Temperature and neuromuscular function.

This review focuses on the effects of different environmental temperatures on the neuromuscular system. During short duration exercise, performance improves from 2% to 5% with a 1 °C increase in muscle temperature. However, if central temperature increases (i.e., hyperthermia), this positive relation ceases and performance becomes impaired. Performance impairments in both cold and hot environment are related to a modification in neural drive due to protective adaptations, central and peripheral failures. This review highlights, to some extent, the different effects of hot and cold environments on the supraspinal, spinal and peripheral components of the neural drive involved in the up- and down-regulation of neuromuscular function and shows that temperature also affects the neural drive transmission to the muscle and the excitation-contraction coupling.

Lung function after acute and repeated exposures to extremely cold air (-110 degrees C) during whole-body cryotherapy.

Whole-body cryotherapy (WBC) is one mode of cold therapy, during which rheumatic patients are exposed to very cold air (-110 degrees C) in minimal clothing. It is also proposed to have a bronchodilatory effect. The aim was to examine the effects of WBC on lung function in healthy humans after acute and repeated exposures. Twenty-five healthy, non-smoking subjects participated in the study. They were exposed to WBC for 2 min three times per week for 12 weeks. The peak expiratory flow rate (PEF) and forced expiratory volume in 1 s (FEV1) were measured before and after (at 2 and 30 min) the first WBC, and then similarly at 4, 8 and 12 weeks. At all time points, after 30 min of the WBC the PEF values were slightly lower compared with values before the WBC, and the reductions reached statistical significance at 1 month (5.1 +/- 1.2%), and at 3 months (3.2 +/- 1.7%). After 30 min of the first WBC, the FEV1 was significantly reduced by 2.3 +/- 0.8%, but no other changes were observed during the study. In conclusion, the WBC induced minor bronchoconstriction in healthy humans instead of proposed bronchodilatation. The WBC seems not to be harmful for lung function, but should be used with caution in susceptible individuals.

Cooling-induced changes in muscular performance and EMG activity of agonist and antagonist muscles.

The effect of whole body cooling on the muscular performance and electromyographic (EMG) activity of agonist and antagonist muscles during dynamic exercise was studied. Eleven slightly clothed male subjects were exposed to ambient temperatures of 27 degrees C and 10 degrees C for 60 min. After the exposures the subjects performed an overhead ball throwing test. Five balls, weighing from 0.3 kg to 3.0 kg were thrown and the velocity of the balls was measured. The EMG activity of two agonist-antagonist muscle pairs (m. triceps brachii--m. deltoideus and m. rectus abdominis--m. erector spinae) were measured during throwing. Cooling decreased mean skin temperature by 6.3 +/- 0.5 degree C (mean +/- SE). The temperature of m. triceps brachii decreased by 4.0 +/- 1.6 degrees C and 1.8 +/- 0.6 degrees C from the depth of 20 and 30 mm underneath the skin surface, respectively. The corresponding values of m. deltoideus were 5.1 +/- 0.4 degrees C and 3.2 +/- 0.8 degrees C. The cooling-induced decrement in ball velocity varied from 9.4 +/- 3.3% (0.3-kg ball) to 5.6 +/- 2.8% (3.0-kg ball) (p < 0.001-0.01). After cooling, the time to reach the maximal level of integrated electromyographic (IEMG) activity in m. triceps brachii (agonist) was increased (30-42%, p < 0.05-0.001). Moreover, cooling decreased the mean IEMG activity m. triceps brachii, while the activity of m. deltoideus (antagonist) was increased. The alteration was significant (p < 0.05-0.001) with the three lightest balls.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle strain during aerial combat maneuvering exercise.

BACKGROUND: Little is known about the in-flight muscular strain of fighter pilots. HYPOTHESIS: The purpose of this study was to measure fighter pilots' mean and peak muscular strain during aerial combat maneuvering exercises. The results obtained were compared against existing ergonomic recommendations. METHODS: Six pilots volunteered to serve as test subjects. Their mean age (+/- SD) was 28.5 +/- 5 yr, height 181 +/- 7 cm, and weight 75 +/- 10 kg. They performed one-to-one dog-fight exercises in the morning and in the afternoon. During the flights, the pilots' electromyographic activity (EMC) was measured from the thigh, abdomen, back, and lateral neck. The mean and peak muscular strain for each muscle was calculated as the percentage of maximal voluntary contraction (%MVC). RESULTS: The results showed that the mean muscular strain was 5.2-19.8% MVC, the strain in the lateral neck being the highest. Peak muscular strain (over 50% MVC) occurred almost only during the encounters and usually in the lateral neck. Other muscles were subjected to fewer peak strain episodes; most of these occurred in the back. At least one peak strain episode exceeding 100% MVC was recorded for every muscle studied. The highest peak strain 257% MVC, was measured in the lateral neck. This peak strain episode caused an injury to the lateral neck area, and the flight mission was discontinued. CONCLUSIONS: The mean muscular strain measured in this study was rather low. However, the strain occurring in the lateral neck and the back exceeds the ergonomic recommendations for static work. Especially in the lateral neck, and to some extent in the back, peak strain occurs frequently, in a magnitude that is well above the maximal voluntary contraction; in these areas, the peak strain presents a potential risk of injury and negative health effects. The level and frequent occurrence of peak strain episodes means that fighter pilots' muscular strength and muscular endurance, especially in the neck and shoulder area, are subjected to demands clearly higher than those of the average population.

Muscle fatigue caused by repeated aerial combat maneuvering exercises.

BACKGROUND: Little is known about the development of in-flight muscular fatigue during repeated flights. HYPOTHESIS: This study was conducted to evaluate muscular fatigue in different upper body and neck muscles during repeated aerial combat maneuvering exercises. METHODS: Six pilots volunteered as test subjects. They performed one-to-one dog fight exercise three times (1 pilot, four times) in one day. During the flights, the pilots' electromyographic activity (EMG) was measured from the abdomen, back, neck and lateral neck. The mean muscular strain for each muscle was calculated. Before the first flight and after each flight, the maximal isometric strength of each muscle was measured. RESULTS: The results showed that maximal isometric strength between the first and last measurement decreased in the back, neck (p < 0.05) and lateral neck muscles. While the G-stress remained the same, the muscular strain during exercises increased in every muscle, but was significant only in neck and lateral neck (p < 0.05-0.01). Due to these changes, the fatigue index in the neck and lateral neck muscles was 2.0-2.1, and 1.3-1.4 (1.0 = no fatigue) in the abdomen and back muscles. CONCLUSIONS: Repeated aerial combat maneuvering exercises caused fatigue in every muscle studied. The fatigue was greater in the neck area, which may increase the risk for neck injuries, and may reduce mission effectiveness. The fighter pilots' muscular strength and endurance in the neck area are subjected to very high demands, especially if exercises are repeated several times. The recovery of the neck muscles from fatigue after repetitive exercises should receive special attention.

Stretch- and H-reflexes of the lower leg during whole body cooling and local warming.

BACKGROUND: This study was undertaken to evaluate if possible changes in stretch- and H-reflexes could be related to the changes in the EMG activity of the cooled lower leg muscles observed during a stretch-shortening cycle exercise. METHODS: Eight subjects wearing shorts and jogging shoes were exposed once to 27 degrees C and twice to 10 degrees C for 60 min each. During the second exposure to 10 degrees C, the subject's lower legs were kept warm (10 degrees Clw) with electrical pillows. After the exposures Achilles tendon reflex (stretch reflex) was induced and the EMG activity of the triceps surae was measured. Immediately after reflex measurements the EMG activity of the triceps surae and tibialis anterior during a drop-jump (stretch-shortening cycle) was measured. After similar thermal exposures electrically induced H-reflex from the calf was measured. RESULTS: During the preactivity and stretch phases the EMG activity of the triceps surae increased after the exposure to 10 degrees C, whereas during the shortening phase it decreased. During the shortening phase cooling, on the contrary, increased the activity of tibialis surae anterior. These changes disappeared at 10 degrees Clw. At 10 degrees C the maximum EMG-amplitude of triceps surae during stretch reflex decreased (p<0.05), reflecting suppressed muscle spindle activity. Suppressed spindle activity causes the agonist to be unfacilitated and the antagonist muscle contraction to be uninhibited, which was seen in the present study as decreased agonist and increased antagonist EMG activity during the shortening phase at 10 degrees C. The Hmax/Mmax-ratio, H-reflex latency and amplitude increased at 10 degrees C (p<0.05), reflecting increased motoneuron pool excitability. This in part may explain the increased EMG activity during the preactivity and stretch phases. CONCLUSION: Cooling-induced increase in the excitability of the motoneuron pool and suppression of muscle spindle activity seem to be responsible of the EMG activity changes during the stretch-shortening cycle, consequently decreasing muscular performance.

Effects of long-term whole-body cold exposures on plasma concentrations of ACTH, beta-endorphin, cortisol, catecholamines and cytokines in healthy females.

OBJECTIVE: Cold therapy is used to relieve pain and inflammatory symptoms. The present study was designed to determine the influence of long-term regular exposure to acute cold temperature. Two types of exposure were studied: winter swimming in ice-cold water and whole-body cryotherapy. The outcome was investigated on humoral factors that may account for pain alleviation related to the exposures. MATERIAL AND METHODS: During the course of 12 weeks, 3 times a week, a group of healthy females (n = 10) was exposed to winter swimming (water 0-2 degrees C) for 20 s and another group (n = 10) to whole-body cryotherapy (air -110 degrees C) for 2 min in a special chamber. Blood specimens were drawn in weeks 1, 2, 4, 8 and 12, on a day when no cold exposure occurred (control specimens) and on a day of cold exposures (cold specimens) before the exposures (0 min), and thereafter at 5 and 35 min. RESULTS: Plasma ACTH and cortisol in weeks 4-12 on time-points 35 min were significantly lower than in week 1, probably due to habituation, suggesting that neither winter swimming nor whole-body cryotherapy stimulated the pituitary-adrenal cortex axis. Plasma epinephrine was unchanged during both experiments, but norepinephrine showed significant 2-fold to 3-fold increases each time for 12 weeks after both cold exposures. Plasma IL-1-beta, IL-6 or TNF alpha did not show any changes after cold exposure. CONCLUSIONS: The main finding was the sustained cold-induced stimulation of norepinephrine, which was remarkably similar between exposures. The frequent increase in norepinephrine might have a role in pain alleviation in whole-body cryotherapy and winter swimming.

Cardiorespiratory fitness of finnish adolescents.

We evaluated the accuracy of a submaximal cycle ergometer test to assess cardiorespiratory fitness in adolescents and provided population-based reference values. In a health study of the Northern Finland birth cohort born in 1985 - 1986 (NFBC 1986), cardiorespiratory fitness of 5375 males and females aged 15 to 16 years was measured by a submaximal cycle ergometer test by using a two-stage exercise protocol designed for this survey. A total of 4903 subjects performed two work stages. Maximal workload and peak oxygen consumption were calculated on the basis of heart rate responses by the WHO extrapolation method. An additional 472 subjects were able to finish only one work stage. For them, peak oxygen uptake was calculated by the Astrand nomogram. To evaluate the accuracy of submaximal testing, a validation sample of 90 subjects carried out both a submaximal test and a maximal cycle ergometer test with direct measurement of peak oxygen uptake. The WHO method proved to estimate peak oxygen uptake with reasonable accuracy. The Astrand nomogram method overestimated peak oxygen uptake considerably, and therefore a new single-stage regression method was applied to calculate maximal workload and peak oxygen consumption. Reference values of cardiorespiratory fitness were provided for 2690 males and 2685 females aged 15 to 16 years.

Acute and long-term effects of winter swimming and whole-body cryotherapy on plasma antioxidative capacity in healthy women.

The effects of severe cold stress on total peroxyl radical trapping antioxidant capacity of plasma (TRAP) were studied in two groups of healthy women: a whole-body cryotherapy group (WBC, n = 10) and a winter swimming group (WS, n = 10). The biovariability of TRAP values was also analysed. The WBC group was exposed to -110 degrees C for 2 min, whereas the exposure for the WS group lasted 20 s in ice-cold water. Sessions were organized three times per week for 12 weeks. Blood specimens were collected at 2, 4, 8 and 12 weeks at rest, 2 and 35 min after the cold exposures and at the corresponding times without cold exposure on a separate day. Conventional methods were used to determine TRAP values. The between-subject variation was 13.6% and the within-subject variation 6.4%. The index of individuality was 0.46, and the index of heterogeneity was 0.079. These results indicate a marked heterogeneity among subjects. During the first 4 weeks, the mean TRAP value significantly increased at 2 min after cold exposure in the WBC group, returning to baseline 35 min after the exposure. Similar changes were observed in the WS group. However, all changes due to cold were relatively mild (<5%). After 4 weeks no changes in TRAP values after the cold exposures were noticed and no long-term changes in basal TRAP values were observed. In the main, regular WBC and WS do not seem to be harmful as far as plasma antioxidative capacity is concerned.

Dynamic work in cold.

The capability of the human organism to work or exercise comprises of several components of physical performance capacity: endurance, power, force production, velocity, flexibility and co-ordination. Working in cold environments where it is possible that the temperature of the body, either superficial or core, decrease, the above mentioned components may be altered. In general, cooling decreases the ability of these components to function. The amount of decrease is dependent for example on: exercise type, exercise duration and degree of cooling. The exercises that seem to be most susceptible to cooling are those which are very short lasting and dynamic, utilising fast movement velocities and/or elastic properties of the working muscles. The decrease in core temperature, however is not a prerequisite for the decrease in performance. Already a very superficial cooling is sufficient to substantially decrease performance. Several mechanisms may be responsible for the decreased capacity of performance and they can severely suffocate the capacity to work in cold environments. Due to this an increase in individual strain and also the risk to have an accident are increased. Therefore, while working in cold environments cooling, especially of the working muscles, has to be avoided as efficiently as possible.

Physical characteristics and decrement in muscular performance after whole body cooling.

The dependence of cooling-induced decrement in muscular performance on several physical characteristics was studied. The characteristics were: the amount of subcutaneous fat, body weight, height and surface area, maximal aerobic capacity and maximal voluntary isometric contraction of the trunk flexors. Ten male subjects wearing shorts and jogging shoes were exposed to 27 degrees C and 10 degrees C for 60 min. The cooling resulted in a decrease of 6.8 +/- 0.3 degrees C (mean +/- SE) in mean skin temperature. The temperatures of m. triceps and m. deltoideus were decreased by 2.8 +/- 1.0 degree C and 5.1 +/- 0.4 degree C, respectively. Rectal temperature was virtually unaffected. A significant negative correlation (r = -0.785) was found between the amount of subcutaneous fat and decrease in mean skin temperature after cooling. After the exposures to 27 degrees C and 10 degrees C, the subjects performed an overhead ball throwing test to measure muscular performance. The test was performed in a standing position using both arms. Five balls weighing from 0.27 kg to 3.0kg were thrown. On the average, cooling decreased muscular performance 7.6%. The decrease correlated significantly only with the amount of subcutaneous fat r = -0.710). The results indicate that from the measured physical characteristics, varying within normal range, only subcutaneous fat had significant effect on thermal responses. Accordingly, the decrease in muscular performance correlated only with the amount of subcutaneous fat.

Muscle performance and electromyogram activity of the lower leg muscles with different levels of cold exposure.

The purpose of this study was to evaluate the relationship between different levels of body cooling and muscle performance decrement and to study the motor co-ordination of the working agonist-antagonist muscle pair of the lower leg. Eight volunteer male subjects dropped from a 40-cm bench on to a force plate and performed a maximal rebound jump (stretch-shortening cycle). The jumps were performed after 60-min exposures to 27 degrees C, 20 degrees C, 15 degrees C and 10 degrees C. In comparison to those at 27 degrees C, all the exposures to lower temperatures decreased the flight time of the jump, average force production and take-off velocity in a dose-dependent manner. The changes in electromyogram (EMG) activity also behaved in a dose-dependent manner. During pre-activity and stretch phases the integrated EMG (iEMG) activity of the agonist muscle (triceps surae) increased due to cooling (at 10 degrees C, P < 0.05). In contrast, during the shortening phase iEMG of the agonist muscle decreased due to cooling (at 15 degrees C and 10 degrees C, P < 0.05). Moreover, the activity of the antagonist muscle (tibialis anterior) increased due to cooling (at 15 degrees C and 10 degrees C, P < 0.01). The mean power frequency of the agonist muscle during the shortening phase was shifted from 124 (SEM 12) Hz (at 27 degrees C) to 82 (SEM 7) Hz (at 10 degrees C, P < 0.01). We concluded that there was a dose-dependent response between the degree of cooling and the amount of decrease in muscle performance as well as EMG activity changes. A relatively low level of cooling was sufficient to decrease muscle performance significantly.

Cardiorespiratory strain of a five day jogging relay.

The heart rates of 14 voluntary subjects (seven male and seven females) participating in a 5 d jogging relay were recorded. The jogging speed was controlled at 3.0 m.s-1 on average. The heart rate measurements were related to cardiorespiratory responses obtained during VO2max test on a treadmill. The mean (s.d.) VO2max values were 53(2) and 48(2) ml.kg-1.min-1 and the anaerobic threshold was 42(1) and 38(2) ml.kg-1.min-1 for male and female subjects respectively. During the relay the mean(s.d) heart rate values of male and female subjects were 150(1), and 167(3) beats.min-1 (P < 0.001), corresponding to 68(1) and 76(2)% VO2max (P < 0.01) as calculated from the individual HR/VO2 regression equations. The jogging time above anaerobic threshold heart rate level was 9(3)% for the males and 43(7)% for the females (P < 0.001) of the total jogging time. The results indicate that even in a leisure oriented jogging event, cardiorespiratory strain can be rather high and that the strain can be significantly higher for female than for male subjects. The determination of the anaerobic threshold as well as VO2max is important when quantifying the level of cardiorespiratory strain of exercise.

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

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

Rewarming of feet by lower and upper body exercise.

The capacity of different types of exercise to rewarm the body, especially the feet, was studied. Six healthy male subjects wearing winter clothing (2.4 clo, 0.37 degrees C.m2.W-1) were exposed on three occasions to -15 degrees C for 120 min. For the first 60 min the subjects were cooled while sitting motionless and for the latter 60 min they were submitted to cycle ergometer exercise (CE), arm ergometer exercise (AE) or step exercise (ST). The rate of work in CE (about 350 W) served as a reference value for AE and ST. The cooling resulted in an average 1.7 (SEM 0.03) degrees C decrease in mean body temperature (Tb) corresponding to a 425 (SEM 9) kJ heat debt. The ST increased most effectively mean skin, rectal and lower body skin temperatures as well as dry heat loss. The ST increased Tb by 0.83 (SEM 0.16) degrees C, CE by 0.10 (SEM 0.11) degrees C and AE by only 0.07 (SEM 0.12) degrees C. At the end of the exercise the foot temperature was approximately 6 degrees C higher in ST than in CE. The superior rewarming by ST was apparently due to its low mechanical efficiency. Because the increase in Tb could not explain all the changes in foot temperatures, increased circulation and metabolism of the feet would also appear to have been involved.

Water balance and physical performance in cold.

Although a lot of attention is focused on problems of energy balance and nutrition in cold environment, water balance has received less attention. In a cold environment the water balance might be disturbed because the need of water could be increased, the use of water could be decreased and the redistribution of blood could change water volume in circulation. In dehydrated subjects, exercising at -15 degrees C at submaximal work level, both oxygen uptake and heart rate were significantly higher during water deprivation while the anaerobic threshold was lower. The time before reaching exhaustion was also shortened. However, maximal oxygen uptake and maximal muscle strength were not affected. The results suggest lower efficiency, higher physical strain and earlier exhaustion of dehydrated subjects in cold. After repletion of 1.8% body weight loss by an equal amount of fluid (5% sucrose solution) the oxygen uptake was significantly decreased at a submaximal work level at -20 degrees C, suggesting an improved mechanical efficiency and decreased physical strain. Although physical performance could be restored by rehydration, a rapid rehydration is not recommended because of increased diuresis, increased blood pressure and vigorous shivering stimulated by cold fluids. Instead, a continuous maintenance of water balance is recommended, with a fluid temperature above 25-30 degrees C and with a carbohydrate content below 7%.

Effects of leg covering in humans on muscle activity and thermal responses in a cool environment.

Thermal responses and muscle performance in humans were studied during rest and exercise in a cool environment with different clothing distributions over the legs. Nine female subjects were exposed to 5 degrees C wearing shorts (SS), trousers with long legs (LL) or trousers with one long leg and one short leg (LS: LSc covered leg, LSu uncovered leg). The subjects also wore T-shirts and long-sleeved shirts. The subjects were seated for 60 min and after this they performed light stepping exercise for a further 60 min. Rectal temperature (T(re)) and skin temperature from seven (LL, SS) or nine sites (LS) were measured continuously. Surface electromyography (EMG) from three muscles (biceps femoris, gastrocnemius and tibialis anterior) were recorded during the exercise from six subjects. Integrated EMG (iEMG) and mean power frequency (MPF) were used to describe muscle activity. The T(re) was virtually unchanged during rest in every ensemble, whereas during exercise T(re) was significantly lower in SS than in LL. Mean skin temperature (T(sk)) decreased during rest in every ensemble, being significantly lower in SS than in LL. After the rest period local T(sk) of thigh and calf were significantly lower in SS than in LL and they were also lower in LSu than in LSc. At the beginning of the exercise the iEMG of the tibialis anterior muscle in SS and LL averaged 84 (SEM 7) and 64 (SEM 3) mu V (P <0.05), respectively. Respective values for LSu and LSc were 86 (SEM 9) and 66 (SEM 6) mu V (P <0.05). The MPF of the tibialis anterior muscle was significantly higher in LL 102 (SEM 5) Hz than in SS 90 (SEM 5) Hz (P <0.05) and similarly the MPF of the gastrocnemius muscle was also higher in LL 111 (SEM 5) Hz than in SS 100 (SEM 5) Hz (P < 0.05). It was concluded that exposing bare legs to a cool environment enhanced the motor unit activity in relation to covered legs. This would suggest that wearing shorts in a cool environment may, at the beginning of exercise, result in higher (about 25 percent) EMG activity and this may reflect increased muscle strain in comparison with wearing long trousers. Our results showing a unilateral increase in EMG activity during unilateral cooling suggest that the increase of strain is restricted to the uncovered part of the limb.

Responses to whole body and finger cooling before and after an Antarctic expedition.

Eight subjects, who were indoor workers and not habitually exposed to cold, spent 53 days in Antarctica. They did mainly geological field work often requiring the use of bare hands. The effects of the expedition on responses to a whole body cold exposure test, a finger blood flow test and a cold pressor test were studied. After the expedition, during whole-body cooling the time for the onset of shivering was delayed by 36 min (P < 0.001) and forearm and thigh temperatures were 1.5 degrees C higher (P < 0.05) at the end of exposure. During local cooling of the finger with 10 degrees C perfusion, finger vascular resistance was 14.9 (SEM 6.6) mmHg.ml-1.min.100 ml (P < 0.05) lower and finger temperature 3.9 (SEM 0.8) degrees C higher (P < 0.01). However, the decrease in rectal temperature during whole-body cooling was unaltered and the response to a cold pressor test was unchanged. The data would indicate that partial acclimatization to cold had been developed. Changes in forearm temperature were correlated with the duration of cold exposure of the hands (P < 0.05) and finger vascular resistance and finger temperature were correlated with responses to cooling before the expedition (P < 0.001 and P < 0.01, respectively). Because the ambient temperature was not clearly lower in Antarctica in comparison to Finland, the reason for the changes developed seems to be the increased exposure to the outdoor climate in Antarctica.

Influence of cold shivering on fine motor control in the upper limb.

The aim of the investigation was to determine the effects of cold shivering on the accuracy of force output in distal, middle and proximal muscles of the upper limb. Test of hand grip strength, elbow flexion and shoulder flexion (each done at 10% maximal voluntary contraction for 15 s) were done under three conditions: (1) thermoneutral air (27 degrees C), a condition of thermal comfort; (2) cold air (10 degrees C), a condition eliciting an increase in tonic muscle activity; (3) and cold air (10 degrees C) with a cold drink (8 degrees C), a condition that causes visible shivering. The averaged (root mean square) electromyogram (AEMG) and mean power frequency (MPF) were measured from proximal, middle and distal arm muscles during the tests and compared. The control of force output was highly effective at thermoneutral condition for all motor tasks. During the cold air condition, all muscles were tonically active but there was no effect on accuracy of test performance. However, AEMG increased approximately 20% (P < 0.05) with respect to test performance in thermoneutral condition. During the cold air/cold drink condition, all muscles were shivering to a different extend. AEMG during test performance increased 30-150% in comparison to thermoneutral condition (P < 0.05). In this case, hand grip and elbow flexion were not adversely affected (these tests require middle and distal muscles) by cold shivering. However, the accuracy of performance of shoulder flexion was adversely affected. This is consistent with the fact that proximal muscles are more active during cold shivering.