Effect of age on cardiac index,stroke index and left ventricular ejection fraction at rest and during exercise as studied by radiocardiography

Radiocardiography was used to measure cardiac output, stroke volume and left ventricular ejection fraction at rest and during muscular exercise in relation with age in 148 healthy subjects (age range: 6–78 years). A clear dependence of these parameters on age was found. The mean annual decrease at rest was 22±9 ml/min/m² for cardiac index, 0.22±0.04 ml/m² for stroke index and 0.0017±0.0003 for left ventricular ejection fraction. Male subjects had significantly (p < 0.001) greater cardiac (9±4%) and stroke indices (11±23%) than females. During submaximal exercise cardiac index increased from 3.5±0.7 l/min/m' to 8.1±1.6 l/min/m² in male subjects (mean age: 32 years) and from 3.1±0.4 l/min/m² to 7.2±1.2 l/min/ m² in female subjects (mean age: 29 years). The corresponding increases in stroke index and left ventricular ejection fraction were: from 52±7 ml/m² to 62±9 ml/m². from 46±7 ml/m² to 51±9 ml/m² and from 0.66±0.08 to 0.79±0.05 and from 0.64±0.10 to 0.72±0.10. In subjects who were 60 years and older the increases of these parameters during exercise were considerably smaller.     

Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

Summary The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

Time course for strength and muscle thickness changes following upper and lower body resistance training in men and women

 The purpose of this study was to investigate the time course of skeletal muscle adaptations resulting from high-intensity, upper and lower body dynamic resistance training (WT). A group of 17 men and 20 women were recruited for WT, and 6 men and 7 women served as a control group. The WT group performed six dynamic resistance exercises to fatigue using 8–12 repetition maximum (RM). The subjects trained 3 days a week for 12 weeks. One-RM knee extension (KE) and chest press (CP) exercises were measured at baseline and at weeks 2, 4, 6, 8, and 12 for the WT group. Muscle thickness (MTH) was measured by ultrasound at eight anatomical sites. One-RM CP and KE strength had increased significantly at week 4 for the female WT group. For the men in the WT group, 1 RM had increased significantly at week 2 for KE and at week 6 for CP. The mean relative increases in KE and CP strength were 19% and 19% for the men and 19% and 27% for the women, respectively, after 12 weeks of WT. Resistance training elicited a significant increase in MTH of the chest and triceps muscles at week 6 in both sexes. There were non-significant trends for increases in quadriceps MTH for the WT groups. The relative increases in upper and lower body MTH were 12%–21% and 7%–9% in the men and 10%–31% and 7%–8% in the women respectively, after 12 weeks of WT. These results would suggest that increases in MTH in the upper body are greater and occur earlier compared to the lower extremity, during the first 12 weeks of a total body WT programme. The time-course and proportions of the increase in strength and MTH were similar for both the men and the women. Accepted: 6 September 1999     

Relationship between core temperature and skin blood flux in lower limbs during prolonged arm exercise in persons with spinal cord injury

The purposes of the present study were to examine the response of the skin blood flux (SBF) in the paralyzed lower limbs of persons with spinal cord injury (PSCI) and to clarify the relationship between the SBF and core temperature during prolonged arm exercise. Eight male PSCI with lesions from T6 to L5 and six male control subjects (CS) participated in this study. The subjects rested for 60 min and then performed arm-cranking exercise at 20 W for 30 min at 25 °C. The tympanic membrane temperature (T _ty) and SBF in the anterior thigh (SBFT) and in the posterior calf (SBFC) were continuously measured throughout the experiment. The SBFC did not change in either PSCI or CS during the experiment. The SBFT in four PSCI with high lesions (T6 to T12), remained unchanged during exercise. The SBFT in the other four PSCI with low lesions (T12 to L5, SBFT+) began to elevate markedly when the T t, exceeded a threshold temperature of 36.69 °C. The pattern of increase of SBFT in SBFT+ was similar to that in CS, although onset of the increase in SBFT was delayed and the peak of SBFT during exercise was significantly lower in comparison with the CS. We consider that these differences between the SBFT+ and CS were largely attributable to the lowerT _ty in the former group, which took a prolonged time to reach the threshold of 36.69 °C.     

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.     

The effect of caffeine ingestion on physical performance after prolonged exercise

Summary The purpose of this study was to determine the effect of caffeine ingestion on physical performance after prolonged endurance exercise. Twenty three trained male volunteers participated in a 40-km march and were divided into two groups, matched for caffeine clearance rate and aerobic capacity. The experimental group ingested, prior to the march, a caffeinated drink at a dose of 5 mg·kg⁻¹ body mass and at the 3rd and 5th h of marching an additional drink at a dose of 2.5 mg·kg⁻¹ body mass. The control group ingested a drink of equal volume at the same times. Upon termination of the march each subject performed a cycle ergometer test at an intensity of 90% maximal oxygen consumption. Time to exhaustion and rate of perceived exertion (RPE) were recorded. Blood samples were drawn predrink, at the 3rd and 5th h of marching and immediately after the cycle ergometer test, and were analysed for caffeine, free fatty acids (FFA), lactate and glucose levels. Plasma FFA levels increased during the march (p<0.05), with no significant difference between groups. Lactate levels increased in the experimental group (p<0.05), with no significant change in the control group. Glucose levels did not change significantly in either group. After the cycle ergometer test, lactate levels were significantly higher in the experimental, as compared to the control group (3.77±0.33 vs 2.52±0.35 mmol·l⁻¹, respectively). There was no significant difference between treatments in the time to exhaustion on the cycle ergometer, but RPE was different (p<0.05). Under the conditions of this study, the results do not indicate caffeine ingestion as an ergogenic aid which will postpone exhaustion following prolonged endurance exercise. This work was presented, in part, at the Canadian Association of Sports Sciences Annual Meeting, October 1987, Lake Louise, Alberta, Canada     

Serum creatine kinase activity following forearm flexion isometric exercise

Summary The purpose of this study was to 1) compare serum creatine kinase (CK) activity following two forearm flexion isometric exercise regimens differing in work to rest ratio, and 2) examine the CK response to a repeated bout of isometric exercise. Eleven males were tested on two sessions (bouts) spaced 1 week apart. For bout 1, five subjects (group A) performed a forearm flexion isometric exercise consisting of 40 10-s maximal contractions with 20-s inter-trial rests (1020), while six (group B) performed 40 maximal 10-s contractions with 5-s inter-trial rests (105). The increase in serum CK activity following the 1020 exercise (143%) was significantly greater than that following the 105 exercise (52%). The 1020 exercise was also associated with greater tension generation over trials. One week later, both groups performed a bout of 1020 exercise. A substantial reduction in the serum CK response was found following this second bout. The data suggest that for bout 1 the isometric exercise associated with the greater overall tension levels resulted in the greater CK response. However, when the 1020 exercise was repeated 1 week later, a substantial reduction in the CK response was found which was unrelated to the tension generated.This study was supported by a University Faculty Research Grant No. 2-03021     

Hormonal responses to high- and moderate-intensity strength exercise

The hormonal responses of nine male, strength athletes to strength exercise were examined. The athletes performed one moderate- and one high-intensity strength exercise workout. In the high-intensity workout, the load was 100% of each subject's three-repetition maximum (3-RM) for squats and front squats, and 100% of each subject's six-repetition maximum (6-RM) for leg extensions. In the moderate-intensity workout, the load was 70% of the high-intensity protocol. Rest periods between sets were 4–6 min for both workouts. Blood samples were taken before, 30 min into, and every 15 min for the 1st h after exercise, and then 3, 7, 11, 22 and 33 h after exercise, thus allowing examination of both the acute and prolonged hormonal responses. Blood samples were analyzed for testosterone, luteinizing hormone (LH), follicle stimulating hormone (FSH), cortisol, adrenocorticotrophic hormone (ACTH), growth hormone (GH), insulin-like growth factor (IGF-1), insulin, sex hormone binding globulin, creatine kinase, total protein, glucose and lactate. The acute responses of testosterone and cortisol were greater during the high-intensity protocol as compared to the moderate-intensity protocol. The cortisol response was associated with an increase in ACTH concentration. LH and FSH showed no response to either protocol. Acute GH responses were not different between protocols. There were great inter-individual differences in acute GH responses to both protocols. There were no significant differences between protocols with regard to prolonged responses for any hormone. In both trials, IGF-1 concentrations were significantly lower at 0800 hours the morning after exercise as compared to concentrations found at 0800 hours the morning before exercise. The mechanisms responsible for reducing IGF-1 concentration in these trials are unclear, and it is not known if this reduction observed 22 hours after exercise is of physiological significance. Accepted: 13 December 1999     

Effects of exercise on vasodilatory capacity in endurance- and resistance-trained men

To determine vasodilatory responsiveness we measured forearm blood flow (FBF) following reactive hyperemia (RH), prior to and following a bout of maximal aerobic exercise in endurance- (n=14) and resistance-trained men (n=10). Both groups were similar in height, body mass, and percentage body fat. Using strain-gauge plethysmography, resting FBF was higher in the resistance-trained group [4.82 (0.84) vs 3.33 (1.17) ml min⁻¹ 100 ml⁻¹ of tissue; P<0.05]. However, the resistance-trained group had a 17%–29% lower pre-exercise FBF response to RH for the first 45 s (P<0.05). Following the maximal exercise bout there were no group differences in FBF. Post-exercise FBF was higher compared to pre-exercise values in both the endurance- (P<0.001) and resistance- (P<0.01) trained groups. Endurance-trained men appear to have a greater peak vasodilatory capacity compared to resistance-trained men, and acute maximal exercise increased the vasodilatory capacity in both groups. Acute exercise also equalized the peak vasodilatory response between the endurance- and resistance-trained groups, suggesting the potential for flow-mediated vasodilatation was similar for both groups. Electronic Publication     

Gross efficiency of muscular work during step exercise at -15°C and 21 °C

In an effort to assess the effect of ambient temperature on the gross efficiency (Eff_g) of step exercise 12 subjects performed a modified step test either at —15 °C or 21°C ascending to three different heights (corresponding to light, moderate and heavy work), for 20 min each with a frequency of 18 steps min^-1. Heart rate (HR), rectal temperature, skin temperatures and heat flux from skin were continuously measured. Oxygen consumption was measured during the last 5 min of each step height and perceptions of thermal sensation were recorded. The results indicate that, while using conventional clothing adequate in these temperatures, Eff_g is altered in a contradictory manner. At —15°C Eff_g increased with increasing work load, whereas at 21°C it decreased when the work load increased. The highest Eff_g (heavy work at —15°C and light work at 21°C) values are reflected as rather similar rectal temperatures (37.4–37.7°C) and identical mean skin temperatures (32.8 °C) as well as the same (slightly warm) thermal sensation of the legs. At — 15 °C the lowest Eff_g in light work was probably hue to the need to warm up the muscles. At 21°C, on the contrary, the activation of heat dissipation systems was probably responsible for the lowest Eff_g in heavy work.