constant water flow rates in AS. We measured a steady-state VO2 within 3 or 4 min after the beginning of each exercise. The exercise intensity or the water flow rate was increased by 14.7 W or by 0.05 m.s-1, respectively, until a levelling-off of VO2 was observed. The VO2 was measured by the Douglas bag method. Heart rate (HR) and blood lactate concentration ([la-]b) were determined at the exercise intensity and the water flow rate at which VO2peak was obtained. At submaximal levels, VO2 increased in proportion to exercise intensity for SB and to the water flow rate for AS. A levelling-off of VO2 was observed in all subjects for both kinds of exercise. The VO2peak during SB [2.13 (SD 0.25)1.min-1] was significantly lower than that during AS [2.72 (SD 0.39)1.min-1] and corresponded to 78.9 (SD 7.0)% of AS VO2peak. Maximal HR during SB was also significantly lower than that during AS. No significant differences between SB and AS were found for either pulmonary ventilation or [la-]b. The peak exercise duration in SB [2.4 (SD 0.5) min] was significantly shorter than that in As [3.6 (SD 0.5) min]. These results would suggest that even though both kinds of exercise use the muscles of the upper body, active muscle groups involved during SB are different and/or smaller, and maximal stress on the cardio-respiratory system is lower when compared to AS.