The effect of induced alkalosis and acidosis on endurance running at an intensity corresponding to 4 mM blood lactate

Abstract

Short-term exercise is favourably affected by induced alkalosis and adversely affected by induced acidosis, although no study has examined these effects on prolonged high intensity exercise. This study examined the effects of induced alkalosis and acidosis on treadmill running at a velocity corresponding to a blood lactate concentration of 4mM (V-4mM).

The V-4mM was determined in seven healthy males using a continuous incremental test. Each subject then ran to exhaustion at an individually determined V-4mM on three separate occasions, following the ingestion of 0·2gkg body weight^?1 of either sodium bicarbonate (B), ammonium chloride (A) or sodium chloride (placebo, PL). Finger-prick blood samples were taken prior to ingestion, pre-exercise and post-exercise. The blood was analysed for pH, bicarbonate and lactate concentrations.

Treatment B produced a significant increase in blood pH and blood bicarbonate level (p<0·01) from pre-ingestion to pre-exercise, whereas A caused a significant decrease in blood pH and blood bicarbonate (p <0·01). No significant changes were obtained for PL (p>0·05). Pre-exercise blood pH and bicarbonate concentrations were significantly higher for B (p<0·01) and lower for A (p<0·01) than for PL.

Treatment B increased time to exhaustion by 17% (263 s) compared to PL, the direction of the change being positive in all subjects (p<0·01) when a non-parametric significance test was applied to the results. Treatment A significantly decreased time to exhaustion by 19% (295s) when compared to PL (p=0·05).

Post-exercise blood lactate concentrations were (9·17 ±4·46mM) for B, (7·79 ± 1·42 mM) for PL and (6·07 ± 1·61 mM)for A. None of these values were significantly different (p>0·05).

Results suggest that induced alkalosis has beneficial effects on prolonged, intense exercise whereas ammonium chloride adversely affects such performance, either by the induced acidosis or by the metabolic effects.     

The effects of gravity inversion on exercise-induced spinal loading

Abstract

Changes in stature reflect the creep behaviour of the intervertebral discs when loaded and unloaded. Running, weight-training and bounding are exercises which load the spine and cause a loss in stature. Gravity-facilitated traction (inversion) has been shown to unload the spine and increase stature. This study examined the use of a gravity-inverted posture for attenuating the shrinkage induced by a bounding exercise regimen.

Eight male subjects, aged 20–26, performed the experimental protocol twice, at the same time of day (14·00 hours) with an alteration only to their 10min pre-exercise behaviour. The first occasion involved standing and the second involved gravity inversion at an angle of 50 degrees to the vertical. Prior to testing, each subject stood for a period of 20 min. Measurements of stature were taken at the beginning of the experiment, before and after the pre-exercise treatments, after the exercise period and at 5 min intervals during a 20 min standing recovery. A stadiometer, accurate to within 0·5 mm, was used to record alterations in stature. The exercise regimen consisted often sets of five standing broad jumps with 15 s recovery between each set.

Standing pre-exercise caused little change in stature, whereas, gravity inversion caused a mean increase in stature of 2·7mm (p<0·001). Exercise caused a mean shrinkage of 1·7 mm and 3·5 mm when it followed standing and gravity inversion, respectively (p<0·05). These results suggest that the benefits gained by unloading the spine are short-lived.     

Influence of time of day and partial sleep loss on muscle strength in eumenorrheic females

Disrupted sleep is the most common form of sleep deprivation in travellers, shift workers, athletes the night before important competitions and among parents of infants. The influence of partial sleep loss on muscle strength might differ according to the time of testing on the following day. This study was therefore designed to assess the interaction between the effects of partial sleep loss and time of day on muscle strength in females. Eight sedentary eumenorrheic females (mean +/- SD; age 30 +/- 6 years, height 1.62 +/- 0.06 m and body mass 67 +/- 5.0 kg) took part in the study, in a counterbalanced design. Measurements of muscle strength were carried out at 06:00 and 18:00 hours after the one control night (no sleep loss) and the one night of partial sleep loss, during menses. Muscle strength measures included isokinetic (at 1.05, 3.14 rad s(-1); 90 degrees range of motion) and isometric peak torque (at 60 degrees of knee flexion) of knee extensors and flexors (dominant leg). In addition, isometric force of knee extensors with super-imposed electrical twitches (50 Hz, 250 V, 200 mus pulse width) was measured using the same procedure in order to control for motivation. Rectal temperature was measured during the 30 min before muscle strength measurements. Partial sleep loss consisted of allowing 2.5 h sleep (between 03:00 and 05:30 h), whilst in the control condition (no sleep loss) subjects retired between 22:30 and 23:30 h, rising at 05:30 hours. All measurements were conducted at just one phase of the menstrual cycle (menses) to prevent any masking effect due to different phases of the menstrual cycle. In both conditions (with and without partial sleep loss) a diurnal variation was observed in peak torque of knee flexors at 1.05 (F(1,7) = 5.5, p < 0.05) and 3.14 rad s(-1) (F(1,7) = 8.0, p < 0.05); values at 18:00 hours were 4.5 and 5.9% higher than at 06:00 hours, respectively. No significant diurnal variation was observed for the other muscle strength measures. No significant effect of partial sleep loss or interaction effect (sleep x time of day) was observed for muscle strength measures. However, the performance rhythms were in phase with the circadian rhythm in rectal temperature. Partial sleep deprivation over one night did not have any adverse effect on maximal muscle strength, nor on diurnal variations of muscle strength indices. As the effect of time of day was observed with some of the muscle strength measures, it is suggested that, in designing future studies using females, the control of time of day is essential.     

Dynamic control and conventional strength ratios of the quadriceps and hamstrings in subjects with anterior cruciate ligament deficiency

The hamstrings:quadriceps muscle strength ratio has been used as an indicator of normal balance between the knee flexors and extensors. A more functional approach to this strength ratio would be to compare opposite muscle actions of antagonistic muscle groups. The dynamic strength control ratio (DSCR) should give a more appropriate measure relating to knee function. There is a lack of normative data relating to DSCR for anterior cruciate ligament (ACL) deficient subjects. Effects of ACL deficiency on isokinetic peak torque for eccentric and concentric muscle actions of the quadriceps and hamstrings, in conjunction with isometric peak torque, were examined in 10 patients awaiting reconstructive surgery (male = 8, female = 2 ; age = 32.8 +/- 8.3 years; height = 1.77 +/- 0.08 m; mass = 72.1 +/- 12.5 kg). These variables were assessed using an isokinetic dynamometer. The results were considered in terms of the conventional ratio and DSCR. Anterior tibial drawer was measured using a knee ligament arthrometer to confirm clinical diagnosis of ACL rupture. The isokinetic peak torque data analysed were for angular velocities of 1.05 rad s(-1) (60 degrees s(-1)). Significant strength deficits were apparent between normal and injured sides for: concentric isokinetic quadriceps action (p < 0.05); isometric quadriceps action at 70 degrees of knee flexion (p < 0.05); isometric quadriceps action at 40 degrees of knee flexion (p<0.01); eccentric isokinetic hamstrings action (p < 0.05). With bilateral comparison, the conventional strength ratios showed no significant difference, as did the DSCR. The bilateral comparison of isometric strength ratios revealed significant losses in quadriceps strength for the injured side (p < 0.05) but no significant losses in hamstring strength (p > 0.05). Thus, differences can be seen in conventional ratios and DSCR for ACL-deficient subjects. This is an area of clinical interest with the increasing frequency of ACL reconstruction using hamstrings tendons.     

Re-entrainment of Body Temperature in Experimental Shift-Work Studies

In a series of experimental shift work studies six subjects worked on continuous night shift for three weeks, four subjects worked on a 1-1-1 shift system (1st day morning shift, 2nd day afternoon shift, 3rd day night shift, 4th day off), and two subjects worked on an 2-2-2 shift system (the ‘metropolitan rota’). Rectal temperature was continuously recorded in each experiment.

The greatest changes in the circadian rhythm of body temperature occurred on the second night shift day, and during the first week of continuous night shift working. The changes involved both shifts in the phasing of the rhythm, and alterations in its form. The re-entrainment of the rhythm to its normal phasing took two or more days after two or more successive night shifts, but only one day after a single night shift. Considerable individual differences in the rhythm adjustment to night work were observed.

In a field validation of these findings, 34 shiftworkers in municipal gas and water supply undertakings measured their oral temperature every 2h both on and off duty. Although only very few temperature readings were obtained during sleep periods, the results confirmed, in general, those of the experimental studies.     

The prediction of the adaptation of circadian rhythms to rapid time zone changes

The aim of the study was to find out which factors could explain individual differences in the resynchronization speed of circadian rhythms of salivary melatonin and subjective alertness after transmeridian flights over 10 time zones. The mean age of the 40 female subjects was 33·0 ±6·9 years. The data were gathered by measurements of the circadian rhythms of melatonin excretion and ahertness at 2 h intervals in Helsinki (Finland) two days before westward flight to Los Angeles (USA), where the measurements were repeated on the 2nd day after the flights and on the 2nd day in Finland after return flight. This shift in the acrophases of the two circadian rhythms were used as dependent variables in regression analyses. The predictors used were length of day, marital status, amount of physical exercise, age, neuroticism, extroversion, and eveningness. Age, day length, marital status, and physical exercise explained the acrophase adaptation of the melatonin rhythm after westward flight, and day length, neuroticism, and extroversion after eastward flight. Marital status, neuroticism, and physical exercise explained the variation of the acrophase adjustment of the alertness rhythm after westward flight, and age and eveningness after eastward flight. It is concluded that the amount of daylight and personality are the best predictors of the circadian rhythm adaptation after transmeridian flights.     

Dynamic control and conventional strength ratios of the quadriceps and hamstrings in subjects with anterior cruciate ligament deficiency

The hamstrings:quadriceps muscle strength ratio has been used as an indicator of normal balance between the knee flexors and extensors. A more functional approach to this strength ratio would be to compare opposite muscle actions of antagonistic muscle groups. The dynamic strength control ratio (DSCR) should give a more appropriate measure relating to knee function. There is a lack of normative data relating to DSCR for anterior cruciate ligament (ACL) deficient subjects. EVects of ACL deficiency on isokinetic peak torque for eccentric and concentric muscle actions of the quadriceps and hamstrings, in conjunction with isometric peak torque, were examined in 10 patients awaiting reconstructive surgery (male= 8, female= 2; age= 32.8 ± 8.3 years; height= 1.77 ± 0.08 m; mass= 72.1 ± 12.5 kg). These variables were assessed using an isokinetic dynamometer. The results were considered in terms of the conventional ratio and DSCR. Anterior tibial drawer was measured using a knee ligament arthrometer to confirm clinical diagnosis of ACL rupture. The isokinetic peak torque data analysed were for angular velocities of 1.05 rad s^?1 (60° s^?1). Significant strength deficits were apparent between normal and injured sides for: concentric isokinetic quadriceps action (p < 0.05); isometric quadriceps action at 70° of knee flexion (p < 0.05); isometric quadriceps action at 40° of knee flexion (p < 0.01); eccentric isokinetic hamstrings action (p < 0.05). With bilateral comparison, the conventional strength ratios showed no significant difference, as did the DSCR. The bilateral comparison of isometric strength ratios revealed significant losses in quadriceps strength for the injured side (p < 0.05) but no significant losses in hamstring strength (p > 0.05). Thus, differences can be seen in conventional ratios and DSCR for ACL-deficient subjects. This is an area of clinical interest with the increasing frequency of ACL reconstruction using hamstrings tendons.     

A Review of: “Influencing Organisational Change—The Role of the Personnel Specialist”. By CHARLES E. MARGHRISON. (London: Institute of Personnel Management, 1978.) [Pp. 219.] £5.25.

This study attempted to determine circadian rhythms in metabolic responses to submaximal and maximal workloads by concentrating on repeated observations of a male subject over 16 weeks. Altogether 36 experimental tests were undertaken on a cycle ergometer, six at each of the times, 0200, 0600, 1000, 1400, 1800 and 2200 hours. The work test comprised two consecutive 5-min periods at 82 and 147 W, followed immediately by an incremental workload to exhaustion. Significant circadian rhythms were found at rest pre-exercise for pulse rate (f_h), VO₂, V_E and rectal temperature (T_r) (p<0·001), with f_H leading the others in phase and T_t lagging significantly behind V_E (p<0·05). The circadian cycle in V_E persisted at both submaximal steady rates, with the VO₂ significant at the higher rate only when uncorrected for body weight. There was no evidence of a circadian variation in ‘muscular efficiency’. No significant rhythms were found in metabolic measures at maximal exercise or during recovery, indicating no time of day effect in the physiological capacity for exercise. The circadian variation in T_r persisted in phase and amplitude under maximal conditions and during recovery, indicating that the thermal load induced by a set exercise regime is independent of time of day.     

Changes in stature following plyometric drop-jump and pendulum exercises

The aim of this study was to compare the changes in stature following the performance of plyometric exercises using drop-jumps and a pendulum swing. Eight male participants aged 21.7 ± 1.8 years with experience of plyometric training gave their informed consent to act as participants. Participants undertook two exercise regimens and a 15-min standing test in a random order. The exercises entailed the performance of 50 drop-jumps from a height of 0.28 m or 50 pendulum rebounds. Participants were instructed to perform maximal jumps or rebounds using a ‘bounce’ style. Measurements of stature were performed after a 20-min period of standing (pre-exercise), 2-min after exercise (post-exercise) and after a 20-min standing recovery (recovery). Back pain and muscle soreness were assessed using an analogue-visual scale, at each of the above times and also 24 and 36 h after the test. Peak torque during isokinetic knee extension at 1.04 rads^?1 was measured immediately before and after the exercise bouts, to assess the degree of muscular fatigue. Ground/wall reaction force data were recorded using a Kistler force platform mounted in the floor for drop-jumps and vertically on the rebound wall for pendulum exercises. Drop-jumps resulted in the greatest (p<0.05) change in stature (-2.71±0.8 mm), compared to pendulum exercises (-1.77±0.7 mm) and standing (-0.39±0.2 mm). Both exercise regimens resulted in a significant (p<0.01) decrease in stature when compared to the standing condition. Dropjumps resulted in significantly greater peak impact forces (p<0.05) than pendulum exercises (drop-jumps = 3.2±0.5 × body weight, pendulum = 2.6±0.5×body weight). The two exercise conditions both invoked a small degree of muscle soreness but there were no significant differences between conditions. Both exercise regimens resulted in a non-significant decrease in peak torque indicating a similar degree of muscular fatigue. Based on the lower shrinkage resulted and lower peak forces, it can be concluded that pendulum exercises pose a lower injury potential to the lower back than drop-jumps performed from a height of 28 cm.     

Productivity on a weekly rotating shift system: circadian adjustment and sleep deprivation effects?

Abstract

There is little doubt that productivity and safety can be impaired on the night shift. Two main factors have been identified that may be responsible for this. On the one hand, the circadian rhythm in performance on at least simple tasks is at a low ebb at night, and adjusts only slowly over a span of night shifts. On the other, the day sleeps of shift workers taken between night shifts are of a reduced duration, and thus a cumulative sleep debt may accrue over successive night shifts. The former thus predicts that productivity should improve over a span of night duty, while the latter predicts that it should decline. We have examined the productivity of 53 female shift workers, and the sleeping habits of a sub-sample of 30 of them, on a weekly rotating shift system in order to assess the relative contribution of these two factors. Our results suggest that circadian adjustment to night work is the dominant factor for the first three or four successive nights shifts, but that sleep deprivation effects may then result in a decrease in productivity over subsequent nights. They also indicate that sleep deprivation, but not circadian adjustment, may affect the productivity of some workers when on the morning shift.     

Experimental Studies of Shift-Work II: Stabilized 8-hour Shift Systems

Abstract

Thirty-one subjects were employed in an experiment to determine whether the relationship between efficiency at mental tasks and the circadian rhythm of body temperature observed in an earlier study was affected by an increase in the length of the duty-spell from 4 to 8 hours. Subjects wore assigned either to a control ‘ day ’ shift (O800–1600), a ‘ night ’ shift (2200–0600) or a ( morning ) shift (0400–1200), and were tested for a period of 12 consecutive days on the same shift. The control shift-workers showed no consistent effects of fatigue due to the increased length of the duty-spell. Adaptation of temperature rhythm to work on the night shift was only partial, but was relatively closely reflected in the recorded performance trends. Very little adaptation to work on the morning shift was observed, and performance was thought to have been affected by partial sleep deprivation. It was concluded that body-temperature was as effective a predictor of overall mental efficiency in most industrial-type shifts as in the special 4-hour shift system previously investigated.     

Gender differences in the circadian variations in muscle strength assessed with and without superimposed electrical twitches

The circadian rhythm in muscle strength was analysed in 12 males (28 +/- 4 years, 79.6 +/- 12.3 kg, 1.80 +/- 0.05 m) and eight females (28 +/- 4 years, 60.3 +/- 5.5 kg, 1.61 +/- 0.08 m). After two familiarization sessions, participants were tested at six different times of the day (02:00, 06:00, 10:00, 14:00, 18:00 and 22:00 hours), the order of which was randomly assigned over 3-4 days. Rectal temperature (T(rec)) was measured over 30 min before each test. Peak isokinetic torques (PT) of knee extensors and flexors were then measured at 1.05 rad s(-1) and 3.14 rad s(-1) through a 90 degrees range of motion. Maximal isometric voluntary contraction (MVC) of knee extensors and flexors was measured at 60 degrees of knee flexion and the MVC of knee extensors was also assessed with superimposed electrical twitches (50 Hz, 250 V, 200 mus pulse width) in order to control for motivational effects. Three trials were performed in each condition, separated by 3 min recovery, and the highest values were retained for subsequent analyses. A significant circadian rhythm was observed for T(rec) in both males and females (acrophase, Phi, 17:29 and 16:40 hours; mesor, Me, 37.0 and 36.8 degrees C; amplitude, A, 0.28 and 0.33 degrees C for males and females, respectively). The mesor of T(rec) was higher in males than in females (p < 0.05). Significant circadian rhythms were observed for knee extensor PT at 3.14 rad s(-1) in males (Phi, 17:06 hours; Me, 178.2 N m; A, 4.7 N m) and for knee extensor PT at 1.05 rad s(-1) in females (Phi, 15:35 hours; Me, 128.7 N m; A, 3.7 N m). In males, the MVC of knee extensors demonstrated a significant circadian rhythm, but only when electrical twitches were superimposed (Phi, 16:17 h; Me, 302.1 N m; A, 13.6 N m). Acrophases of all indices of muscle strength were not statistically different between the two groups and were located in the afternoon (12:47 < Phi < 17:16 hours). The amplitude (percentage of mesor) of extensors MVC (electrically stimulated) was higher in males (6.4%) than in females (4.2%; p < 0.05). Significant circadian rhythms were not consistently observed for all indices of muscle strength whatever the gender. Our group of female subjects tended to show lower circadian amplitudes than the males. In males, maximal voluntary contraction of electrically stimulated muscles followed a circadian curve, which was not significant without the superimposed twitches. These results suggest that motivation could have a masking effect on the circadian rhythm in muscle performance and strengthen the view that peripheral factors are implicated in this rhythm.     

Effect of temporal patterns of work on lifting and handling capacities

Lifting and handling involve complex movements with concentric, isometric and eccentric muscle contractions. Greatest force deployment is attained in eccentric contractions, and in these the force increases with speed. The elastic energy stored in an eccentrically contracting muscle remains during a short time available for a subsequent concentric contraction. A kinesiological analysis of the centre of gravity and the mass centres of body segments make it possible to define the centres of motion and their movement, and further, the changes of velocity during contacts and the acting forces. The contributions of various' muscle elements can be described with electromyography     

Correlation dimension analysis of heart rate variability in patients with dilated cardiomyopathy

A correlation dimension analysis of heart rate variability (HRV) was applied to a group of 55 patients with dilated cardiomyopathy (DCM) and 55 healthy subjects as controls. The 24-h RR time series for each subject was divided into segments of 10,000 beats to determine the correlation dimension (CD) per segment. A study of the influence of the time delay (lag) in the calculation of CD was performed. Good discrimination between both groups (p<0.005) was obtained with lag values of 5 or greater. CD values of DCM patients (8.4+/-1.9) were significantly lower than CD values for controls (9.5+/-1.9). An analysis of CD values of HRV showed that for healthy people, CD night values (10.6+/-1.8) were significant greater than CD day values (9.2+/-1.9), revealing a circadian rhythm. In DCM patients, this circadian rhythm was lost and there were no differences between CD values in day (8.8+/-2.4) and night (8.9+/-2.1).     

The influence of irregularity of rest and activity on performance: a model based on time since sleep and time of day

Abstract

Changes in performance during a 9 day period of an irregular schedule of work and rest were investigated. Performance varied with the circadian rhythm and the length of the work periods. For the majority of subjects these two factors were additive. The time-of-day variation was well approximated by a sinusoid and the time-since-sleep factor was represented by a cubic trend. The acrophase of the circadian rhythm varied throughout the experiment under the influence of the sleep-wake cycle and the time-of-day cues. A model which included time of day and time since sleep was used to predict variations in performance for work periods starting at different times of the day. It is considered that this model can be applied to current issues in the scheduling of civil airline pilots’ duty periods.     

Inversion of the Sleep Wakefulness Pattern: Effects on Circadian Variations in Psychophysiological Activation

Abstract

Thirty-six habitually dayworking railway repairmen were exposed to a 3 week period of nightwork. The subjects were studied with respect to circadian rhythms in catecholamine excretion, body temperature, subjective alertness and mood. For half the group the measurements covered one 24 h period before nightwork, the first week of night work, the third week of night work, and the first week after return to day work. For the other half measurements were made during the first and third day week after the night work. During day work weeks all variables exhibited pronounced circadian variation, peaking in the early afternoon, with the exception of body temperature which reached its maximum in the evening. During the first week of night work the day-oriented pattern of adrenaline excretion persisted but the mean 24 h level was increased and day sleep levels were very high. By the third week of night work thecircadian pattern had flattened out at a very low mean level. For noradrenaline excretion considerable adjustment (comparable to an inversion) to night work was seen with high night values. For body temperature, selfrated alertness and mood circadian functions flattened out during night work. It was concluded that all variables were strongly affected by the exposure to night work and that adrenaline excretion indicated a stress response of the organism. With reference to other studies it was also concluded that adrenaline excretion is not easily phase-shifted through a three week spell on night work, while noradrenaline in contrast appears to adjust very rapidly.     

Static and dynamic lifting strength at different reach distances in symmetrica] and asymmetrical planes

Postural and therefore biomechanical standardization in strength testing has not been rigorously and consistently applied. To develop a quantitative relationship between strength and posture (body position, symmetry, and reach) 30 normal subjects (18 male and 12 females) were required to stoop and squat lift or exert in the relevant posture against a standardized instrumented handle. The isometric lifting efforts and isokinetic lifts were studied. The isokinetic lifts were done at a linear velocity of 50cm/s of the hand displacement from the floor to the knuckle heights of the respective subjects in stoop and squat postures. The isometric stoop lifting efforts were exerted in two standardized postures: (a) with 60° hip flexion; and (b) with 90° hip flexion. The isometric squat lifting efforts were also exerted in two standardized postures: (a) with 90° knee flexion; and (b) with 135° knee flexion. All isometric lifting efforts and isokinetic lifts were performed at half, three-quarters, and full horizontal reach in sagitally symmetrical, 30° left lateral, and 60° left lateral planes. Isometric stoop and squat lifting efforts were also measured in self-selected optimal postures. These 56 conditions were tested in random order. The analysis of variance revealed that the gender, the mode of lifting, the postural asymmetry and reach of lifting affected the strength significantly (p<0·0001). Most two-way and three-way interactions were significant (p<0·01). Of 108 prediction regression equations, 103 were significant with up to 90% of the variation explained by anthropometric variables and sagittal plane strength. The reach affected the strength most profoundly followed by postural asymmetry and the mode of lifting.     

The effect of four-day round trip flights over 10 time zones on the circadian variation of salivary melatonin and Cortisol in airline flight attendants

The effects of four-day round flights (Helsinki-Los Angeles-Seattle-Helsinki) were studied on the circadian rhythms of salivary melatonin (MT) and Cortisol (COR) in 35 flight attendants. The mean age of the subjects was 33 ± 7 years (median 34, range 21-50). Five 24 h profiles of unstimulated saliva were collected at 2 h intervals (except at 04:00) before, during, and after the four day flight. Salivary MT and COR were determined by radioimmunoassay. Both MT and COR exhibited a clear circadian rhythm with acrophases before the flight at 03:03 (MT) and 09:08 (COR). Two days after the westward flight from Helsinki to Los Angeles, the MT rhythm (circadian acrophase) had delayed 4 h 51 min and the COR rhythm 3 h 55 min compared to the control day before the flight. Two days later, during the last day in the USA, the MT rhythm had delayed 5 h 59 min and the COR rhythm 5 h 29 min as compared to the situation before the flight. After four days of the eastward flight from Seattle to Helsinki, the circadian acrophase of MT was still 1 h 35 min delayed compared to the control day before the westward flight. The results indicate that the restitution time of five days at the home base is on the average proper for recovery, if a four day round flight over 10 time zones takes four days or less. The resynchronization rate of salivary hormones after westward, outgoing flights is faster than the resynchronization rate after the eastward return flights.     

Sleep deprivation,chronic exercise and muscular performance

Muscular performance was tested during 64 hours of sleep deprivation with and without intermittent excercise (treadmill walking at 28% of maximum oxygen intake). The subjects (12 males aged 22·7 ± 2·2 years) carried out a cross-over trial with an 8 week interval separating the two periods of sleep deprivation. The sleep deprivation did not change the time for a 40 m dash, isometric handgrip force or balance (stabilometer test). Vertical jump height decreased, the change being significant for simple sleep deprivation, but not for the combination of deprivation and intermittent exercise. Sleep deprivation decreased isokinetic extension force at 60° s?1, while intermittent walking decreased isokinetic extension force at both 60 and 180° ?1; however, there was no significant difference between exercise plus sleep deprivation and sleep deprivation alone at either angular velocity. We conclude that the moderate intensity of physical activity likely in industrial work has little influence upon human performance under conditions of sleep deprivation.     

Ageing, physical fitness and shiftwork tolerance

The effects of ageing and physical fitness on shiftwork tolerance are reviewed. Ageing is one of the most cited factors decreasing the health of shiftworkers. Although long-term prospective studies on ageing are few, shiftworkers over 40-45 years of age seem to sleep worse after night, but not after morning shifts. Sleepiness after successive night shifts is also decreased by age although older shiftworkers' ability to resist acute sleep loss seems to be even better. The reasons for the altered sleep and wakefulness of older shiftworkers are probably related to changes in circadian rhythms, especially higher 'morningness'. Sleep need may also decrease with age which could explain some of the differences found in sleep length. Physical fitness as a factor increasing tolerance to shiftwork is a recent finding. Although the effects of physical activity on sleep have been studied in detail, the relationship of physical fitness to sleep is still a controversial issue. In shiftworkers, moderate physical training has been shown to increase sleep length and night-time alertness. It has not been shown, however, that exercise would quicken the circadian adjustment to night work. It is recommended that work time arrangements should take account of the older workers' changing personal references. Continuous night work should be voluntary after 40 years of age. Moderate physical exercise a few hours before the main sleep period is recommended.