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.     

Stroke volume response to progressive exercise in athletes engaged in different types of training

Summary Using the impedance cardiography method, heart rate ( _c) matched changes on indexed stroke volume (SI) and cardiac output (CI) were compared in subjects engaged in different types of training. The subjects consisted of untrained controls (C), volleyball players (VB) who spent about half of their training time (360 min · week^–1) doing anaerobic conditioning exercises and who had a maximal oxygen uptake ( ) 41% higher than the controls, and distance runners (D) who spent all their training time (366 min·week^–1) doing aerobic conditioning exercises and who had a 26% higher than VB. The subjects performed progressive submaximal cycle ergometer exercise (10 W·min^–1) up to _c of 150 beats·min^–1. In group C, SI had increased significantly (P<0.05) at _c of 90 beats·min^–1 ( + 32%) and maintained this difference up to 110 beats·min^–1, only to return to resting values on reaching 130 beats·min^–1 with no further changes. In group VB, SI peaked (+ 54%) at _c of 110 beats·min^–1, reaching a value significantly higher than that of group C, but decreased progressively to 22010 of the resting value on reaching 150 beats·min^–1. In group D, SI peaked at _c of 130 beats·min^–1 (+ 54%), reaching a value significantly higher than that of group VB, and showed no significant reduction with respect to this peak value on reaching 150 beats·min^–1. As a consequence, the mean CI increase per _c unit was progressively higher in VB than in C (+46%) and in D than in VB (+ 105%). It was concluded that thef _c value at which SI ceased to increase during incremental exercise was closely related to the endurance component in the training programme.     

The physical demands of riding in National Hunt races

Heart rate (f _c) and post-competition blood lactate concentration ([La⁺]) were studied in seven male professional National Hunt jockeys over 30 races. Thef _c response for individual races followed a similar pattern for all subjects. The mean peakf _c recorded during competition was 184 beats·min^–1 (range 162–198 beats·min^–1) with averagef _c during the races ranging from 136 to 188 beats·min^–1. During consecutive races the recoveryf _c did not return to resting values. The mean [La⁺] was 7.1 mmol·l^–1 (range 3.5–15.0 mmol·l^–1). The conclusions of this study suggest that riding in National Hunt races is a physically demanding occupation. The muscular activity in this profession requires a high metabolic drive and produces a significant cardiorespiratory response.     

Responses of subjects with spinal cord injuries to maximal wheelchair exercise: comparison of discontinuous and continuous protocols

Summary Six male subjects with spinal cord injuries (SCI) participated in this investigation to compare peak values of oxygen uptake ( O₂). heart rate (f _c), ventilation ( _E), respiratory exchange ratio (R) and power output (W) obtained using a discontinuous (DP) and a continuous jump max protocol (JMP) in a maximal wheelchair exercise test on a treadmill. The W increments were achieved by imposing an extra mass upon the wheelchair through a pulley system. The DP involved exercise periods of 3 min separated by 2-min intervals at relative rest. Increments in W consisted of 0.10 or 0.15 W · kg^–1 total mass. During the rest intervals no mass was imposed on the wheelchair. The JMP involved an increase in W each minute. Increments and velocity in the JMP were the same as during the exercise periods for DP. Mean peak values for W [99.5 (SD 13.6) W], O₂ [2.13 (SD 0.27) l · min^–1, standard temperature and pressure, dry], R [1.25 (SD 0.16)] and _E [82.8 (SD 11.2) l · min^–1, body temperature and pressure, saturated] in DP were not different from values observed for W [103.5 (SD 13.1)], O₂ [2.18 (SD 0.31) l · min^–1], R [1.17 (SD 0.16)] and _E [78.9 (SD 16.0) l · min^–1] in the JMP. The only significant difference was observed for f _c: 198 (SD 11) beats · min^–1 in DP and 187 (SD 11) beats · min^–1 in JMP. The higher values for f _c elicited using DP have been discussed. It was concluded that both a DP and a JMP seem to be equally appropriate in determining peak O₂ and peak W in SCI persons. In terms of time saving, JMP would seem to be a more favourable protocol.     

Effect of pyridostigmine on the exercise-heat response of man

Summary The effect of pyridostigmine on thermoregulatory responses was evaluated during exercise and heat stress. Eight heat acclimated, young adult male subjects received four doses of pyridostigmine (30 mg) or identical placebo tablets every 8 h, in a double blind, randomized, cross-over trial. A 30.3%, SD 4.6% inhibition of the circulating cholinesterase (ChE) activity was induced in the pyridostigmine-treated group. The subjects were exposed to 170-min exercise and heat-stress (dry bulb temperature, 33° C; relative humidity 60%) consisting of 60 min in a sitting position and two bouts of 50-min walking (1.39 m · s^–1, 5% gradient) which were separated by 10-min rest periods. No differences were found between treatments in the physiological responses and heat balance parameters at the end of exposure: heart rate (f _c) was 141 beats · min^–1, SD 16 and 150 beats · min^–1, SD 12, rectal temperature (T _re) was 38.5°C, SD 0.4° and 38.6°C, SD 0.3°, heat storage was 60 W · m^–2, SD 16 and 59 W · m^–2, SD 15 and sweat rate was 678 g · h^–1, SD 184 and 661 g · h^–1, SD 133, in the pyridostigmine and placebo treatments, respectively. The changes in T _re and f _c over the heat-exercise period were parallel in both study and control groups. Pyridostigmine caused a slight slowing of f _c (5 beats·min^–1) which was consistent throughout the entire exposure (P<0.001) but was of no clinical significance. The overall change in f_c was similar for both groups. We have concluded that pyridostigmine administration, in a dose sufficient to induce a moderate degree of ChE inhibition, does not significantly affect performance of exercise in the heat.     

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.     

Verification of the heart rate threshold

Among the methods for determining anaerobic threshold (AT), the heart rate (HR) method seems to be the simplest. On the other hand, many conflicting results from comparing this method with others have been presented over the last 10 years. Therefore, the aim of this study was to compare the heart rate threshold (HRT) with the lactate turn point (LTP) —second break point of dependence of lactate (LA) to power output, ventilatory threshold (VT) and threshold determined by electromyography (EMG_AT), all determined by the same exercise test and evaluated by the same computer algorithm. A group of 24 female students [mean age 20.5 (SD 1.6) years, maximal oxygen consumption 48.8 (SD 4.7) ml · kg^–1 · min^–1 performed an incremental exercise test on a cycle ergometer (modified Conconi test) starting with an initial power output (PO) of 40 W with intensity increments of 10 W · min^–1 until the subjects were exhausted. The HRT, LTP and EMG_AT determination was done by computer-aided break-point regression analysis from dependence of functional measures on PO. The same computer algorithm was used for VT determination from the relationship between ventilation (V) and oxygen uptake ( O₂) or carbon dioxide output ( CO₂). Nonsignificant differences were found between HRT [ O₂ 35.2 (SD 4.2) ml · kg^–1 · min^–1; HR 170.8 (SD 5.5) beats min^–1; LA 4.01 (SD 1.03) mmol · l^–1; PO 2.27 (SD 0.33) W · kg^–1 VT [ O₂ 35.1 (SD 3.7) ml · kg^–1 · min^–1 HR 168.3 (SD 4.8) beats · min^–1; LA 3.87 (SD 1:17) mmol · l^–1; PO 2.22 (SD 0.27) W · kg^–1 EMG_AT [ O₂35.6 (SD 4.1) ml · kg^–1 · min^–1 HR 171.0 (SD 5.4) beats · min^–1; LA 4.11 (SD 0.98) mmol · l^–1; PO 2.30 (SD 0.31) W · kg^–1] and LTP [ O₂) 35.3 (SD 4.1) ml · kg^–1 · min^–1; HR 170.1 (SD 6.0) beats · min^–1; LA 3.99 (SD 0.76) mmol · l^–1; PO 2.27 (SD 0.29) W · kg^–1]. Highly significant correlations (P < 0.01 in all cases) were found among all measurements made at threshold level in all the thresholds investigated. Correlation coefficients ranged in selected variables at different threshold levels from 0.842 to 0.872 in O₂ measured in ml · kg^–1 · min^–1, from 0.784 to 0.912 for LA, from 0.648 to 0.857 for HR, and from 0.895 to 0.936 for PO measured in W · kg^–1. These findings have led us to conclude that HRT could be used as an alternative method of determining anaerobic threshold in untrained subjects.     

Heart rate threshold related to lactate turn point and steady-state exercise on a cycle ergometer

The aim of this study was to investigate heart rate threshold (HRT) related exercise intensities by means of two endurance cycle ergometer tests using blood lactate concentration. [La], pulmonary ventilation ( _E), oxygen uptake ( ), heart rate (HR) and electromyogram (EMG) activity of working muscle. Firstly, 16 healthy female students [age, 21.4 (SD 2.8) years; height, 167.1 (SD 5.1) cm; body mass 62.7 (SD 7.1) kg] performed an incremental exercise test (10 W each minute) on an electrically braked cycle ergometer until they felt exhausted. The HRT and lactate turn point (LTP) were assessed by means of computer-aided linear regression break point analysis from the relationship of HR or [La] to power output. No significant difference was found between HRT and LTP for all the variables measured. Secondly, two endurance tests (ET) of 20 min duration were performed by 7 subjects. The first (ET I) was performed at an exercise intensity which was about 10% lower than the power output at HRT [61.2 (SD 3.1) % maximal oxygen uptake ( _max)], the second (ET II) at an exercise intensity about 10% higher than the power output at HRT [79.2 (SD 3.4) % _max]. The parameters measured showed a clear steady state in ET I. All mean values were lower than values at HRT [power, 138.7 (SD 18.9) W; HR, 172.1 (SD 4.7) beats·min^–1; , 2.2 (SD 0.3) l·min^–1; _E, 54.0 (SD 9.1) l·min^–1; [La], 3.7 (SD 1.1) mmol·l^–1; EMG, 81.1 (SD 24.0) V] except HR which was the same. No parameters showed a steady state (except EMG activity) in ET II. No subject was able to maintain the exercise for the whole 20 min in ET II [mean time to cessation of the exercise was 10.4 (SD 3.7) min]. At the end of ET II all variables measured were significantly higher (P < 0.05) than in ET I (except EMG activity) [HR, 184.3 (SD 5.2) and 172.1 (SD 8.7) beats·min^–1; _E: 75.2 (SD 11.7) and 49.6 (SD 8.4) l·min^–1; , 2.9 (SD 0.7) and 2.1 (SD 0.5) l·min^–1; [La], 7.0 (SD 1.8) and 3.3 (SD 2.2) mmol·l^–1; EMG, 86.3 (SD 28.7) and 75.9 (SD 21.5) V]. Although no exercise, at HRT exactly was performed, we assume that maximal steady state lay in between ET I and ET II.     

Heart rate overshoot at the beginning of muscle exercise

Summary A characteristic notch in the heart rate (f _c) on-response at the beginning of square-wave exercise is described in 7 very fit marathon runners and 12 sedentary young men, during cycle tests at 30% and 60% of maximal oxygen consumption (VO_2max). The (f _c) notch revealed af _c overshoot with respect to the (f _c) values predicted from exponential beat-by-beat fitted models. While at 30% of (VO_2max). all subjects showed af _c over-shoot, at 60% of (VO_2max). it occurred in the marathon runners but not in the sedentary subjects. The mean time of occurrence of thef _c overshoot from the onset of the exercise was 16.7 (SD 4.7) s and 12.2 (SD 3.2) s at 30% of (VO_2max). in the runners and the sedentary subjects respectively, and 23.8 (SD 8.8) s at 60% of (VO_2max). in the runners. The amplitude of the overshoot, with respect to rest, was 41 (SD 12) beats·min^–1and 31 (SD 4) beats·min^–1 at 30% of (VO_2max). in the runners and the sedentary subjects respectively, and 46 (SD 19) beats·min^–1 at 60% of (VO_2max). in the runners. The existence and the amplitude of thef _c overshoot may have been related to central command and muscle heart reflex mechanisms and thus may have been indicators of changes in the balance between sympathetic and parasympathetic activity occurring in fit and unfit subjects.     

Cardiovascular responses to facial cooling during low and moderate intensity exercise

Summary To investigate the hypothesis that facial cooling (FC) exerts a greater influence on the cardiovascular system at lower versus higher levels of exercise, this study examined the effect of facial cooling [mean (SE): 0 (2)°C at 0.8 m·s^–1 wind velocity] during 30 min low [35% maximum oxygen consumption ( O_2max)] and moderate (70% O_2max) levels of cycle ergometry in the supine position. Five male subjects were assigned in random order to four exercise conditions: (1) FC at 35% O_2max(FC35), (2) no cooling (NFC35), (3) FC at 70% O_2max(FC70), and (4) no cooling (NFC70). Heart rate (f _c), stroke volume (V _s), and cardiac output ( _c) were measured at rest and every 10 min of exercise using impedance cardiography. During FC35, the change in f _c [mean (SE)] was significantly lower (P < 0.05) than NFC35 at 10 [22 (5) vs 31 (3) beats· min^–1], 20 [29 (6) vs 35 (3) beats·min^–1], and 30 [29 (5) vs 38 (4) beats·min^–1] min. No differences in f _c were observed between FC70 and NFC70. Furthermore, FC had no effect on V _s or _cat either exercise intensity. However, when comparing the FC70 and NFC70 conditions, there was a significant main effect (P<0.05) in mean arterial pressure (P _a) response with cooling despite the fact that neither V _s or _cwere different from the NFC70 control. The increase (P < 0.05) in the estimated change in systemic vascular resistance ( _a· _c ^–1) could partly explain the relative rise in _aat FC70. No pressor effect of cooling was observed at 35% O_2max. The results suggest that the FC condition promotes exercise bradycardia at low levels of exercise and exerts a greater pressor response during moderate exercise.     

Effect of work rate increment on peak oxygen uptake during wheelchair ergometry in men with quadriplegia

Summary The purpose of this study was to determine the effect of work rate increment on peak oxygen uptake ( peak) during wheelchair ergometry (WCE) in men with quadriplegia due to cervical spinal cord injuries (CSCI). Twenty-two non-ambulatory subjects (aged 20–38 years) with CSCI were divided into two groups based on wheelchair sports classification (n = 12 for IA group and n = 10 for IB/IC group). Subjects underwent three different, continuous graded exercise tests (spaced at least 1 week apart) on an electronically braked wheelchair ergometer. Following a 3-min warm-up, the work rate was increased 2, 4, or 6 W · min^–1 for the IA group and 4, 6, or 8 W · min^–1 for the IB/IC group. Ventilation and gas exchange were measured breath-by-breath with a computerized system. Repeated-measures ANOVA showed no significant difference among the three protocols for peak in the IA group (P>0.05). The mean (SD) peak values (ml · kg^–1 · min^–1) were 9.3 (2.4), 9.4 (3.2), and 8.4 (2.6) for the 2, 4, and 6 W · min^–1 protocols, respectively. In contrast, the IB/IC group showed a significant difference among the protocols for peak (P<0.05). The mean (SD) peak values (ml · kg^–1 · min^–1) were 15.1 (4.0), 14.1 (4.4), and 12.7 (4.0) for the 4, 6, and 8 W · min^–1 protocols, respectively. Post hoc analysis revealed a difference between the 4 and 8 W · min^–1 protocols. Our results suggest that graded exercise testing of men with quadriplegia due to CSCI, using WCE, should employ work rate increments between 2 and 6 W · min^–1 and that work rate increments of 8 W · min^–1 or greater will result in an underestimate of peak.     

A study of lactate metabolism without tracer during passive and active postexercise recovery in humans

Tracers have been used extensively to study lactate metabolism in humans during rest and exercise. Nevertheless, quantification of in vivo lactate kinetics as measured by lactate tracers remains controversial and new data are necessary to clarify the issue. The present study has developed a simple kinetic model which does not require labelled molecules and which yields proportional and quantitative information on lactate metabolism in humans during postexercise recovery performed at different levels of intensity. Five subjects took part in six experiments each of which began with the same strenuous exercise (StrEx; 1 min, 385 W, 110 rpm). The StrEx of each session was followed by a different intensity of recovery: passive recovery (PR) and active recoveries (AR) with power outputs of 60, 90, 120, 150 and 180 W, respectively. Blood lactate concentration was measured prior to and immediately after StrEX and regularly during the 1st h of recovery. Oxygen uptake ( ) was measured every 30 s during the whole session. The results showed that the disappearance rate constant (k_e) increases abruptly from PR [0.080 (SEM 0.004) min^–1] to moderate AR [60W: 0.189 (SEM 0.039) min^–1] and decreases slowly during more intense AR [180 W: 0.125 (SEM 0.027) min^–1]. The lactate apparent clearance (Cl·F^–1) was calculated from the area under the lactate concentration-time curve. The Cls·F^–1 increased 1.81 (SEM 0.17) fold from PR to moderate AR (60 W) and only 1.31 (SEM 0.14) from PR to the most intense AR (180 W). Using the model, the apparent lactate production (FK₀) was also calculated. The FK₀ increased regularly following a slightly curvilinear function of and was 2.61 (SEM 0.53) fold greater during the most intense AR (180 W) than during PR. Because of the lack of data concerning the size of apparent lactate distribution volume (V _d), the apparent turnover rate (R_bl) has been presented here related toV _d. The R_bl·V _d ^–1 increased also following a slightly curvilinear function of . The R_bl·V _d ^–1 was 85.90 (SEM 14.42) mol·min^–1·l^–1 during PR and reached 314.09 (SEM 153.95) mol·min^–1·l^–1 during the most intense AR (180 W). In conclusion the model presented here does not require labelled molecules and firstly makes it possible to follow the proportional change of apparent lactate clearance and apparent lactate production during active postexercise recovery in comparison with passive recovery conditions and secondly to estimate the blood lactate turnover.     

Comparison of mathematically determined blood lactate and heart rate “threshold” points and relationship with performance

Summary The purpose of this study was to investigate the relationship between threshold points for heart rate ( ) and blood lactate (Th_1a) as determined by two objective mathematical models. The models used were the mono-segmental exponential (EXP) model of Hughson et al. and the log-log (LOG) model of Beaver et al. Inter-correlations of these threshold points and correlations with performance were also studied. Seventeen elite runners (mean, SD = 27.5, 6.5 years; 1.73, 0.05 m; 63.8, 7.3 kg; and maximum oxygen consumption of 67.8, 3.7 ml · kg^–1 · min^–1) performed two maximal multistage running field tests on a 183.9-m indoor track with inclined turns. The initial speed of 9 km · h^–1 (2.5 m · s^–1) was increased by 0.5 km · h^–1 (0.14 m · s^–1) every lap for thef _c test and by 1 km · h^–1 (0.28 m · s^–1) every 4 min for the la test. After fitting the la or thef _c data to the two mathematical models, the threshold speed was assessed in the LOG model from the intersection of the two linear segments (LOG-1a; LOG-f _c) and in the EXP model from a tangent point (TI-1a; TI-f _c). Th_1a and speeds computed with the two models were significantly different (P<0.001) and poorly correlated (LOG-1a vs LOG-f _c:r=0.36, TI-1a vs TI-f _c:r=0.13). In general, were less well correlated with performance than Th_1a. With two different objective mathematical models, this study has shown significant differences and poor correlations between Th_1a and . Thus thef _c inflection point with Conconi's protocol is a poor indicator of the la breakpoint with a conventional multistage protocol and a weaker indicator of running performance.     

The oxygen uptake-power regression in cyclists and untrained men: implications for the accumulated oxygen deficit

The regression of oxygen uptake (O₂) on power output and the O₂ demand predicted for suprapeak oxygen uptake (O_2peak) exercise (power output = 432 W) were compared in ten male cyclists [C, mean O_2peak = 67.9 (SD 4.2) ml · kg^–1 · min^–1] and nine active, yet untrained men [UT, mean O_2peak = 54.1 (SD 6.5) ml · kg^–1 · min^–1]. The O₂-power regression was determined using a continuous incremental cycle test (CON4), performed twice, which comprised several 4-min exercise periods progressing in intensity from approximately 40%–85% O_2peak. Minute ventilation (_E), heart rate (HR), respiratory exchange ratio (R), blood lactate concentration ([1a^–]_b) and rectal temperature (T _re) were measured at rest and during CON4. The slope of the O₂-power regression was greater (P 0.05) in C [12.4 (SD 0.7) ml · min^–1. W^–1] compared to UT [11.7 (SD 0.4) ml · min^–1 W^–1]; as a result, the O₂ demand (at 432 W) was also higher (P 0.05) in C [5.97 (SD 0.23) l · min^–1] than UT [5.70 (SD 0.15) 1 · min^–1]. ExerciseR and [la^–]_b were lower (P 0.05) in C .in comparison to UT at all power outputs, whereas _E and HR were relatively lower (P 0.05) in C at power outputs approximating 180 W, 220 W and 270 W. Differences in fat metabolism estimated over the first three power outputs accounted for approximately 19% of the difference in O₂-power slopes between the groups and up to 46% of the difference in O₂ at a given intensity. Although the O₂-power regressions were linear for C [r = 0.997 (SD 0.001)] and UT [r = 0.997 (SD 0.001)], the O₂-power slope was higher at power outputs at or above the lactate threshold (13.2 ml · min^–1 · W^–1 than at lower intensities (11.6 ml · min^–1 · W^–1) in C, an effect which was less profound in UT. As a result, the exclusion of O₂ at the highest power outputs completely abolished the difference in O₂-power slopes between C and UT. Thus, the relatively higher O₂ during incremental exercise in C can be almost entirely attributed to the higher O₂ cost of cycling at higher power outputs. In addition, the presence of non-linear responses in O₂ at higher intensities also confirms the invalidity of describing the O₂ response across a wide range of power outputs using a linear function, and challenges the validity of predicting the O₂ demand of more intense exercise by a linear extrapolation of this same function.     

Maximal heart rates and plasma lactate concentrations observed in middle-aged men and women during a maximal cycle ergometer test

Summary The purpose of this study was to investigate criteria for maximal effort in middle-aged men and women undertaking a maximal exercise test until they were exhausted if no measurements of oxygen uptake are made. A large group of 2164 men and 975 women, all active in sports and aged between 40 and 65 years, volunteered for a medical examination including a progressive exercise test to exhaustion on a cycle ergometer. In the 3rd min of recovery a venous blood sample was taken to determine the plasma lactate concentration ([la^–]_{p, 3min}). Lactate concentration and maximal heart rate (f _{c, max}) were lower in the women than in the men (P<0.001). Multiple regression analyses were performed to assess the contribution of sex to [la^–]_{p, 3 min}, independent of age and f _c max, It was found that [la^–]_{p,3 min} was about 2.5 mmol·l^–1 lower in women than in men of the same age and f _{c, max}. In our population 88% of the men and 85% of the women met a combination of the following f _{c, max} and [la^–]_{p, 3min} criteria: f _{c, max} equal to or greater than 220 minus age beats·min^–1 and/or [la^–]_{p, 3min} equal to or greater than 8 mmol·l^–1 in the men and f _{c, max} equal to or greater than 220 minus age beats·min^–1 and/or [la^–]_{p, 3min} equal to or greater than 5.5 mmol·1^–1 in the women.     

Effect of short-term energy intake level and exercise on oxygen consumption in men

Summary The influence of short-term energy intake and cycle exercise on oxygen consumption in response to a 1.5 MJ test meal was investigated in ten young, adult men. On the morning after a previous day's low-energy intake (LE regimen) of 4.5 MJ, the mean resting oxygen consumption increased by 0.7 ml · kg^–1 · min^–1 after the test meal (P<0.025). After a high-energy intake (HE regimen) of 18.1 MJ, the resting measurement was unchanged (+0.4 ml · kg^–1 · min^–1) after the meal (n.s.). These trends are the reverse of what would be expected if oxygen consumption in response to feeding is a factor in the acute control of body weight. The mean fasting oxygen consumption during cycle exercise at 56% of (constant work) for both LE and HE prior intakes was not different at 31.1 ml · kg^–1 · min^–1. Oxygen consumption during exercise increased after feeding by 0.5 ml · kg^–1 · min^–1 on the LE regimen (n.s.) and decreased by 1.2 ml · kg^–1 · min^–1 on the HE regimen (n.s.). These results are also the reverse of what would be expected if oxygen consumption in response to exercise is related to short-term energy intake.     

Cardiorespiratory adaptation with short term training in older men

Summary The purpose of this study was to assess the rate of training-induced cardiorespiratory adaptations in older men [mean (SD), 66.5 (1.2) years]. The eight subjects trained an average of 4.3 (0.3) times each week. The walk/jog training was in two phases with 4 weeks (phase 1) at a speed to elicit 70% of pre-training maximal oxygen consumption ( ), and 5 weeks (phase 2) at 80%. Maximal exercise treadmill tests and a standardized submaximal protocol were performed prior to training, at weekly intervals during the training programme, and after training. (ml·kg^–1·min^–1) increased significantly over both phases: 6.6% after the first 4 weeks, and an additional 5.2% after the final 5 weeks. The weekly changes in over phase 1 were well fitted by an exponential association curve (r=0.75). The half-time for the rate of adaptation was 13.8 days, or 8.3 training sessions. Over phase 2, the change in did not plateau and a time course could not be determined. Submaximal exercise heart rate (f _c ) was reduced a significant 10 beats · min^–1 after the first 4 weeks, and a further 6 beats · min^–1 over the final 5 weeks. Thef _c reductions showed half-times of 9.1 days (phase 1) and 9.8 days (phase 2) (or 5-6 training sessions). The anaerobic ventilation threshold was increased 13.9% over the 9 weeks of training and the respiratory exchange ratio during constant load heavy exercise was significantly reduced; however, these changes could not be described by an exponential time course. Thus, short-term exercise training of older men resulted in significant and rapid cardiorespiratory improvements.     

Changes in acid-base status of marathon runners during an incremental field test

Summary Four top-class runners who regularly performed marathon and long-distance races participated in this study. They performed a graded field test on an artificial running track within a few weeks of a competitive marathon. The test consisted of five separate bouts of running. Each period lasted 6 min with an intervening 2-min rest bout during which arterialized capillary blood samples were taken. Blood was analysed for pH, partial pressure of oxygen and carbon dioxide (P0₂ and PCO₂) and lactate concentration ([la^–]_b). The values of base excess (BE) and bicarbonate concentration ([HCO₃ ^–]) were calculated. The exercise intensity during the test was regulated by the runners themselves. The subjects were asked to perform the first bout of running at a constant heart rate f _c which was 50 beats · min^–1 below their own maximal f _c. Every subsequent bout, each of which lasted 6 min, was performed with an increment of 10 beats · min^–1 as the target f _c. Thus the last, the fifth run, was planned to be performed with fc amounting to 10 beats · min^–1 less than their maximal f _c. The results from these runners showed that the blood pH changed very little in the bouts performed at a running speed below 100% of mean marathon velocity ( _m). However, once _mwas exceeded, there were marked changes in acid-base status. In the bouts performed at a velocity above the _mthere was a marked increase in [la^–]_b and a significant decrease in pH, [HCO₃ ^–], BE and PCO₂. The average marathon velocity ( _m) was 18.46 (SD 0.32) km·h^–1. The [la^–]_b at a mean running velocity of 97.1 (SD 0.8) % of _mwas 2.33 (SD 1.33) mmol ·l^–1 which, compared with a value at rest of 1.50 (SD 0.60) mmol·l^–1, was not significantly higher. However, when running velocity exceeded the vm by only 3.6 (SD 1.9) %, the [la^–]b increased to 6.94 (SD 2.48) mmol·l-1 (P<0.05 vs rest). We concluded from our study that the highest running velocity at which the blood pH still remained constant in relation to the value at rest and the speed of the run at which [la^–]_b began to increase significantly above the value at rest is a sensitive indicator of capacity for marathon running.     

Cardiac stress in glass bangle workers

Summary The cardiac cost of work and recovery pulse rates were evaluated in 38 glass bangle workers (mean age 27.8 years, SD 3.4) exposed to radiant heat (46.2°C, SD 5.1) and high ambient temperature (38.2°C, SD 3.4) for a mean period of 11.0 years, SD 3.5 in the glass bangle industry. A reference group of 15 controls (mean age 27.0 years, SD 3.5 unexposed to occupational heat stress served as a comparison. The results showed that the pulse rate increased from a mean basal value of 80.0 beats·min^–1, SD 2.7 to 113.2 beats · min^–1, SD 11.4 in the exposed workers while in the controls the increase was negligible. Thus the cardiac cost of work was found to be 33.2 beats · min-', SD 11.1 in the exposed group which was significantly higher (P < 0.001) than 7.8 beats·min^–1, SD 4.2 observed in the control group. Among the exposed workers, belanias, who were engaged in the strenuous job of manually rotating the iron roller in the Belan furnace so that the molten glass could be wound in a spiral form, showed the maximum increase in the pulse rate (42.0 beats·min^–1, SD 7.5) over the work-shift followed by muthias (31.1 beats · min^–1, SD 4.0) who were engaged in removing the glass spirals from the Belan furnace. However, wiremen (tarkashs), who were engaged in the highly skilled job of making very fine threads of molten glass with the help of an iron roller, showed the smallest increase (19.5 beats · min^–1, SD 3.4) in pulse rate over the work-shift. To assess the effect of heat stress on the cardiovascular system in the glass bangle workers, the pulse rates were counted in a sitting posture from 30 s to 1 min (R₁), from 2.5 to 3 min (R₃) and from 4.5 to 5 min (R₅) after the completion of their work. The recovery pulse rates at R₁, R₃ and R₅ intervals remained significantly higher than the pre-work value in the exposed group and was most pronounced in belanias. The tarkashs, in contrast, exhibited almost a complete recovery at R₅. The increased cardiac cost of work and the incomplete recovery in pulse rates indicated that these workers exposed to high ambient temperature and thermal radiation in the glass bangle industry suffered from cardiac stress. These findings suggest that the work practices in the glass bangle industry need revising to include a proper work-rest schedule to avoid circulatory strain in the excessive heat to which glass bangle workers are exposed, together with the implementation of suitable engineering controls in order to reduce the level of environmental heat and thermal radiation prevailing in the work environment of the glass bangle industry.     

The effects of cigarette smoking on maximal oxygen consumption and selected physiological responses of elite team sportsmen

Summary The acute and chronic effects of cigarette smoking on selected physiological responses were determined in seven well-trained non-smokers and seven well-trained habitual smokers. Non-smokers and smokers did not differ significantly with respect to maximal oxygen consumption ( ). The acute effect of smoking two cigarettes immediately prior to a graded exercise stress test on a treadmill ergometer did not significantly alter the of either group. However, the time taken for non-smokers to reach exhaustion decreased significantly (F=5.381, P<0.05) by a mean of 0.64 min. Smokers recorded lower scores for forced vital capacity (FVC) and forced expiratory volume in the 1st s exhalation (FEV₁) than non-smokers. Only the mean FVC of smokers recorded 5 min post-exercise was significantly altered by pre-exercise smoking. No differences were found between the resting heart rates (HR) of non-smokers and smokers. Smoking two cigarettes significantly (F=44.720, P<0.01) increased the mean resting HR of smokers and non-smokers by 15.8 beats·min^–1 and 15.6 beats·min^–1 respectively. No alteration to the exercise HR of either group was found under smoking conditions of the tests.