Electrically evoked contractions of the triceps surae during and following 21 days of voluntary leg immobilization

Summary The effects of 21 days voluntary leg (plaster) immobilization on the mechanical properties of the triceps surae have been studied in 11 young female subjects, mean age 19.4 years. The results show that during the period of immobilization the mean time to peak tension (TPT) and half relaxation time (1/2RT) and tension (P_t) of the maximal twitch increased significantly (p<0.001) but the effects were short lived. Maximal tension and contraction times of the twitch recovered within 2–14 days following the removal of the plaster cast. The electrically evoked tetanic tensions at 10 Hz and 20 Hz did not change significantly (p>0.1) during immobilization, but the 50 Hz tetanic tension (P_°50) and maximal voluntary contraction (MVC) were reduced (p<0.05). The fall in P_°50 and MVC was associated with 10% decrease in the estimated muscle (plus bone) cross-sectional area. The relative (%) change in P_°50 and MVC following immobilization was related to the initial physiological status (as indicated by the response of the triceps surae to a standard fatigue test prior to immobilization) of the muscle. The rate of rise and recovery fall of the tetanus were slightly but significantly (p<0.01) reduced on day 7 of immobilization, but thereafter remained constant. The isokinetic properties of the triceps surae as reflected in the measured torque/velocity relation of the muscle in 4 subjects did not change significantly if account was taken of the slight degree of atrophy present following immobilization. It was concluded that short term voluntary leg immobilization produces atrophy and some loss of isometric twitch and tetanic function, but has little effect on the isokinetic properties of the triceps surae. The changes in the twitch characteristics during and immediately following immobilization may be indicative of a prolongation of the active state of the muscle.     

Muscle activation and the isokinetic torque-velocity relationship of the human triceps surae

Summary The influence of muscle activation and the time allowed for torque generation on the angle-specific torque-velocity relationship of the triceps surae was studied during plantar flexion using supramaximal electrical stimulation and a release technique on six male subjects [mean (SD) age 25 (4) years]. Torque-velocity data were obtained under different levels of constant muscle activation by varying the stimulus frequency and the time allowed for isometric torque generation prior to release and isokinetic shortening. To eliminate the effects of the frequency response on absolute torque the isokinetic data were normalized to the maximum isometric torque values at 0.44 rad. There were no significant differences in the normalized torques generated at any angular velocity using stimulus frequencies of 20, 50 or 80 Hz. When the muscle was stimulated at 50 Hz the torques obtained after a 400 ms and 1 s pre-release isometric contraction did not differ significantly. However, with no pre-release contraction significantly less torque was generated at all angular velocities beyond 1.05 rad · s^–1 when compared with either the 200, 400 ms or 1 s condition. With a 200 ms pre-release contraction significantly less torque was generated at angular velocities beyond 1.05 rad · s^–1 when compared with the 400 ms or 1 s conditions. It would seem that the major factor governing the shape of the torque-velocity curve at a constant level of muscle activation is the time allowed for torque generation.     

The effects of two forms of isometric training on the mechanical properties of the triceps surae in man

The training effects of rhythmic and sustained isometric contractions on the contractile characteristics of the triceps surae have been investigated in four healthy subjects over a period of 8 weeks. One leg (ST) of each subject was trained by performing repeated daily sustained (1 min) isometric contractions at 30% of maximal voluntary contraction force (MVC), and the other using rhythmic isometric contractions at 100% of MVC. The protocol was so arranged that the total area under the training force/ time curves was the same for each limb. Electrically evoked maximal twitch (P _t) and tetanic (P _o) tensions of the triceps surae were measured weekly on both legs using a standard procedure.The results showed that the rhythmic regime increased the MVC at the rate of 5.5% per week and the sustained training increased MVC at the rate of 3.3% per week. Twitch and tetanic tensions were not altered by either regime. However, only training using sustained contractions produced a progressive increase in endurance as measured by performance in a fatigue test.The results suggest that increases in voluntary strength resulting from short term isometric training are not necessarily associated with a rise in the intrinsic involuntary capacity of muscle fibres to generate force.     

A comparison of voluntary and electrically evoked isokinetic plantar flexor torque in males

Summary The angle-specific isokinetic torque- and power-velocity relationships of the triceps surae were examined in ten male sprint athletes aged [mean (SD)] 22.4 (3.2) years, ten non-trained adult men aged 27.4 (4.8) years and six elderly male subjects aged 68.5 (2.4) years. Normal voluntary contractions were compared with those obtained using maximal tetanic stimulation and a release technique which standardised the level of muscle activation during isokinetic contractions. When the isokinetic data was normalized to the maximum isometric torque the stimulated release contractions at 5.18–5.29 rad · s^–1 produced significantly (P < 0.05) greater torque than the voluntary no-release contractions at the same angular velocity in each group of subjects. The three subject groups generated their peak power at 3.07 rad · s^–1 during the voluntary no-release contractions. However, with the stimulated release contractions, power had still not reached a peak at 5.29 rad · s^–1, the highest angular velocity that could be tested. It appears that at higher angular velocities the triceps surae is capable of greater torque and power generation when contractions are evoked using a stimulated release technique. It is suggested that the stimulated release technique gives a more complete picture of the torque-velocity characteristics of the contractile component of the triceps surae.     

Muscular fatigue during repeated isokinetic shoulder forward flexions in young females

Summary Peak torque, work, mean power and electromyographic (EMG) activity were recorded for each of 150 repeated isokinetic maximal shoulder flexions (45°–90°) in 23 healthy females. From the EMG signals of trapezius, deltoid, infraspinatus and biceps brachii the mean power frequency and the signal amplitude were determined in real time. The mechanical output showed a steep decrease during the first 40 contractions, followed by a plateau maintained until the end. In all muscles, except the biceps brachii, significant decreases in mean power frequency occurred during the first 40 contractions, showing a tendency to stabilize around the same absolute frequency value. Signal amplitude increased in the trapezius, the deltoid and the infraspinatus, but was constant in the biceps brachii. For some individuals rather high EMG activity was recorded in the muscles during the time the arm was supposed to be passively extended to the starting position, and this was found to be associated with lower strength and endurance levels. Longitudinal analyses showed that the mean power frequencies correlated better than the signal amplitudes with the three mechanical variables. The results suggest that the initial steep decrease in mechanical performance and mean power frequency is caused by fatiguing of type 2 motor units.     

Effect of isometric and isokinetic muscle training on static strength and dynamic power

Summary This study investigated whether isokinetic strength training might induce changes in static and dynamic power already achieved as a result of isometric strength training. The subjects were twelve males. The isometric strength and dynamic power of elbow flexors were tested by means of an electric dynamometer and fly-wheel every two weeks. During the first 8 weeks all subjects trained the elbow flexors isometrically at four different positions of elbow joints. This training produced 27–36% gains in isometric strength and 34–46% in power. Thereafter the subjects were divided into two groups: the FG group who trained isokinetically at a fast velocity of 157·s^–1, and the SG group at slow velocity of 73·s^–1. After 6 weeks of training, the FG group produced a significant gain in power with light equivalent masses and the SG group did so with heavy equivalent masses. Neither group showed change in isometric strength.     

Electrically evoked torque-velocity characteristics and isomyosin composition of the triceps surae in young and elderly men

The electrically evoked isokinetic torque-velocity relationship of the triceps surae of eight elderly and four non-trained young men was examined in relation to the isomyosin composition of the soleus and the gastrocnemius muscles, determined under non-denaturing conditions using pyrophosphate gel electrophoresis. The angle specific torque-velocity properties of the triceps surae were measured using maximal percutaneous electrical stimulation at 50 Hz and a release technique. The elderly subjects generated significantly (P < 0.05) less absolute torque at all angular velocities when compared with the young subjects. When the isokinetic data were normalized to the isometric torque, the lower normalized torques generated by the elderly subjects were not statistically different from the young. The total fast isomyosin (FM) content of the soleus and gastrocnemius in the elderly subjects was 22 ± 13 and 35 ± 18%, respectively. This compared with 29 ± 8 (n.s.) and 44 ± 8% (n.s.) in the young subjects. When the gastrocnemius and soleus muscles were given an equal weighting and considered together to represent the whole triceps surae, the normalized torque at the fixed angular velocity of 5 rad s^-1 was significantly associated with%FM (r = 0.90, P < 0.01), and the isomyosin bands%FM1 (r = 0.90, P < 0.01) and%FM2 (r = 0.93, P < 0.001) when only the elderly subjects were considered. No relationships were observed between contractile characteristics and contractile protein profile when only the young subjects were considered. This was despite the inclusion of a further two sprint and three endurance trained athletes to increase the range of contractile characteristics and differences in muscle composition.     

Computer analysis of the surface EMG during isometric exercise

A computer program is described which can provide either on-line or off-line analysis of the surface electromyogram (EMG) in man during submaximal isometric contractions. The intention of the program was to quantify the tension developed by, and the degree of fatigue induced in muscle during this form of exertion from the surface EMG. Six male and female volunteers served as subjects to test the program by exerting brief isometric contractions of their handgrip muscles at tensions ranging from 3 to 100% of their maximum strength and fatiguing isometric contractions at tensions ranging between 20 and 95% of their maximum strength. The results of these experiments showed that the program was able to estimate the tension developed by muscle within an average of 2.4% of the subject's maximum strength and estimate the duration of fatigue contractions within an average of 3.5% of the actual recorded endurance. The applications of this form of analysis to work physiology are discussed.     

Blood flow in the triceps brachii muscle in humans during sustained submaximal isometric contractions

The main purpose of this study was to determine the extent to which blood flow through the profunda artery within the triceps brachii muscle may be compromised during maintained low-force isometric fatiguing contractions. Doppler ultrasound techniques were used to record mean blood velocity and arterial diameter of the profunda brachii artery during sustained isometric contractions of 20% maximal voluntary contraction. The arterial diameter did not change throughout the contraction. Thus, blood velocity was considered to be an indicator of blood flow. The mean blood velocity increased initially and then remained constant during the contraction period. When compared to rest [0.06 (SD 0.03) m s^–1] mean blood velocity was significantly larger at the start of the contraction [0.13 (SD 0.07) m s^–1] and larger yet during recovery following the contraction [0.30 (SD 0.14) m s^–1]. Although blood flow through the conduit artery did not drop during the contraction, the post-contraction hyperaemia suggested that circulatory compromise might have occurred at the level of the capillary beds. Electronic Publication     

The relationship between muscle myosin ATP-ase activity and isometric endurance in untrained male subjects

Summary The influence of variations in muscle fibre composition on isometric endurance capacity was measured in 23 young healthy untrained male volunteers. After determination of the maximum voluntary force of contraction (MVC), subjects sustained to fatigue contractions at forces of 80%, 50% and 20% of MVC with a 5-min rest between each. A needle biopsy was obtained from m. vastus lateralis and used for histochemical determination of fibre composition based on myosin ATP-ase activity, and fibre are a based on succinate dehydrogenase (SDH) activity. Endurance times were 21±9 s (mean±SD) at 80% of MVC, 56±17 s at 50% of MVC and 203±89 s at 20% of MVC. A wide range of muscle fibre compositions was observed with Type I fibres accounting for 48.0±10.5% of the total, corresponding to 45.0±11.5% of the total muscle area. Muscle fibre composition, whether expressed as the proportions of the different fibre types present, or as the fraction of total muscle cross-sectional area occupied by each fibre type was not correlated with isometric endurance capacity at any of the three forces studied. Endurance time was also unrelated to MVC. In contrast to the results of previous studies where trained subjects were used, or where different muscle groups were compared, these results suggest that isometric endurance is not influenced by muscle fibre composition.     

Metabolic and cardiorespiratory responses to maximal intermittent knee isokinetic exercise in young healthy humans

There have been many studies on the effects of isokinetic exercise on muscle performance in training and rehabilitative programmes. On the other hand, the cardiovascular and metabolic responses elicited by this type of exercise have been poorly investigated. This study was specifically designed to describe the relationships, if any, between metabolic and cardiorespiratory responses and power output during maximal intermittent knee isokinetic exercise when a steady state is reached. A group of 18 healthy subjects (10 men and 8 women, age range 25–30 years) were requested to perform at maximal concentric isokinetic knee extensions/flexions 60° · s⁻¹ and 180° · s⁻¹ for 5 min, with a 5-s pause interposed between consecutive repetitions. The power output (W˙) was calculated; before and during the tasks heart rate (f _c) and arterial blood pressure (AP_a) were continuously monitored. Pulmonary ventilation (V˙ _E) and oxygen uptake (V˙O₂) were measured at the 4th and at the 5th min of exercise and blood lactate concentration at rest and at the 3rd min of recovery. From the 4th to the 5th min only a slight decrease in W˙ was observed, both at 60° · s⁻¹ and 180° · s⁻¹. The V˙O₂, V˙ _E, f _c and AP_a showed similar values in the last 2 min of exercise, suggesting that a steady state had been reached. The V˙O₂ increased linearly as a function of W˙, showing a significantly steeper slope at 60° · s⁻¹ than at 180° · s⁻¹. The f _c, in spite of a large interindividual variation, was linearly related to metabolic demand, and was not affected by angular velocity. Systolic and diastolic AP_a were not related either to V˙O₂ or to angular velocity. In conclusion it would appear that the metabolic response to maximal intermittent knee isokinetic exercise resembles that of dynamic exercise. Conversely, the cardiocirculatory responses would seem to reflect a relevant role of the isometric postural component, the importance of which should be carefully evaluated in each subject. Accepted: 21 September 1999     

Twitch contractile adaptations are not dependent on the intensity of isometric exercise in the human triceps surae

Summary Ultrastructural and twitch contractile characteristics of the human triceps surae were determined in six healthy but very sedentary subjects before and after 16 weeks of isometric training at 30% maximal voluntary contraction (MVC). Following training, twitch contraction time was approximately 16% shorter, although no differences were observed in one-half relaxation time or peak twitch torque. Percent fibre type was not changed by training. The mean area of type I and type II fibres in the soleus increased by approximately 30% but only type II fibres showed an increase in area in the lateral gastrocnemius (30%). Despite such changes in fibre area the volume density of the sarcoplasmic reticulum-transverse tubular network averaged 3.2 ± 0.6% and 5.9 ± 0.9% in type I and type II fibres respectively, before and after training in the two heads of the gastrocnemius. The results indicate that contractile adaptations to isometric training at 30% MVC were limited to twitch contraction time and were not directly related to changes in percent fibre distribution or the volume of sarcoplasmic reticulum and transverse tubules in either type I or type II fibres. The data further demonstrate that substantial fibre hypertrophy is achieved by training with low-intensity contractions.     

Contractile properties of the human triceps surae muscle during simulated weightlessness

The effect of a 120-day period of bed rest on the mechanical properties of human triceps surae muscle was studied in a group of male volunteers (n = 6, mean age 38 years). The results shows that the contractile properties of skeletal muscle in response to disuse change considerably. Time to isometric peak tension of the triceps surae muscle increased from 120 (SEM 3.0) ms to 136 (SEM 2.9) ms (P < 0.01), half relaxation time from 92 (SEM 2.1) ms to 100 (SEM 1.6) ms (P < 0.05) and total contraction time from 440 (SEM 9.9) ms to 540 (SEM 18.7) ms (P < 0.001). Isometric twitch force (F _t) decreased by a mean of 36.7% (P < 0.05), maximal voluntary contraction (MVC) and maximal force (F _max) by a mean of 45.5% and 33.7%, respectively (P < 0.05-0.01). The valueF _max:F _t ratio increased by 3.6% (nonsignificant). The difference betweenF _max and MVC, expressed as a percentage ofF _max and referred to as force deficiency, has also been calculated. Force deficit increased by a mean of 60% (P < 0.001) after bed rest. Force-velocity properties of the triceps surae muscle calculated according to an absolute scale of voluntary and electrically evoked contraction development decreased considerably. The calculations of the same properties on a relative scale did not differ substantially from the initial physiological state. The results would suggest that muscle disuse is associated with both atrophy and a reduction in contractility in the development ofF _max and decreased central (motor) drive. The change in the triceps surae muscle contractile velocity properties may indicate changes in the kinetically active state in the muscles.     

Quadriceps muscle function characteristics in severely obese and nonobese adolescents

The purpose of this cross-sectional study was to compare quadriceps muscle strength and fatigue between severely obese (body mass index 34 kg/m²) and nonobese adolescents. Maximal isokinetic torque and angle of peak torque as well as isometric torque at short (40° of knee flexion) and long (80° of knee flexion) muscle length were measured using an isokinetic dynamometer. Muscle fatigue was quantified as the percent torque loss during an isokinetic voluntary protocol and an electrical stimulation isometric protocol. Obese adolescents produced greater absolute isokinetic (+16%; P < 0.05) and isometric torque at short (+25%; P < 0.01) but not at long muscle length (P > 0.05) compared to their lean counterparts. The angle of peak torque was significantly lower in obese than in nonobese subjects (−11%; P < 0.05), i.e., obese produced their maximal strength at shorter muscle length. Isokinetic and isometric torque normalized to the fat-free mass were not significantly different between the two groups. No significant difference in voluntary and stimulated torque loss was observed between groups. Muscle strength per unit of fat-free mass and muscle fatigue were similar in the obese and nonobese adolescents tested in this study, therefore suggesting that obesity has little or no effect on quadriceps muscle function characteristics. On the other hand, it remains to be confirmed whether the observed quadriceps muscle length specificity contributes to the reduced functional capacity of obese adolescents during complex motor tasks involving deep knee flexion (squatting, kneeling).     

Comparison of the histochemical and contractile properties of human triceps surae

The purpose of the study was to compare the contractile properties determined from an electrically stimulated twitch with histochemically determined fibre type parameters of the human triceps surae. Muscle samples were obtained from the medial head of the gastrocnemius of ten male athletes. Ages ranged from 20 to 29 years. Muscle samples from the belly of the medial gastrocnemius muscle were obtained using the needle biopsy technique. The samples were treated histochemically for myosin ATPase to classify the fibres as either slow twitch (ST) or fast twitch (FT) and to determine fibre areas. Surface electrical stimulation was used to determine muscle twitch parameters. The contractile variables of the muscle twitch were latency (L), time to peak force (TPF), peak force (PF), half-contraction time (1/2 CT) and half-relaxation time (1/2 RT). Backward elimination procedures for dependent variables were used to determine which contractile properties best represented the histochemical profile of the muscles. Prediction formulas were developed for FT and ST percentages (R²=0·98, p<0·001), relative area percentage (R²=0·87, p<0·001), and ST area (R²=0·85, p<0·01). It was concluded that the use of the electrotensiometer (ETM) protocol was a valid testing procedure when studying physiological relationships of histochemical properties in intact human skeletal muscle. Protected by patent no. 4 688 581.     

Effects of 17-day spaceflight on electrically evoked torque and cross-sectional area of the human triceps surae

The effects of spaceflight on triceps surae muscle torque and cross-sectional area (CSA) were investigated on four astronauts using electrically evoked contractions to by-pass neural control. Muscle twitch characteristics, ankle joint angle–twitch torque relation, frequency–torque relation, tetanic torque and fatigability were assessed before, during and after a 17-day Space Shuttle flight (STS-78). Muscle plus bone cross-sectional area (CSAm+b) was evaluated before and after the flight. Whereas no changes in muscle function were observed during the flight, marked alterations were found during the recovery period. Peak twitch (PTw) and tetanic torques at 50 Hz (PT₅₀) continued to fall up to the 8th recovery day (R+8) on which losses in PTw and PT₅₀ were 24.4% (P<0.01) and 22.0% (P<0.01), respectively. The decline in PTw was not joint-angle-specific. Post-flight, especially on R+8, torque decreased at all stimulation frequencies (1, 20, 30 and 50 Hz); however the shape of the frequency–torque curve, normalised for PT₅₀, was not modified. Similarly, no changes in twitch kinetics were observed. Post- flight, an 8% (P<0.01) reduction in CSAm+b was found on R+2. Normalisation of PT₅₀ values for CSAm+b showed a progressive loss in specific torque (PT₅₀/CSAm+b), which was maximal on R+2 (19.5%, P<0.05). Also, fatigability during 2-min intermittent stimulation at 20 Hz increased throughout recovery, reaching a nadir of 16.4% (P<0.01) on R+15. In conclusion, 17 days of spaceflight resulted in significant changes in muscle function during the recovery phase, but not in microgravity. The disproportionate loss of torque compared with that of muscle size suggests the presence of muscle damage due to reloading in 1 g.     

The pressor response to voluntary and electrically evoked isometric contractions in man

Summary Blood pressure and heart rate changes during sustained isometric exercise were studied in 11 healthy male volunteers. The responses were measured during voluntary and involuntary contractions of the biceps brachii at 30% of maximal voluntary contraction (MVC), and the triceps surae at 30% and 50% MVC. Involuntary contractions were evoked by percutaneous electrical stimulation of the muscle.Measurements of the time to peak tension of maximal twitch showed the biceps brachii (67.0±7.9 ms) muscle to be rapidly contracting, and the triceps surae (118.0±10.5 ms) to be slow contracting. The systolic and diastolic blood pressures increased linearly throughout the contractions, and systolic blood pressure increased more rapidly than diastolic. There was no significant difference in response to stimulated or voluntary contractions, nor was there any significant difference between the responses to contractions of the calf or arm muscles at the same relative tension.In contrast the heart rate rose to a higher level (P<0.01) in the biceps brachii than the triceps surae at given % MVC, and during voluntary compared with the electrically evoked contractions in the two muscle groups.It was concluded that the arterial blood pressure response to isometric contractions, unlike heart rate, is primarily due to a reflex arising within the active muscles (cf. Hultman and Sjöholm 1982) which is associated with relative tension but independent of contraction time and muscle mass.     

Effect of prior exercise at different pedalling frequencies on maximal power in humans

Summary The effect of prior submaximal exercise performed at two different pedalling frequencies, 60 and 120 rev · min^–1, on maximal short-term power output (STPO) was investigated in seven male subjects during cycling exercise on an isokinetic cycle ergometer. Exercise of 6-min duration at a power output equivalent to 92 (SD 5)% maximal oxygen uptake , whether performed at a pedalling frequency of 60 or 120 rev · min^–1, reduced maximal STPO generated at 120 rev · min^–1 to a much greater extent than maximal STPO at 60 rev · min^–1. After 6-min submaximal exercise at 60 rev · min^–1 mean reductions in maximal STPO measured at 120 and 60 rev · min^–1 were 27 (SD 11)% and 15 (SD 9)% respectively, and were not significantly different from the reductions after exercise at 120 rev · min^–1, 20 (SD 13)% and 5 (SD 9)%, respectively. In addition, we measured the effect of prior exercise performed at the same absolute external mechanical power output [236 (SD 30)W] with pedalling frequencies of 60 and 120 rev · min^–1, Although the external power output was the same, the leg forces required (absolute as well as expressed as a proportion of the maximal leg force available at the same velocity) were much higher in prior exercise performed at 60 rev · min^–1. Nevertheless, maximal STPO generated at 120 rev · min^–1 was reduced after exercise at 120 rev-min^–1 [20 (SD 13) %,P<0.05] whereas no significant reduction in maximal STPO was found after prior exercise at 60 rev · min^–1. The present findings would suggest that exercise performed at 92 (SD 5)% , whether at 60 or at 120 rev · min^–1, selectively fatigues the faster fatigue-sensitive fibres resulting in a greater reduction in maximal STPO generated at 120 compared to 60 rev · min^–1. The greater fatigue of maximal STPO generated at 120 rev · min^–1 due to exercise performed at a power output of 236 (SD 30)W at 120 rev · min^–1 compared to 60 rev · min^–1 would suggest a relatively greater contribution of fast fatigue-sensitive fibres when higher movement frequencies and hence different muscle shortening velocities are used at this submaximal exercise intensity.     

Control of the recruitment and firing frequencies of motor units in electrically stimulated muscles in the cat

Although the order by which motor units are recruited, and the frequencies at which they fire, vary during different types of exercise, laboratory studies involving the electrical stimulation of muscle have never examined the effect of different orders of recruitment on muscular function. This has been due, principally, to the lack of an adequate technique capable of selectively stimulating discrete populations of motor units in a muscle having a mixed population of fibres. The paper describes a computer-controlled stimulator and special electrode array which can control the pattern of motor-unit recruitment during electrical stimulation of the lower leg of the cat. In addition, following a program of recruitment analogous to that which is believed to normally occur during voluntary isometric exercise, the computer was able to sustain isometric muscular contractions to fatigue at a variety of tensions with almost identical endurance times. as are found in man.     

Maximal mechanical power output and capacity of cyclists and young adults

Summary The maximal average power output ( ) has been examined in 10 male students, 22 pursuit and 12 sprint cyclists. In 24 of these subjects (8 students, 10 pursuit and 6 sprint cyclists), estimates of the maximal capacity ( ) of the short-term anaerobic energy yielding processes were made. The results show that the sprinters had a higher absolute (1241±266 W) and (16.7±4.9 kJ) than either the students (1019± 183 W, 14.7±2.8 kJ) or the pursuit cyclists (962±206 W, 14.0±2.9 kJ). However, the differences were removed when the values were standardised for muscle size. In the sprinters theW _max was attained at an optimal pedal frequency of 132±3 min⁻¹ and the estimated maximal velocity of pedalling ( ) was 262±8 min⁻¹. The comparable figures in the students and pursuit cyclists were 118±8 min⁻¹, 235±17 min⁻¹ and 122±6 min⁻¹, 242±12 min⁻¹ respectively. The coefficient of variation of duplicate measurements of was found to be ±9%. Using data of Wilkie (1968) for muscle phosphagen and glycolytic stores (27 mmol · kg⁻¹), it was estimated that the probable efficiency of the anaerobic processes during maximal cycling was 0.22. It was concluded that and are largely determined by body size and muscularity. The efficiency of anaerobiosis appears to be of the same order of magnitude as found for oxidative work.