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Summary: Seven trained male cyclists ( $$\dot V_{O_{2max} } $$ =4.420.23 lmin−1; weight 71.72.7 kg, mean SE) completed two incremental cycling tests on the cycle ergometer for the estimation of the “individual anaerobic threshold” (IAT). The cyclists completed three more exercises in which the work rate incremented by the same protocol, but upon reaching selected work rates of approximately 40, 60 and 80% $$\dot V_{O_{2max} } $$ , the subjects cycled for 60 min or until exhaustion. In these constant load studies, blood lactate concentration was determined on arterialized venous ([La−]av) and deep venous blood ([La−]v) of the resting forearm. The av-v lactate gradient across the inactive forearm muscle was −0.08 mmoll−1 at rest. After 3 min at each of the constant load work rates, the gradients were +0.05, +0.65* and +1.60* mmoll−1 (*P<0.05). The gradients after 10 min at these same work rates were −0.09, +0.24 and +1.03* mmoll−1. For the two highest work rates taken together, the lactate gradient was less at 10 min than 3 min constant load exercise (P<0.05). The [La−]av was consistently higher during prolonged exercise at both 60 and 80% $$\dot V_{O_{2max} } $$ than that observed at the same work rate during progressive exercise. At the highest work rate (at or above the IAT), time to exhaustion ranged from 3 to 36 min in the different subjects. These data showed that [La−] uptake across resting muscle continued to increase to work rates above the IAT. Further, the greater av-v lactate gradient at 3 min than 10 min constant load exercise supports the concept that inactive muscle might act as a passive sink for lactate in addition to a metabolic site.

Twitch potentiation was studied in the human triceps surae complex before and after intermittent maximal voluntary contractions or electrical stimulation at 20 Hz. Both forms of exercise were conducted with intact circulation for a maximum of 10 min or with circulatory occlusion until force output declined 50%. The relative potentiation was determined when a control twitch was compared to a twitch obtained after 5 s of maximal voluntary plantar flexion. The unpotentiated twitch torque (PT) and potentiated twitch torque (PT*) were reduced most severely after voluntary ischemic exercise (63.2% and 52.5% respectively, (P<0.001)). However, the relative potentiation (PT*/PT) immediately after voluntary ischemic exercise increased to 1.65±0.18 from 1.22±0.13 at rest. Both PT and PT* recovered quickly after exercise. At rest, twitch contraction time (CT) and one-half relaxation time (1/2 RT) in the unpotentiated twitch were longer than that of contraction (CT*) and one-half relaxation time (1/2 RT*) in the potentiated twitch. Following non-occluded exercise, CT, CT*, 1/2 RT and 1/2 RT* were shortened relative to rest. After ischemic exercise CT and CT* were shortened although 1/2 RT and 1/2 RT* increased relative to rest. Both CT* and 1/2 RT* quickly recovered to pre-exercise values by 5 min post-exercise. Ratios of potentiated/control twitch parameters were not altered after nonoccluded exercise, but were increased after ischemic exercise. These results suggest that the mechanisms of fatigue which depress voluntary torque and twitch and potentiated twitch torques, do not interfere with the extent of potentiation after fatiguing exercise.

Summary: The kinetics of oxygen uptake (VO2) were assessed in 17 normal subjects with Β-blockade and placebo. Β-blockade was achieved with either 50 mg oral metoprolol or 40 mg oral propranolol, each twice per day. Tests were conducted on the cycle ergometer at work rates approximating 80% of the work rate at ventilatory anaerobic threshold. Work rate was initiated as a square wave starting from prior rest. Data obtained 48 h, 1 week, and 4 weeks after starting drug or placebo were pooled to increase the number of points for regression analysis of kinetic parameters. While there were no differences in the plateau values for $$\dot V$$ O2 with and without Β-blockade, the rate of adaptation to steady state was significantly slower with Β-blockade than with placebo (p<0.05). This resulted in an increase of oxygen deficit by approximately 200 ml O2. Cardiac output measured by CO2 rebreathing was significantly reduced by Β-blockade (metoprolol by 4.1%, propranolol by 12.2%, both P<0.05). Blood lactate concentration was unaffected by Β-blockade. It was concluded that the influence of Β-blockade on the oxygen transport system was responsible for the significantly slower increase of $$\dot V$$ O2 to steady state in submaximal exercise.

Endocrine regulation of hormones and electrolytes during 37.5 h of -6° head down tilt (HDT) was studied in 13 men. The acute effects of simulated weightlessness are today well documented, but no study has been made concerning the hormone changes between 12 h and 2 days of HDT. Plasma volume showed a maximal increase of 9.23 (SEM 1.97) % after 6.5 h (P<0.01) and had returned to prestudy levels after 13.5 h of HDT. From 1.5 h to 4 h of HDT, C-terminus and N-terminus atrial natriuretic peptide (ANP) concentrations in plasma were increased by about 50% (P<0.01) and thereafter declined to pre-HDT levels. Plasma renin activity (PRA) was decreased by 47% (P<0.05) after 4 h of HDT; PRA increased after 23.5 h to 60%; noradrenaline concentration decreased immediately and remained low up to 37.5 h. Diuresis and natriuresis were evident during the 1st day of HDT, resulting in a marked increase in the urinary Na+. These results showed that the initial hormone (ANP, PRA) changes during HDT did not last more than 13.5 h and that after 24 h a new state would seem to have been established to adapt the body to hypovolaemia.

The effect of β-adrenergic blockade on the dynamic response characteristics of oxygen uptake was examined in seven healthy men. Cycle ergometer exercise consisted of a pseudorandom binary sequence (PRBS) with 15 units per sequence, each unit lasting 15 s, for a total period of 225 s. Work rate was either 25 W or 125 W. Six identical sequences were performed continuously in a single exercise test. Each subject was studied on three occasions after 48 h treatment of placebo (CON); a nonselective β-blocker, propranolol (PROP); and a β1-selective blocker, metoprolol (MET). was measured breath-by-breath. The data were analyzed in the frequency domain by Fourier analysis to yield amplitude and phase shift coefficients for the relationship between the input work rate and output . Time domain analysis was performed on the cross-correlational analysis of (output) · work rate (input) to determine the total lag time. The amplitude of the · W−1 relationship was lower (P<0.0022) and the phase shift was greater (P<0.0039) with β-blockade compared to CON; no differences were found between PROP and MET. The total lag time was longer (P<0.0053) in PROP (34.3±2.2s) and MET (34.4±1.6s) compared to CON (29.8±1.3s). These data indicate that β-adrenergic blockade causes a significant slowing of kinetics of the O2 transport system as determined by both frequency and time domain analysis. In addition, the PRBS exercise test is a sensitive indicator of change in function of the O2 transport system.

Summary: Internal mechanical work during cycling, required to raise and lower the legs and change their velocities, is shown to be an important factor when interpreting physiological responses to cycle ergometer exercise. The internal work required to move the legs during concentric and eccentric cycle ergometry at different speeds and workloads was calculated from segmental energy changes determined using cinematography and directly using an eccentric ergometer. The mean internal work rates obtained at pedal frequencies of 30, 60 and 90 min−1 were 11.5, 20 and 62 W respectively. When these estimates were added to the external work rates, they increased concentric and decreased eccentric work rates. The largest differences were seen at low work rates and high pedal frequencies during which concentric work rates increased by 51% and eccentric decreased 60% by the inclusion of internal work. When comparisons of concentric and eccentric cycling at equal uncorrected work rates were made, neglecting to include internal work introduced errors ranging from 12 to 97%. The calculated estimates of internal work agreed well with the power supplied by the eccentric ergometer to move the legs passively. The investigations show that the inclusion of internal work is important when comparing physiological responses during concentric and eccentric ergometry, especially when pedal frequences exceed 60 min−1 and when work rates are small.