Adenine nucleotide and IMP contents of the quadriceps muscle in man after exercise

Subjects performed submaximal and maximal bicycle exercise. Work time was between 2 and 15 min. Muscle biopsies were taken from m. quadriceps femoris at rest, immediately after termination of exercise and in some cases during the recovery period. Samples were analyzed for lactate, ATP, ADP, AMP, inorganic phosphate, creatine phosphate, creatine and IMP. The decrease in creatine phosphate and ATP/ADP ratio, as well as the increase in lactate were similar to previous investigations. Total adenine nucleotide content (TAN=ATP+ADP+AMP) decreased after maximal exercise with about 15% but was unchanged after submaximal exercise. The decrease in TAN after maximal exercise was corresponded by a similar increase in muscle IMP content. After 30 min of recovery TAN was restored to the basal value and IMP had decreased correspondingly. The physiological importance of adenine nucleotide degradation and IMP accumulation is discussed as well as the regulatory properties of the involved enzymes. The amount of energy which is liberated when 1 mol of ATP is hydrolysed to ADP has been calculated to decrease from 54 kJ at rest to 50 kJ after exhaustive exercise. It is suggested that the energy yield in the hydrolysation of ATP, rather than the amount of available ATP, is limiting for muscle contraction.     

Lactate concentrations in human skeletal muscle biopsy, microdialysate and venous blood during dynamic exercise under blood flow restriction

The intramuscular microdialysate lactate concentration during dynamic exercise with various degrees of blood flow restriction and its relation to lactate concentration in skeletal muscle biopsy and venous blood were studied. Nine healthy males performed three one-legged knee extension exercises (Ex 1–3). Blood flow was restricted stepwise by applying supra-atmospheric pressure over the working leg. Microdialysate mean (range) lactate concentrations at the end of the exercise periods were 3.2 (0.5–6.6), 4.4 (1.1–9.8) and 7.9 (1.1–11.6) mmol·l^–1 during unrestricted, moderately restricted and severely restricted blood flow respectively. There was a significant correlation between microdialysate and venous lactate concentrations at the end of all three exercise periods. Microdialysate lactate concentration correlated significantly to skeletal muscle biopsy lactate concentration at the end of Ex 1. In conclusion, microdialysate lactate concentration in the working muscle increased step-wise with increasing blood flow restriction. It showed a better correlation to venous than to muscle biopsy lactate, which is possibly partly explained by the characteristics of diffusion between body compartments and differences in time resolution between the methods used.An erratum to this article can be found at     

Lactate after exercise in man: I. Evolution kinetics in arterial blood

Summary Arterial and venous blood lactate concentrations were measured at 10 or 30 s time intervals before, during, and after several types of muscular exercise on an ergocycle in a sitting or supine position. Arterial blood lactate concentration curves over the recovery period were found to fit a biexponential time function including a rapidly increasing and a slowly decreasing component, even during active recovery at approximately 40% max exercise. The velocity constants were dependent on the exercise load. They were also linearly related to each other. The time of lactate disappearance during recovery increased with the work load.     

Lactate after exercise in man: IV. Physiological observations and model predictions

Summary Following earlier papers that established the mathematical form of the time dependence of lactate concentrations during recovery from several types of exercise, and that set up a two-compartment model predicting the same time dependences, the present work applies the model to obtain parameters of specific physiological processes. Satisfactory agreement between predictions of the model and our experiment and literature data is obtained in the cases where comparisons can be made, as in the muscular lactate time evolution measured from biopsy samples, in blood flows through the active muscle at the end of exercise or at rest and their evolution during recovery, as well as in the volume of the active muscle compartment. The model prediction that lactate efflux from the muscles to the blood can reduce to zero during recovery is verified experimentally.List of Abbreviations and Symbols A ₁, A ₂ Amplitudes of the two exponential terms fitted to arterial lactate concentrations (mol·1^–1) - ₁₂, ₂₁ Transfer coefficients from (M) to (S) and (S) to (M) respectively (min^–1) - A _D Area of the body according to Dubois (m²) - BM Body mass (kg) - C ₁, C ₂ Amplitudes of the exponential terms of L _m (t) (mol·1^–1) - c ₁, d ₁ Rates of lactate production in (M) and (S), respectively (mol·min^–1) - c ₂, d ₂ Coefficients of lactate disappearance in (M) and (S) respectively (min^–1) - F ₁ Field of validity of the model (see [32]) - ₁, ₂ Velocity constants of the exponential terms fitted to arterial lactate concentrations (min^–1) - L _a (t) Arterial lactate concentration at time t (mmol·1^–1 or mol·1^–1) - L _a max Maximum arterial lactate concentration of the recovery (mmol·1^–1) - L _fv (t) Femoral venous blood lactate concentration at time t (mmol·^–1) - L _M (t), L _S (t) Lactate concentrations in (M) and (S), respectively at time t (mmol·1^–1 or mol·1^–1) - (M) Working or active muscle space - q(t) Blood flow through (M) at time t (ml·100 ml^–1·min^–1) - _MS (t) Rate of net lactate release from (M) to (S) at time t (mmol·min^–1) - Rate of net lactate release from (M) to (S) at t(mol·min^–1) - (S) Remaining lactate space - t Time after the end of exercise (min) - , Moments at which the net lactate release from (M) to (S) becomes zero (min) - ₂ Moment of the intersection of the arterial and brachial venous blood lactate curves (min) - _fa1, _fa2 Moments of the intersection of the arterial and femoral venous blood lactate curves (min) - V _M , V _s , V _TLS Volume of (M), (S), and (TLS), respectively, [1] - (TLS) Total lactate space - Difference between L _M () and L _s ()     

On muscle strength and the threshold of anaerobic work

Summary 1.When subjects are exercised on a bicycle ergometer at 80% of aerobic power, there is a progressive increase of arterial lactate for 5–15 min, and in subjects of poor cardio-respiratory fitness the terminal level may approach that found in maximal exercise. 2. 5 min of sub-maximal exercise at 70 or 80% of aerobic power leads to a substantial accumulation of arterial lactate (38.3±8.9, 47.6±8.9 mg/100 ml) respectively. 3. The arterial lactate levels following 5 min of sub-maximal exercise are negatively correlated with the strength of hand-grip and knee extension. 4. Evidence is presented that lactate accumulation represents an effect of muscle contraction on oxygen supply rather than an overloading of intracellular biochemical mechanisms. 5. Perceived exertion in sub-maximal exercise is related to pulse rate as previously described byBorg. However, it is not related to arterial lactate or sensitivity to thermal stress.     

Glycolytic intermediates in human muscle after isometric contraction

Isometric contraction of the quadriceps muscle sustained to fatigue with a force of 66% of the maximum voluntary contraction force resulted in a mean glycogen utilization of 80.4 (S.D. 58.4) mmol glucosyl units/kg dry muscle (d.m.) and an accumulation of glycolytic intermediates and glucose corresponding to 82.9 (S.D. 17.5) mmol glucosyl units/kg d.m. Accumulation of hexose phosphates (principally glucose 6-phosphate) accounted for 35.4% (S.D. 4.1) of the total increase and lactate for 59.3% (S.D. 2.8). During a 4 min recovery period glucose 6-[hosphate content showed a linear decrease with a half time of 2.0 min and lactate decreased exponentially with a half time of 2.5 min. The rate of lactate disappearance from the muscle was approximately 4 times as fast as that observed previously after maximal bicycle exercise. This was probably due to a lower lactate concentration in blood after isometric contraction resulting in a larger muscle-blood gradient for lactate. Muscle content of free glucose was increased after contraction and increased further during recovery. It is concluded that the glucose increase is confined to the intracellular pool and is an effect of hexokinase inhibition by accumulated glucose 6-phosphate. Occlusion, of the local circulation after the contraction inhibited the recovery processes for lactate and glucose 6-phosphate.     

Lactate disposal in resting trained and untrained forearm skeletal muscle during high intensity leg exercise

Summary At a given oxygen uptake ( O₂) and exercise intensity blood lactate concentrations are lower following endurance training. While decreased production of lactate by trained skeletal muscle is the commonly accepted cause, the contribution from increased lactate removal, comprising both uptake and metabolic disposal, has been less frequently examined. In the present study the role of resting skeletal muscle in the removal of an arterial lactate load (approximately 11 mmol·-l^–1) generated during high intensity supine leg exercise (20 min at approximately 83% maximal oxygen uptake) was compared in the untrained (UT) and trained (T) forearms of five male squash players. Forearm blood flow and the venoarterial lactate concentration gradient were measured and a modified form of the Fick equation used to determine the relative contributions to lactate removal of passive uptake and metabolic disposal. Significant lactate uptake and disposal were observed in both forearms without any change in forearm O₂. Neither the quantity of lactate taken up [UT, 344.2 (SEM 118.8) mol·100 ml^–1; T, 330.3 (SEM 85.3) mol·100 ml^–1] nor the quantity disposed of [UT, 284.0 (SEM 123.3) mol·100 ml^–1, approximately 83% of lactate uptake; T, 300.8 (SEM 77.7) mol·100 ml^–1, approximately 91% of lactate uptake] differed between the two forearms. It is concluded that while significant lactate disposal occurs in resting skeletal muscle during high intensity exercise the lower blood lactate concentrations following endurance training are unlikely to result from an increase in lactate removal by resting trained skeletal muscle.     

Back extensor muscle oxygenation and fatigability in healthy subjects and low back pain patients during dynamic back extension exertion

The purpose of this study was to assess if chronic low back pain patients have impaired paraspinal muscle O₂ turnover and endurance capacity as compared to healthy control subjects during dynamic exercise. Middle-aged healthy male subjects (n = 12, control) and male patients with chronic low back pain (n = 17, CLBP) participated in the study. L4–L5 level paraspinal muscle fatigue was objectively assessed during earlier validated 90 s dynamic back endurance test (spectral EMG, MPF_slope). Also EMG amplitude (EMG_amplitude) and initial MPF (MPF_initial) were assessed from the initial 5 s of the endurance contraction. Simultaneously near infrared spectroscopy (NIRS) was used for quantitative measurement of local L4–L5 paraspinal muscle O₂ consumption. Subcutaneous tissue thickness (ATT) was measured from the EMG and NIRS recording sites. The results indicated that control and CLBP groups were compatible as regarding anthropometric variables, paraspinal muscle activation levels (EMG_amplitude), initial MPF (MPF_initial) and ATT. When the ATT was used as a covariate in the ANOVA analysis, CLBP group did not show significantly greater paraspinal muscle fatigability (right MPF_slope – 12.2 ± 10.7%/min, left right MPF_slope – 12.6 ± 13.3%/min) or O₂ consumption (right NIRS_slope – 52.8 ± 79.6 μM/l/s) as compared to healthy controls (right MPF_slope – 11.9 ± 7.6%/min, left MPF_slope – 12.7 ± 8.6%/min, right NIRS_slope – 53.7 ± 95.2 μM/l/s). As a conclusion, these CLBP male patients did not show any impaired rate of paraspinal muscle oxygen consumption or excessive paraspinal muscle fatigability during dynamic exercise as compared with healthy controls. Subcutaneous tissue thickness has a strong influence on the NIRS and EMG amplitude measurements and, if unchecked, it could result in the false interpretation of the results.     

High-intensity exercise decreases muscle buffer capacity via a decrease in protein buffering in human skeletal muscle

We have previously reported an acute decrease in muscle buffer capacity (βm_{in vitro}) following high-intensity exercise. The aim of this study was to identify which muscle buffers are affected by acute exercise and the effects of exercise type and a training intervention on these changes. Whole muscle and non-protein βm_{in vitro} were measured in male endurance athletes (VO_2max = 59.8 ± 5.8 mL kg⁻¹ min⁻¹), and before and after training in male, team-sport athletes (VO_2max = 55.6 ± 5.5 mL kg⁻¹ min⁻¹). Biopsies were obtained at rest and immediately after either time-to-fatigue at 120% VO_2max (endurance athletes) or repeated sprints (team-sport athletes). High-intensity exercise was associated with a significant decrease in βm_{in vitro} in endurance-trained males (146 ± 9 to 138 ± 7 mmol H⁺·kg d.w.⁻¹·pH⁻¹), and in male team-sport athletes both before (139 ± 9 to 131 ± 7 mmol H⁺·kg d.w.⁻¹·pH⁻¹) and after training (152 ± 11 to 142 ± 9 mmol H⁺·kg d.w.⁻¹·pH⁻¹). There were no acute changes in non-protein buffering capacity. There was a significant increase in βm_{in vitro} following training, but this did not alter the post-exercise decrease in βm_{in vitro}. In conclusion, high-intensity exercise decreased βm_{in vitro} independent of exercise type or an interval-training intervention; this was largely explained by a decrease in protein buffering. These findings have important implications when examining training-induced changes in βm_{in vitro}. Resting and post-exercise muscle samples cannot be used interchangeably to determine βm_{in vitro}, and researchers must ensure that post-training measurements of βm_{in vitro} are not influenced by an acute decrease caused by the final training bout.     

Gentle exercise with a previously inactive muscle group hastens the decline of blood lactate concentration after strenuous exercise

Summary The aim of this study was to elucidate the mechanism by which the disappearance of blood lactate following severe exercise is enhanced during active recovery in comparison with recovery at rest. Rates of decline of arterialised venous blood lactate concentrations in man after maximal one-leg exercise were compared during four different modes of recovery: passive (PR), exercise of the muscles involved in the initial exercise (SL), exercise of the corresponding muscles in the hitherto-inactive leg (OL), or exercise of one arm (RA). Recovery exercise workloads were each 40% of the onset of blood lactate accumulation (OBLA) for the limb used. In comparison with PR, SL and OL accelerated the fall in blood lactate to similar extents whereas RA was without effect. The first-order rate constant (min^–1) for decline of arterialised venous blood lactate concentration after the intense exercise was 0.027 (0.003) in PR, 0.058 (0.025) in SL, 0.034 (0.002) in OL, and in RA was 0.028 (0.002) [mean (SEM),n = 6 subjects]. Preliminary studies had shown that RA in isolation elevated blood lactate whereas SL and OL did not. Thus, with appropriate workloads, exercise of either hitherto active or passive muscles enhanced blood lactate decline during recovery from intense exercise. This suggests that the effect resulted principally from the uptake and utilisation of lactate in the circulation by those exercising muscles rather than from increased transport of lactate to other sites of clearance by sustained high blood flow through the previously active muscles.     

Lactate kinetics during passive and partially active recovery in endurance and sprint athletes

We investigated the effects of passive and partially active recovery on lactate removal after exhausting cycle ergometer exercise in endurance and sprint athletes. A group of 14 men, 7 endurance-trained (ET) and 7 sprint-trained (ST), performed two maximal incremental exercise tests followed by either passive recovery (20 min seated on cycle ergometer followed by 40 min more of seated rest) or partially active recovery [20 min of pedalling at 40% maximal oxygen uptake ( O_2max) followed by 40 min of seated rest]. Venous blood samples were drawn at 5 min and 1 min prior to exercise, at the end of exercise, and during recovery at 1, 2, 3, 4, 5, 6, 8, 10, 15, 20, 30, 40, 50, 60 min post-exercise. The time course of changes in lactate concentration during the recovery phases were fitted by a bi-exponential time function to assess the velocity constant of the slowly decreasing component (₂) expressing the rate of blood lactate removal. The results showed that at the end of maximal exercise and during the 1st min of recovery, ET showed higher blood lactate concentrations than ST. Furthermore, ET reached significantly higher maximal exercise intensities [5.1 (SEM 0.5) W · kg^–1 vs 4.0 (SEM 0.3) W · kg^–1,P < 0.05] and O_2max [68.4 (SEM 1.1) ml · kg^–1 · min^–1 vs 55.5 (SEM 5.1) ml · kg^–1 · min^–1,P < 0.01]. There was no significant difference between the two groups during passive recovery for ₂ During partially active recovery, ₂ was higher than during passive recovery for both groups (P < 0.001), but ET recovered faster and sooner than ST (P < 0.05). Compared to passive recovery, the ₂ measured during partially active recovery was increased threefold in ET and only 1.5-fold in ST. We concluded that partially active recovery potentiates the enhanced ability to remove blood lactate induced by endurance training.     

The blood pressure response during isometric exercise in fast and slow twitch skeletal muscle in the cat

Summary The blood pressure response during fatiguing isometric contractions was examined in a slow twitch muscle (the soleus) and a mixed muscle (the medial gastrocnemius) of the cat. The results of these experiments showed that electrical stimulation of the ventral roots of the spinal cord which carried the efferent innervation to the soleus muscle failed to result in a blood pressure response during isometric exercise. Further, although stimulation of the fast twitch motor units in the medial gastrocnemius muscle was associated with a potent pressor response to isometric exercise, stimulation of the slow twitch motor units was associated with a markedly reduced response throughout the duration of the exercise. These findings infer that the pressor response to isometric exercise may be a function of the fast twitch motor units in the muscle.     

The time course of phosphorylcreatine resynthesis during recovery of the quadriceps muscle in man

Summary The time course of phosphorylcreatine (PC) resynthesis in the human m. quadriceps femoris was studied during recovery from exhaustive dynamic exercise and from isometric contraction sustained to fatigue. The immediate postexercise muscle PC content after either form of exercise was 15–16% of the resting muscle content. The time course of PC resynthesis during recovery was biphasic exhibiting a fast and a slow recovery component. The half-time for the fast component was 21–22 s but this accounted for a smaller fraction of the total PC restored during recovery from the isometric contraction than after the dynamic exercise. The half-time for the slow component was in each case more than 170 s. After 2 and 4 min recovery the total amounts of PC resynthesized after the isometric exercise were significantly lower than from the dynamic exercise.Occlusion of the circulation to the quadriceps completely abolished the resynthesis of PC. Restoration of resynthesis occurred only after release of occlusion.     

Formation of acetylcarnitine in muscle of horse during high intensity exercise

Summary To study the changes in carnitine in muscle with sprint exercise, two Thoroughbred horses performed two treadmill exercise tests. Biopsies of the middle gluteal were taken before, after exercise and after 12 min recovery. Resting mean muscle total carnitine content was 29.5 mmol · kg⁻¹ dry muscle (d. m.). Approximately 88% was free carnitine, 7% acetylcarnitine and acylcarnitine was estimated at 5%. Exercise did not affect total carnitine, but resulted in a marked fall in free carnitine and almost equivalent rise in acetylcarnitine. The results are consistent with a role for carnitine in the regulation of the acetyl-CoA/CoA ratio during sprint exercise in the Thoroughbred horse by buffering excess production of acetyl units.     

Plasma norepinephrine and heart rate dynamics during recovery from submaximal exercise in man

Summary The time course of heart rate (HR) and venous blood norepinephrine concentration [NE], as an expression of the sympathetic nervous activity (SNA), was studied in six sedentary young men during recovery from three periods of cycle ergometer exercise at 21%±2.8%, 43%±2.1% and 65%±2.3% of respectively (mean±SE). The HR decreased mono-exponentially withτ values of 13.6±1.6 s, 32.7±5.6 s and 55.8±8.1s respectively in the three periods of exercise. At the low exercise level no change in [NE] was found. At medium and high exercise intensity: (a) [NE] increased significantly at the 5th min of exercise (Δ[NE]=207.7±22.5 pg·ml⁻¹ and 521.3±58.3 pg·ml⁻¹ respectively); (b) after a time lag of 1 min [NE] decreased exponentially (τ=87 s and 101 s respectively); (c) in the 1st min HR decreased about 35 beats · min⁻¹; (d) from the 2nd to 5th min of recovery HR and [NE] were linearly related (100 pg·ml⁻¹ Δ[NE]5 beats ·min⁻¹). In the 1st min of recovery, independent of the exercise intensity, the adjustment of HR appears to have been due mainly to the prompt restoration of vagal tone. The further decrease in HR toward the resting value could then be attributed to the return of SNA to the pre-exercise level.     

The effect of one-legged sprint training on intramuscular pH and nonbicarbonate buffering capacity

Summary To determine the effect of one-legged sprint training on muscle pH and nonbicarbonate buffering capacity (BC), 9 subjects completed 15 to 20 intervals at 90 RPM, 4 days a week for 7 weeks on a bicycle ergometer adapted for one-legged pedaling. Needle biopsies from the vastus lateralis and blood samples from an antecubital vein were taken at rest and twice during recovery (1 and 4 minutes) from a 60 s one-legged maximal power test on a cycle ergometer. pH one minute after exercise in both the trained and untrained legs following the training period was not different but both were higher than before training. BC increased from 49.9 to 57.8 mol HCl×g^–1×pH^–1 after training (p<0.05). Blood lactate levels after exercise were significantly higher for the trained leg when compared to the untrained leg after sprint training. Peak and average power output on the 60 s power test increased significantly after training. One-legged aerobic power ( ) significantly increased in the untrained and trained legs. Two-legged also improved significantly after training. These data suggest that nonbicarbonate buffering capacity and power output can be enhanced with one-legged sprint training. Also, small but significant improvements in were also observed.     

Resistance exercise increases postexercise oxygen consumption in nonexercising muscle

This study examined the effect of knee extension resistance exercise on muscle oxygen consumption in nonexercising forearm flexor muscles after exercise. Seven healthy male subjects were performed six sets of unilateral knee extension exercise until exhaustion at 40, 60, and 80% of 1 repetition maximum (RM) on separate days. The values at rest, at the end of exercise, and during recovery after exercise were measured by near-infrared spectroscopy. The at the end of exercise was significantly (P < 0.05) increased by 1.8 ± 0.2, 1.7 ± 0.2, and 1.4 ± 0.3 fold over resting value at 40, 60 and 80% 1RM, respectively. returned to the resting values after 1–5 min of recovery and then showed no further significant change for all exercise intensities. This study suggests that knee extension resistance exercise at 40, 60 and 80% 1RM induced an increase in and that the increase of after exercise returned to resting value in several minutes.     

Skeletal muscle phosphagen and lactate concentrations in ischaemic dynamic exercise

Summary Five young males performed dynamic, submaximal contractions to exhaustion with the quadriceps muscle under arterial occlusion. The work load was 14.7 Watt (W). After 10 min rest with intact arterial circulation, the subjects commenced another bout to exhaustion; this process was repeated until a total of 10–16 bouts had been performed. Muscle biopsies were obtained immediately after the second, fifth, eighth, and last bout as well as 30 min after the last bout. The concentrations of adenosine triphosphate (ATP), creatine phosphate (CP), lactate, and glycogen were measured in each sample and some material underwent histochemical analysis. Muscle lactate was highest following the second work bout [22.9 mmol/kg wet weight (ww)] and gradually declined to 7.0 mmol/kg ww by the end of the last bout. CP level was low in all postexercise samples with the exception of a remarkably high CP (11.7 mmol/kg ww) after the last bout. Glycogen utilization tended to parallel muscle lactate levels, the rate of depletion being most rapid initially. Histochemical staining for glycogen depletion revealed that both type I and II fibres were low in glycogen, although type I was depleted most uniformly. In the first work bouts the high lactate and low CP levels in the total muscle could be responsible for the fatigue; none of these factors seem adequate to explain the development of the fatigue experienced in the later work bouts. It is concluded that muscle fatigue in this type of exercise is not related to substrate depletion or accumulation of metabolites, further that the fibre recruitment pattern is determined by the type and relative severity of performed work rather than local metabolic factors.Supported by grants from the Danish National Association Against Rheumatic Diseases and the Danish Council for Sports Research     

The interrelationship between blood pressure,intramuscular pressure,and isometric endurance in fast and slow twitch skeletal muscle in the cat

Summary Two series of experiments were performed to examine the interrelationships between blood pressure, intramuscular pressure, muscle blood flow, and the endurance for isometric exercise in a fast (medial gastrocnemius) and a slow (soleus) twitch muscle of the cat. In the first series of experiments, the relationship between tension and intramuscular pressure was examined. It was found that intramuscular pressure was linearly related to tension in both muscles. However, at any proportion of the muscles maximum tension, the intramuscular pressure of the medial gastrocnemius muscle (the stronger of the muscles) was about twice that of the soleus. A second series of experiments was conducted in which blood pressure was increased above intramuscular pressure and the effect of blood pressure on isometric endurance was measured. The pressure of the perfusing blood of the cat's hind limb was adjusted to either 13.3, 26.6, or 39.9 kPa. It was found that increased perfusion of the muscle resulted in a dramatic increase in the endurance for contractions sustained at isometric tensions below 60% of the muscle's initial strength. In contrast, for contractions above this tension, the effect of increased perfusion was much less pronounced.