Cardiac output in paraplegic subjects at high exercise intensities

Summary The purpose of this investigation was to compare cardiac output ( _c ) in paraplegic subjects (P) with wheelchair-confined control subjects (C) at high intensities of arm exercise. At low and moderate exercise intensity _c was the same at a given oxygen uptake ( O₂) in P and C. A group of 11 athletic male P with complete spinal-cord lesions between T6 and T12 and a group of 5 well-matched athletic male C performed maximal arm-cranking exercise and submaximal exercise at 50%, 70% and 80% of each individual's maximal power output (W_max) . Maximal O₂ ( O_2max) was significantly lower, O_2max per kilogram body mass was equal and maximal heart rate (f _c) was significantly higher in P compared to C. At O₂ of 1.3, 1.5 and 1.7 1-min^–1, and for P 65%–90% of the O_2max, _c was not significantly different between the groups, although, _c in P was achieved with a significantly lower stroke volume (SV) and a significantly higherf _c. Although the SV was lower in P, it followed the same pattern as SV in C during incremental exercise, i.e. an increase in SV until about 45%W _max and thereafter a stable SV. The similar _c at a given O₂ in both groups indicated that, even at high exercise intensities, circulation in P can be considered isokinetic with a complete compensation byf _c for a lower SV.     

Cardiovascular responses of cardiac transplant patients to arm and leg exercise

This investigation compares the cardiovascular responses of normal (n=10) and cardiac transplant (n=14) subjects to peak arm and leg exercise. It also tests the hypothesis that the higher heart rate (f _c) in normal subjects during light (30 W) submaximal arm versus leg exercise is due to cardiac innervation. In cardiac transplant patients, power output, oxygen consumption ,f _c and rate pressure product were 54%, 28%, 7%, and 8% lower during peak arm than leg exercise, respectively. In normal subjects, power output, ,f _c and rate pressure product were 61%, 33%, 8%, and 11% lower during peak arm than leg exercise, respectively. In cardiac transplant patients there was no significant difference in absolutef _c during submaximal arm and leg exercise. In normal subjects, absolutef _c during arm and leg exercise was [mean (SD)] 97 (4) beats · min^–1 and 92 (4) beats · min^–1, respectively (P=0.07). Plasma noradrenaline was increased more during arm than leg exercise in both cardiac transplant and normal subjects. Maximal leg testing is useful when determining the capacity of cardiac transplant patients to perform arm work. The higher absolutef _c reported by other investigators for normal subjects during submaximal arm versus leg exercise may be mediated by cardiac innervation.     

Cardiovascular responses to sustained maximal isometric contractions of the finger flexors

Summary This study investigated cardiovascular responses to 2 min sustained submaximal (20% MVC) and maximal (100% MVC) voluntary isometric contractions of the finger flexors in healthy young women. Cardiovascular variables investigated were: heart rate (f _c), mean arterial pressure ( _a), and stroke volume (SV). Doppler echocardiography was used to estimate SV from measures of aortic diameter (AD) and time-velocity integrals. Preliminary studies indicated that AD did not change significantly after 2 min sustained 100% MVC. Therefore, pre-exercise AD values were used to calculate SV before, during and after exercise. During the 2-min 100% MVC period, f _c and _aincreased significantly during the first 30 s of contraction. f _c then remained constant during the remainder of the 2-min contraction period, while _acontinued to rise. SV did not change significantly during the 100% MVC task but increased significantly during recovery from sustained 100% MVC. The data suggest that the magnitude of cardiovascular responses to isometric exercise is dependent on the specific task performed, and that there is a different pattern of response for f _c, _a, and SV during 20% and 100% MVC tasks. Unlike f _c and _a, SV did not change significantly during isometric exercise, but increased significantly after sustained 100% MVC.     

Cardiac output during exercise in paraplegic subjects

Summary The purpose of this study was to measure the cardiac output using the CO₂ rebreathing method during submaximal and maximal arm cranking exercise in six male paraplegic subjects with a high level of spinal cord injury (HP). They were compared with eight able bodied subjects (AB) who were not trained in arm exercise. Maximal O₂ consumption ( O_2max) was lower in HP (1.1 1·min^–1, SD 0.1; 17.5 ml·min^–·kg, SD 4) than in AB (2.5 1·min^–1, SD 0.6; 36.7 ml·min^–1·kg, SD 10.7). Maximal cardiac output was similar in the groups (HP, 141·min^–1 SD 2.6; AB, 16.81·min^–1 SD 4). The same result was obtained for maximal heart rate (f _c,max (HP, 175 beats·min^–1, SD 18; AB, 187 beats·min^–, SD 16) and the maximal stroke volume (HP, 82 ml, SD 13; AB, 91 ml, SD 27). The slopes of the relationshipf _c/ O₂ were higher in HP than AB (P<0.025) but when expressed as a % O_2max there were no differences. The results suggests a major alteration of oxygen transport capacity to active muscle mass in paraplegics due to changes in vasomotor regulation below the level of the lesion.     

Cardiovascular response to static handgrip in trained and untrained men

Summary The influence of aerobic capacity on the cardiovascular response to handgrip exercise, in relation to the muscle mass involved in the effort, was tested in 8 trained men (T) and 17 untrained men (U). The subjects performed handgrip exercises with the right-hand (RH), left-hand (LH) and both hands simultaneously (RLH) at an intensity of 25% of maximal voluntary contraction force. Maximal aerobic capacity was 4.3 l·min^–1 in T and 3.21·min^–1 in U (P<0.01). The endurance time for handgrip was longer in T than in U by 29% (P<0.05) for RH, 38% (P<0.001) for LH and 24% (P<0.001) for RLH. Heart rate (f _c) was significantly lower in T than in U before handgrip exercise, and showed smaller increases (P<0.01) at the point of exhaustion: 89 vs 106 beats·min^–1 for RH, 93 vs 100 beats·min^–1 for LH and 92 vs 108 beats·min^–1 for RLH. Stroke volume (SV) at rest was greater in T than in U and decreased significantly (P<0.05) during handgrip exercise in both groups of subjects. At the point of exhaustion SV was still greater in T than in U: 75 vs 57 ml for RH, 76 vs 54 ml for LH and 76 vs 56 ml for RLH. During the last seconds of handgrip exercise, the left ventricular ejection time was longer in T than in U. Increases in cardiac output (Q _c) and systolic blood pressure did not differ substantially between T and U, nor between the handgrip exercise tests. It was concluded that handgrip exercise caused similar increases inQ _c in both T and U but in T the increased level ofQ _c was an effect of greater SV and lowerf _c than in U. Doubling the muscle mass did not alter the cardiovascular response to handgrip exercise in either T or U.     

Kinetics of cardiorespiratory response to dynamic and rhythmic — static exercise in men

Summary Kinetics of cardiorespiratory response to dynamic (DE) and then to rhythmic-static exercise (RSE) was compared in nine male subjects exercising in an upright position on a cycle ergometer at an intensity of about 50 % O_2max and a mean pedalling frequency of 60 rpm over 5 min. Respiratory frequency (f _R), tidal volume (V _T), minute ventilation ( _E), heart rate (f _c), stroke volume (SV), and cardiac output (Q _t) were measured continuously. The RSE caused a greater increase in f _R than DE, whereas V _T increased more during DE. The effect of reciprocal changes in f _R and V _T was that _E and its kinetics, expressed as a time constant (), did not differ between experimental situations. The ventilatory equivalent for O₂ ( _E: O₂) was greater for RSE (31.3) than for DE (23.0, P<0.01). Elevation of f _c was similar for both types of exercise. The SV increased suddenly at the beginning of DE from 54 ml to 74 ml and then decreased to the end of exercise. At the onset of RSE only a moderate increase in SV was observed, from 56 ml to 62 ml, and then SV remained stable. The DE caused a greater and faster increase in Q _t (4.20 l · min^–1, for equal to 16.1s) than RSE (3.25 l · min^–1, for equal to 57.0s, P<0.05 and P<0.002, respectively). Total peripheral resistance was almost 40% greater for RSE than for DE. No relationship was found between Q _t and V_E at the first 15 s of both types of exercise. It is concluded that the kinetics of _E did not depend on to kinetics of Q _t in the exercising subjects. This finding contradicts the hypothesis of cardiodynamic hyperpnoea indicating an importance of neurogenic factors, mediated either centrally or peripherally, in fast cardiorespiratory responses to exercise.     

Cardiovascular responses at the onset of passive leg cycle exercise in paraplegics with spinal cord injury

The purpose of this study was to examine the cardiovascular responses at the onset of passive leg cycle exercise (PLCE) in paraplegics with spinal cord injury (PSCI) to investigate the increase in venous return from the paralyzed lower limbs during PLCE. Six male PSCI having lesions at levels ranging from T8 to L1 and five male able-bodied subjects (ABS) participated in this study. The subjects performed PLCE at pedalling frequencies of 40 rpm for 6 min. Cardiac output (Q˙ _c), stroke volume (SV) and heart rate (f _c) were measured before and during PLCE. In the steady state (4th and 5th min) of PLCE, both PSCI and ABS showed a significant increase in Q˙ _c. At the onset of PLCE, however, clear differences in the cardiovascular response were found between PSCI and ABS. The ABS showed a rapid and marked increase in f _c and consequently Q˙ _c within 20 s of the onset of PLCE. On the other hand, in PSCI, the Q˙ _c increased more slowly, compared with that in ABS, because of a smaller increase in f _c and a delayed increase in SV. The observed delay in the increases of Q˙ _c and SV at the onset of PLCE in PSCI was presumably due to the absence of afferent reflexes from the lower limbs, and to the additional time needed for venous return to arrive at the heart from the passively moved muscles. Accepted: 23 September 1999     

Endurance training slows down the kinetics of heart rate increase in the transition from moderate to heavier submaximal exercise intensities

Summary To find out whether endurance training influences the kinetics of the increases in heart rate (f _c) during exercise driven by the sympathetic nervous system, the changes in the rate off _c adjustment to step increments in exercise intensities from 100 to 150 W were followed in seven healthy, previously sedentary men, subjected to 10-week training. The training programme consisted of 30-min cycle exercise at 50%–70% of maximal oxygen uptake ( O_2max) three times a week. Every week during the first 5 weeks of training, and then after the 10th week the subjects underwent the submaximal three-stage exercise test (50, 100 and 150 W) with continuousf _c recording. At the completion of the training programme, the subjects' O_2max had increased significantly(39.2 ml·min^–1·kg^–1, SD 4.7 vs 46 ml·min^–1·kg^–1, SD 5.6) and the steady-statef _c at rest and at all submaximal intensities were significantly reduced. The greatest decrease in steady-statef _c was found at 150 W (146 beats·min^–1, SD 10 vs 169 beats·min^–1, SD 9) but the difference between the steady-statef _c at 150 W and that at 100 W (f _c) did not decrease significantly (26 beats·min^–1, SD 7 vs 32 beats·min^–1, SD 6). The time constant () of thef _c increase from the steady-state at 100 W to steady-state at 150 W increased during training from 99.4 s, SD 6.6 to 123.7 s, SD 22.7 (P<0.01) and the acceleration index (A=0.63·f _c·^–1) decreased from 0.20 beats·min^–1·s^–1, SD 0.05 to 0.14 beats·min^–1·s^–1, SD 0.04 (P<0.02). The major part of the changes in and A occurred during the first 4 weeks of training. It was concluded that heart acceleration following incremental exercise intensities slowed down in the early phase of endurance training, most probably due to diminished sympathetic activation.     

Early adaptations in gas exchange,cardiac function and haematology to prolonged exercise training in man

Summary In order to determine the effect of shortterm training on central adaptations, gas exchange and cardiac function were measured during a prolonged submaximal exercise challenge prior to and following 10–12 consecutive days of exercise. In addition, vascular volumes and selected haematological properties were also examined. The subjects, healthy males between the ages of 19 and 30 years of age, cycled for 2 h per day at approximately 59% of pre-training peak oxygen consumption (VO₂) i.e., maximal oxygen consumption (VO_{2 max}). Following the training,VO_{2 max} (1·min^–1) increased (P<0.05) by 4.3% (3.94, 0.11 vs 4.11, 0.11; mean, SE) whereas maximal exercise ventilation (V _E,max) and maximal heart rate (_c,max) were unchanged. During submaximal exercise,VO₂ was unaltered by the training whereas carbon dioxide production (V _E) and respiratory exchange ratio were all reduced (P<0.05). The altered activity pattern failed to elicit adaptations in either submaximal exercise cardiac output or arteriovenous O₂ difference. _c was reduced (P<0.05). Plasma volume (PV) as measured by¹²⁵I human serum albumin increased by 365 ml or 11.8%, while red cell volume (RCV) as measured by⁵¹chromium-labelled red blood cells (RBC) was unaltered. The increase in PV was accompanied by reductions (P<0.05) in haematocrit, haemoglobin concentration (g. 100 ml^–1), and RBCs (10⁶ mm^–3). Collectively these changes suggest only minimal adaptations in maximal oxygen transport during the early period of prolonged exercise training. However, as evidenced by the changes during submaximal exercise, both the ventilatory and the cardiodynamic response were altered. Since RCV did not change, it is suggested that the elevated PV accompanying training is instrumental in eliciting the change in cardiac function.     

Effect of cold exposure (−15°C) and Salbutamol treatment on physical performance in elite nonasthmatic cross-country skiers

The effects of whole-body exposure to ambient temperatures of −15°C and 23°C on selected performance-related physiological variables were investigated in elite nonasthmatic cross-country skiers. At an ambient temperature of −15°C we also studied the effects of the selective β₂-adrenergic agonist Salbutamol (0.4 mg × 3) which was administered 10 min before the exercise test. Eight male cross-country skiers with known maximal oxygen uptakes (V˙O_{2 max} ) of more than 70 ml · kg⁻¹ · min⁻¹ participated in the study. Oxygen uptake (V˙O₂), heart rate (f _c), blood lactate concentration ([La⁻]_b) and time to exhaustion were measured during controlled submaximal and maximal running on a treadmill in a climatic chamber. Lung function measured as forced expiratory volume in 1 s (FEV₁) was recorded immediately before the warm-up period and at the conclusion of the exercise protocol. Submaximal V˙O₂ and [La⁻]_b at the two highest submaximal exercise intensities were significantly higher at −15°C than at 23°C. Time to exhaustion was significantly shorter in the cold environment. However, no differences in V˙O_{2 max} or f _c were observed. Our results would suggest that exercise stress is higher at submaximal exercise intensities in a cold environment and support the contention that aerobic capacity is not altered by cold exposure. Furthermore, we found that after Salbutamol inhalation FEV₁ was significantly higher than after placebo administration. However, the inhaled β₂-agonist Salbutamol did not influence submaximal and maximal V˙O₂, f _c, [La⁻]_b or time to exhaustion in the elite, nonasthmatic cross-country skiers we studied. Thus, these results did not demonstrate any ergogenic effect of the β₂-agonist used. Accepted: 18 August 1997     

Impact of menstrual cycle phase on the exercise status of young,sedentary women

The purpose of the present study was to compare exercise status during the follicular (FP) and luteal (LP) phases of the menstrual cycle of a single group of young, sedentary women, where the marked differential in the blood concentrations of 17-oestradiol ([E₂]) and progesterone ([P₄]) has the potential to alter the metabolic response to exercise. Fourteen females [21.8 (4.0) years, peak oxygen uptake (V̇O_2peak) <45 ml·kg ^–1·min^–1] performed both incremental exercise to exhaustion and steady-state submaximal cycle ergometer exercise while measurements were made of several metabolic and hormonal variables. With the incremental exercise test, time to exhaustion, maximal power output and total work done were not different between the two phases, nor were the absolute values for V̇O_2peak or the corresponding values for ventilation (V̇E), respiratory frequency (f_R) and heart rate (HR). Resting, end-exercise and peak (post-exercise) plasma lactate concentrations and the lactate threshold were not different between the two phases either. However, as the workloads increased during the incremental protocol, plasma lactate concentration, carbon dioxide output (CO₂) and the respiratory exchange ratio (RER) all were lower during LP, while oxygen uptake (V̇O₂) was higher. With steady-state submaximal exercise, at workloads corresponding to 25% and 75% of menstrual cycle phase-specific O_2peak, V̇O₂ and the oxygen pulse (V̇O₂/HR) were higher and RER and plasma lactate concentration lower during LP. Regardless of phase, [E₂] increased with both incremental and steady-state submaximal exercise, while [P₄] was unchanged. It is concluded that while exercise capacity, as defined by O_2peak and the lactate threshold, is unaffected by cycle phase in young, sedentary women, the metabolic responses in the LP during both incremental and steady-state submaximal exercise suggest a greater dependence on fat as an energy source.     

Cardiovascular and respiratory responses to passive leg cycle exercise in people with spinal cord injuries

The purpose of this study was to determine the effect of passive leg cycle exercise (PLE) on cardiovascular and respiratory responses in people with spinal cord injuries (PSCI). Eight PSCI with lesions from T8 to L1 and five control subjects (CS) performed PLE at pedalling frequencies of 20 or 40 rpm for 7 min at room temperature of about 25°C. We measured, at rest and during PLE, the pulmonary ventilation (V_E), oxygen uptake (VO₂), cardiac output (Q), stroke volume (SV), heart rate (HR) and arterial blood pressure, as well as the skin blood flow (SBF) in the lower limb after PLE. An increase in pedalling frequency promoted an increase in V_E and VO₂ in both groups. Compared with the CS, the PSCI showed significantly smaller increases in VO₂ (P < 0.05). The Q_c was significantly elevated during PLE at 20 and 40 rpm in CS, and at 40 rpm in PSCI (P < 0.05). In CS, it resulted from increases in both SV and HR, whereas in PSCI, it was contributed to by a greater increase in SV without a rise in HR. In CS, the increase in pedalling frequency promoted the increases in SV and HR and consequently in Q_c In PSCI, however, the values remained constant irrespective of pedalling frequency. The arterial blood pressure and SBF in the lower limbs were unchanged by PLE in both groups. These results would suggest that passive leg exercise promotes venous return from the paralyzed lower limbs in PSCI.     

Blood flow velocity in the common carotid artery in humans during graded exercise on a treadmill

Cerebral blood volume flow and flow velocity have been reported to increase during dynamic exercise, but whether the two increase in parallel and whether both increases occur as functions of exercise intensity remain unsettled. In this study, blood flow velocity in the common carotid artery was measured using the Doppler ultrasound method in eight healthy male students during graded treadmill exercise. The exercise consisted of stepwise progressive increases and decreases in exercise intensity. The peak intensity corresponded to approximately 85% of maximal oxygen consumption. During this exercise, the heart rate (f _c), mean blood pressure (BP) in the brachial artery and mean blood flow velocity (_cc) in the common carotid artery increased as functions of exercise intensity. At the peak exercise intensity, (f _c), BP and _cc increased by 134.5%, 20.5% and 51.8% over the control levels before exercise (P < 0.01), respectively. The resistance index (RI) and pulsatility index (PI) were determined from the velocity profile and were expected to reflect the distal cerebral blood flow resistance. The RI and PI increased during the graded exercise, but tended to decrease at the highest levels of exercise intensity. As _cc increased with increases in exercise intensity it would be expected that cerebral blood flow would also increase at these higher intensities. It is also suggested that blood flow velocity in the cerebral artery does not proportionately reflect the cerebral blood flow during dynamic exercise, since the cerebral blood flow resistance changes.     

Aerobic performance capacity in paraplegic subjects

Summary To determine adaptation to prolonged exercise in paraplegics, maximal O₂ uptake ( ) and lactate threshold (LT) were evaluated during an arm cranking exercise in nine patients (P) and nine able-bodied (AB) subjects.Mean averaged 25.1 and 31.6 ml · min^–1 · kg^–1 in P and AB groups respectively. in P was found to be directly related to the level of spinal injury: the higher the lesion the lower the uptake. Lactate threshold expressed as a percentage of was higher in P (59%) than in AB (43%), and close to that observed in armtrained athletes.Since training has less effect on in paraplegics than in able-bodied subjects, attributable to a deficiency in the circulatory adaptation of paraplegics to exercise, the observed differences between AB and P in lactate threshold and submaximal exercise indicate that the possible effect of training in paraplegics is located at the level of intracellular chemistry, with a diminution in glycogenolysis (higher LT) and a higher rate of lipid utilization (lower RQ).     

Validity of heart rate and ratings of perceived exertion as indices of exercise intensity in a group of children while swimming

Summary The purpose of this study was to investigate the validity of heart rate (f _c) and ratings of perceived exertion (RPE) as indices of exercise intensity in a group of children while swimming. Six healthy male swimmers, aged 10–12, swam tethered using the breast-stroke in a flume. The resistance started at 1.0 kg and increased in 1.0 kg steps up to the point of their exhaustion. The subjects swam for 5 min during each period, with a rest of 10–20 min until they had returned to their resting f _c level. The last exercise intensity was with the maximal mass the subjects could support for 2 min. The last min of oxygen consumption (VO₂) and 30 s of f _c were measured during each exercise period. The subjects gave their RPE assessment at the end of exercise.The individual relationships between f _c and VO₂, and percentage maximal oxygen consumption (% VO_2max, were linear with a high correlation r=0.962–0.996 and r=0.962–0.996, respectively. Therefore, it was concluded that f _c was valid as an index of the exercise intensity of children while swimming. Compared to the results found in adults using a similar protocol, the children's f _c were 8.3–26.9 beats·min^–1 higher than those of the adults at the given % VO_2max. The present study showed two different patterns in the relationship between VO₂ and RPE in individuals. In two subjects the RPE increased linearly with VO₂ while in the other four subjects the increase was discontinuous. If f _c and RPE were to be applied to the setting and evaluation of exercise intensity during swimming, it would seem that f _c would be a more useful guide than RPE for some children.     

Ratings of perceived exertion and affect in hot and cool environments

Summary The effects of hot and cool environments on perceptual and physiological responses during steady-state exercise were examined in men (n = 14) performing 30 min of constant exercise (cycle ergometry) at a perceived exertion of somewhat hard. Subjects exercised at the same absolute exercise intensity in hot (40°C), neutral (24°C), and cool (8°C) conditions. Data were collected for differential ratings of perceived exertion (RPE), affect, thermal sensation, mean skin ( ) (and rectal temperatures (T _re), and cardiac frequency (f_c). The subjects completed the hot exposure with an average {ei174-2}_sk of 37.5°C (SEM 0.11), while the neutral and cool conditions produced values of 33.8 (SEM 0.09) and 28.2°C (SEM 0.30), respectively. The was significantly higher in the hot than the neutral and cool conditions throughout exercise (P < 0.05). The f_c was significantly lower in the cool than in the other conditions (P < 0.05), and the subjects completed the hot exposure with a mean f_c more than 20 beats · min^–1 greater than observed in the other conditions. The subjects felt worse (lower affect) in the heat throughout exercise (P < 0.05). Overall RPE was significantly lower in the cool than in the heat, while chest RPE scores for the cool and hot conditions were displaced vertically by approximately two points. Subjects perceived work to be harder, felt worse, and experienced greater thermal sensation in the hot condition, compared with the neutral and cool conditions. Changes in cutaneous vasomotor tone and heat-induced influences on the chest may have accounted for the RPE changes observed in the heat.     

Cardiovascular responses to upright and supine exercise in humans after 6 weeks of head-down tilt (−6°)

Seven healthy men performed steady-state dynamic leg exercise at 50 W in supine and upright postures, before (control) and repeatedly after 42 days of strict head-down tilt (HDT) (−6°) bedrest. Steady-state heart rate (f _c), mean arterial blood pressure, cardiac output (Q˙ _c), and stroke volume (SV) were recorded. The following data changed significantly from control values. The f _c was elevated in both postures at least until 12 days, but not at 32 days after bedrest. Immediately after HDT, SV and Q˙ _c were decreased by 25 (SEM 3)% and 19 (SEM 3)% in supine, and by 33 (SEM 5)% and 20 (SEM 3)% in upright postures, respectively. Within 2 days there was a partial recovery of SV in the upright but not in the supine posture. The SV and Q˙ _c during supine exercise remained significantly decreased for at least a month. Submaximal oxygen uptake did not change after HDT. We concluded that the cardiovascular response to exercise after prolonged bedrest was impaired for so long that it suggested that structural cardiac changes had developed during the HDT period. Accepted: 6 June 2000     

Effect of electrical stimulation of leg muscles on physiological responses during arm-cranking exercise in healthy men

The purpose of this study was to investigate the hypothesis that changes in physiological responses during arm-cranking exercise using electrical stimulation of the leg muscles (ACE-ES) compared to arm-cranking exercise alone (ACE) in able-bodied subjects (ABS) are based on an increase in active muscle mass rather than the enhancing effect of the leg muscle pump. In ABS the sympathetic nervous system induced vasoconstriction and activity of the leg muscle pump are intact, therefore, a normal redistribution of blood takes place during exercise. Consequently, ES should have no additional effect on the redistribution of blood in these ABS during exercise and, thus, changes in physiological responses will be based on an increase in active muscle mass. A group of 11 ABS performed three maximal arm-cranking tests. In the first test peak power output (PO _peak) was determined. The other tests were both submaximal and maximal ACE, once with ACE-ES and once with ACE. The PO _peak was not significantly different between ACE-ES and ACE. Oxygen uptake ( O₂) increased significantly during ACE-ES compared to ACE. Cardiac output ( ), stroke volume (SV), heart rate and ventilation were not significantly different during ACE-ES compared to ACE. Respiratory exchange ratios were significantly lower during ACE-ES compared to ACE at 60% PO _peak and at maximal exercise. In conclusion, ACE-ES caused significant increases in O₂ with a lack of elevation in and SV during submaximal and maximal exercise in ABS. The results of this study suggest that changes in physiological responses during ACE-ES are based on an increase in the active muscle mass rather than stimulation of the leg muscle pump.     

Oxygen uptake during swimming in a hypobaric hypoxic environment

Summary The purpose of this study was to determine oxygen uptake O₂) at various water flow rates and maximal oxygen uptake ( O_2max) 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 ( CO₂), pulmonary ventilation ( _E) and tidal volume (V _T) were significantly greater in H than in N. There were no significant differences in the response of submaximal O₂, heart rate (f _c) or respiratory frequency (f _R) between N and H. Maximal _E,f _R,V _T,f _c blood lactate concentration and water flow rate were not significantly different between N and H. However, VO_2max 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.     

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

Summary Cardiorespiratory responses during armstroke-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 (f _c), pulmonary ventilation ( _E) and respiratory frequency (f _R) during swimming using hands alone (H) were significantly higher than when aided by paddles (P). There were no significant differences in tidal volume (V _T) 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 ( O_2peak,f _c, _E,f _R,V _T and the blood lactate concentration at which O_2peak 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.