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Physical performance and somatic, psychological and flu-like symptoms before and after 8 days of military field training
Abstract
Book of Abstracts: p. 188
... Most commonly, the researchers have focused on changes occurring from the psychological aspects [2][3][4][5][6]. Less explored in survival literature are studies focused on changes in coordinations motor skills and physical fitness during survival training [7][8][9][10][11]. ...
... The effect of 36 hours of moderate physical activity combined with sleep deprivation on body balance disturbation tolerance skills (BBDTS) was determined using the rotation test [8,11]. In the presented study, there was deterioration of BBDTS duration the survival training. ...
... The tests conducted revealed that with prolonged time of exercise, the cadets deteriorated in performing tasks requiring the effort of large muscle groups (running motor adjustment, -----rotational test and arm muscles strength), whereas tasks involving precise actions (psychomotor performance, forearm muscles force differentiation and shooting) were not affected, or even improved slightly. Air force cadets performed the running test with a similar score throughout the whole 36-hour experiment, whereas pilots, 15 years older, obtained a lower score at the end of training of the same duration [11]. Soldiers from the special unit presented such a deterioration in performance only at the end of 72-hour survival training [15]. ...
Introduction: Preparation of air force cadets to survive in isolation is a necessary element of their training, demonstrating how hard conditions they can encounter in combat necessity. The aim of the study was to examine the influence of 36 hours long field survival conditions combined with sleep deprivation on selected motor coordination and psychomotor indices.
Methods: Fifteen air force cadets aged 19.6±0.3 years exercised for 36 hours during survival training without a possibility to sleep. They were examined four times (Day 1 – before effort, Day 2 – after 24 hours of training, Day 3 – directly after 36 hours of training, Day 4 – next day, after the all night rest) for shooting and psychomotor performance, motion coordination, running motor adjustment, handgrip force differentiation and on Day 1 and 3 exercise capacity was evaluated with 1 mile walking test.
Results: Survival training resulted in significant decreases in maximum handgrip strength, corrected 50% max handgrip, dynamic balance and heart rate. No changes occurred in psychomotor indices, running motor adjustment and shooting performance. Overnight rest did not result in recovery of any of the examined factors to the values observed on Day 1.
Conclusion: Survival training combined with sleep deprivation mostly affected peripheral factors depending on strong action from both muscles and nervous system, whereas complex tasks involving short term central alertness and moderate exertion were maintained. In order to improve performance more endurance strength training, if possible combined with sleep deprivation, should be introduced in military training.
... The analysis of the described real-life actions of soldiers in isolation revealed that these changes may last from several hours to several days [15]. The influence of prolonged military training on psychomotor performance, balance, motor accommodation and the ability to differentiate forearm muscle strength was studied [16,17,18,19,20,21,22]. It may be presumed that fatigue resulting from sleep deprivation will cause an increase in muscle tone and, consequently, increased physiological tremor amplitude [23,24] and possibly shift in frequencies of power spectral density (PSD) maxima. ...
... Post-hoc comparisons revealed (Figure 7) that the difference concerning mean values of the index evaluating tremor power in low frequencies L 2-4 at measurement 0 and measurement 3 differed significantly (p<0.01). No significant differences were found in mean values of index L [10][11][12][13][14][15][16][17][18][19][20] ...
... The first denoted the mean logarithm of the low-frequency components' power of the analysed signal (2 -4 Hz). The latter referred to high-frequency components(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Each index was calculated from the following formula: ...
The aim of the study was to define the changes of the characteristics of physiological postural tremor under conditions of increasing fatigue and lack of sleep during prolonged military training (survival). The subjects of the study were 15 students of the Polish Air Force Academy in Dęblin. The average age was 19.9±1.3 years. During the 36-hour-long continuous military training (survival) the subjects were deprived of sleep. Four tremor measurements were carried out for each of the subjects: Day 1 - morning, after rest (measurement 0); Day 2 - morning, after overnight physical exercise (measurement 1); afternoon, after continuous sleep deprivation (measurement 2); Day 3 - morning, after a full night sleep (measurement 3). The accelerometric method using an acceleration measuring kit was applied to analyse tremor. A significant difference between mean values of the index evaluating tremor power in low frequencies L2-4 in measurement 0 and measurement 3 was observed (p<0.01). No significant differences were found in mean values of index L10-20. Mean frequencies F2-4 differed significantly from each other (F2,42=4.53; p<0.01). Their values were 2.94±0.11, 2.99±0.9, 2.93±0.07 and 2.91±0.07 for successive measurements. A gradual, significant decrease of F8-14 was observed (F2,42=5.143; p<0.01). Prolonged sleep deprivation combined with performing tasks demanding constant physical effort causes long-lasting (over 24 hours) changes of the amplitude of low-frequency tremor changes. This phenomenon may significantly influence psychomotor performance, deteriorating the ability to perform tasks requiring movement precision.
Body-weight management requires a multifactorial approach. Recent findings suggest that an elevated protein intake seems to play a key role herein, through (i) increased satiety related to increased diet-induced thermogenesis; (ii) its effect on thermogenesis; (iii) body composition; and (iv) decreased energy-efficiency, all of which are related to protein metabolism. Supported by these mechanisms, relatively larger weight loss and subsequent stronger body-weight maintenance have been observed. Increased insulin sensitivity may appear, but it is unclear whether this is due to weight loss or type of diet. The phenomenon of increased satiety is utilized in reduced energy-intake diets, mainly in the ad libitum condition, whereby sustained satiety is achieved with sustained absolute protein intake in grams, despite lower energy intake. Elevated thermogenesis and glucagon-like peptide-1 (GLP-1) appear to play a role in high-protein induced satiety. Under conditions of weight maintenance, a high-protein diet shows a reduced energy efficiency related to the body composition of the body weight regained, that is, in favor of fat-free mass. Indeed, during body-weight loss, as well as during weight regain, a high-protein diet preserves or increases fat-free mass and reduces fat mass and improves the metabolic profile. In the short-term this may be supported by a positive protein and a negative fat balance, through increased fat oxidation. As protein intake is studied under various states of energy balance, absolute and relative protein intake needs to be discriminated. In absolute grams, a normal protein diet becomes a relatively high-protein diet in negative energy balance and at weight maintenance. Therefore, 'high protein negative energy balance diets' aim to keep the grams of proteins ingested at the same level as consumed at energy balance, despite lower energy intakes.
The aim of this work was to investigate the effect of a daily mixed nutritional supplement upon body composition, physical performance, and circulating anabolic hormones in soldiers undergoing arduous training. Thirty males received either a habitual diet alone (CON, n = 15) or with the addition of a daily mixed supplement (SUP, n = 15) of ∼5.1 MJ·d–1 during 8 weeks of training. Body composition (DEXA), maximal dynamic lift strength (MDLS), and vertical jump (VJ) were assessed, and resting blood samples were collected before and after training. Blood analysis included insulin-like growth factors (IGF-1, IGF BP-1, and IGF BP-3), testosterone, and cortisol. There were no group differences at baseline. Body mass loss (mean ± SD) (CON 5.0 ± 2.3, SUP 1.6 ± 1.5 kg), lean mass loss (CON 2.0 ± 1.5, SUP 0.7 ± 1.5 kg), and fat mass loss (CON 3.0 ± 1.6, SUP 0.9 ± 1.8 kg) were significantly blunted by SUP. CON experienced significant decrements in MDLS (14%), VJ (10%), and explosive leg power (11%) that were prevented by SUP. Military training significantly reduced circulating IGF-1 (28%), testosterone (19%), and the testosterone:cortisol ratio (24%) with no effect of SUP. Circulating IGF BP-1 concentration and cortisol remained unchanged throughout, although SUP abolished the significant decrease in circulating IGF BP-3 (20%) on CON. In conclusion, a daily mixed nutritional supplement attenuated decreases in body mass and lean mass and prevented the decrease in physical performance during an arduous military training program.
We determined the effects of varying daily carbohydrate intake by providing or withholding carbohydrate during daily training on endurance performance, whole body rates of substrate oxidation, and selected mitochondrial enzymes. Sixteen endurance-trained cyclists or triathletes were pair matched and randomly allocated to either a high-carbohydrate group (High group; n = 8) or an energy-matched low-carbohydrate group (Low group; n = 8) for 28 days. Immediately before study commencement and during the final 5 days, subjects undertook a 5-day test block in which they completed an exercise trial consisting of a 100 min of steady-state cycling (100SS) followed by a 7-kJ/kg time trial on two occasions separated by 72 h. In a counterbalanced design, subjects consumed either water (water trial) or a 10% glucose solution (glucose trial) throughout the exercise trial. A muscle biopsy was taken from the vastus lateralis muscle on day 1 of the first test block, and rates of substrate oxidation were determined throughout 100SS. Training induced a marked increase in maximal citrate synthase activity after the intervention in the High group (27 vs. 34 micromol x g(-1) x min(-1), P < 0.001). Tracer-derived estimates of exogenous glucose oxidation during 100SS in the glucose trial increased from 54.6 to 63.6 g (P < 0.01) in the High group with no change in the Low group. Cycling performance improved by approximately 6% after training. We conclude that altering total daily carbohydrate intake by providing or withholding carbohydrate during daily training in trained athletes results in differences in selected metabolic adaptations to exercise, including the oxidation of exogenous carbohydrate. However, these metabolic changes do not alter the training-induced magnitude of increase in exercise performance.
Prolonged, exhaustive exercise frequently leads to an increased incidence of upper respiratory tract illness (URTI) which is linked to transient immunodepression. We investigated potential biochemical markers of stress and fatigue, and URTI symptoms as a surrogate of immunodepression, in US Marines undergoing intensive winter training at altitude. Selected plasma amino acids and leptin (p[Lep]) were measured as possible markers of fatigue and immunodepression, together with nonesterified fatty acids (p[NEFA]) and total antioxidant capacity (p[TAC]). Changes were observed in plasma free tryptophan (p[FT]), p[Gln], p[Lep], p[NEFA], p[TAC] but not branched chain amino acids (p[BCAA]). p[FT] decreased markedly. Resting p[Gln] decreased overall after one month at altitude. p[Gln] routinely decreases 1-2 hrs after prolonged exercise. Importantly, we observed early morning decreases in p[Gln], suggesting a cumulative effect of prolonged activity, stress, and fatigue. Concomitantly, individuals with highest illness scores had the greatest p[Gln] decrease: low p[Gln] may therefore be associated with a diminished stress tolerance.
To examine the influence of dietary protein on lean body mass loss and performance during short-term hypoenergetic weight loss in athletes.
In a parallel design, 20 young healthy resistance-trained athletes were examined for energy expenditure for 1 wk and fed a mixed diet (15% protein, 100% energy) in the second week followed by a hypoenergetic diet (60% of the habitual energy intake), containing either 15% (approximately 1.0 g x kg(-1)) protein (control group, n = 10; CP) or 35% (approximately 2.3 g x kg(-1)) protein (high-protein group, n = 10; HP) for 2 wk. Subjects continued their habitual training throughout the study. Total, lean body, and fat mass, performance (squat jump, maximal isometric leg extension, one-repetition maximum (1RM) bench press, muscle endurance bench press, and 30-s Wingate test) and fasting blood samples (glucose, nonesterified fatty acids (NEFA), glycerol, urea, cortisol, free testosterone, free Insulin-like growth factor-1 (IGF-1), and growth hormone), and psychologic measures were examined at the end of each of the 4 wk.
Total (-3.0 +/- 0.4 and -1.5 +/- 0.3 kg for the CP and HP, respectively, P = 0.036) and lean body mass loss (-1.6 +/- 0.3 and -0.3 +/- 0.3 kg, P = 0.006) were significantly larger in the CP compared with those in the HP. Fat loss, performance, and most blood parameters were not influenced by the diet. Urea was higher in HP, and NEFA and urea showed a group x time interaction. Fatigue ratings and "worse than normal" scores on the Daily Analysis of Life Demands for Athletes were higher in HP.
These results indicate that approximately 2.3 g x kg(-1) or approximately 35% protein was significantly superior to approximately 1.0 g x kg(-1) or approximately 15% energy protein for maintenance of lean body mass in young healthy athletes during short-term hypoenergetic weight loss.
Anecdotal information and limited research suggest that short-term caloric deprivation adversely affects cognition. However, this issue has not been studied using double-blind, placebo-controlled procedures, because the formulation of a calorie-deficient feeding regimen identical to one with calories is impossible using ordinary foods. Therefore, test meals varying in caloric content, but indistinguishable in sensory characteristics, were formulated using hydrocolloid-based gels as the principal structural component.
The purpose of this study was to examine the effects of 2 d of near-total caloric deprivation on cognitive function, satiety, activity, sleep, and glucose concentrations in a controlled environment.
A double-blind, placebo-controlled crossover study of caloric deprivation was conduced in a controlled environment for 48 h. Cognitive function in 27 healthy young subjects was assessed repeatedly with standardized tests of vigilance, reaction time, learning, memory, logical reasoning, mood, and satiety. Wrist-worn monitors were used to assess ambulatory vigilance, activity, and sleep. Interstitial glucose concentrations were assessed continuously with a minimally invasive monitor.
When the subjects received the near calorie-free diets, mean calorie consumption totaled 1311 kJ (313 kcal) over the testing period. During the fully fed treatment sessions, the subjects consumed a mean of 9612 kJ/d (2294 kcal/d), which matched their individual, daily energy requirements. Satiety and interstitial glucose concentrations were lower during the calorie-deprived diet (P < 0.001) than during the fully fed diet. There were no detectable effects of calorie deprivation on any aspect of cognitive performance, ambulatory vigilance, activity, or sleep. The mood states assessed, including fatigue, were not affected by calorie deprivation.
Cognitive performance, activity, sleep, and mood are not adversely affected in healthy humans by 2 d of calorie-deprivation when the subjects and investigators are unaware of the calorie content of the treatments.
In an effort to determine whether or not field living conditions degrade performance during cold weather military training, performance of 17 Norwegian Army soldiers living in tents in the field (FG) was compared with that of 13 soldiers living in barracks (GG). FG and GG performed similar tasks and were equipped and clothed identically. Each subject was tested prior to and following 9 days of field training. The tests consisted of marksmanship (score for a 5-shot group), snowshoe running (time to cover 1700 m), anaerobic power (Wingate test), and performance on 5 cognitive tests (preferred hand tapping, 4-choice reaction time, pattern recognition, memory search, and code substitution; each test scored as % correct and # completed). A subset of the subjects from each group wore watches which recorded heart rate during the day. During training GG had a lower average heart rate than FG, indicating lower physical activity level. Significant changes were not found in rifle shooting or in mean anaerobic power. Significant group (p less than .001) and time (p less than .001; pre vs. post) differences were found in snowshoe time, but a significant interaction was not found. Among the cognitive tests, a significant group by time interaction was found for % correct responses only for the Memory Search task, and represented a decrease in GG performance while FG performance was maintained. Time differences were found for # completed for Memory Search (p less than .002) and Pattern Recognition (p less than .001) suggesting incomplete learning of the task, but no group by time interactions were found.(ABSTRACT TRUNCATED AT 250 WORDS)
Deuterium or tritium labeled water traditionally has been used for the measurement of total body water by application of the dilution principle. However, these methods have not enjoyed wide clinical use. The use of deuterium is hampered by the tedious and time consuming nature of the analysis while the use of tritium involves a radiation hazard. In addition, exchange of the label with nonaqueous hydrogen in the body raises questions about the accuracy of total body water values. To determine if water labeled with the stable isotope 18O can yield faster and more accurate results, total body water was measured simultaneously using water labeled with both 18O and 2H. The 18O and 3H dilutions were measured by mass spectrometry. The relative precision of the body water value using the 18O method was 2% for both serum and breath analysis. The 18O was fully equilibrated within 2 to 3 hr after administration, and results from the analysis of breath CO2 could be readily obtained within 1 hr after sampling. The H2(18)O dilution space averaged 3.0% (SE = 0.4) less than the 2HHO dilution space, because the latter exchanges with nonaqueous hydrogen. For this reason, the H2(18)O dilution should be a more accurate measure of total body water than the 3HHO dilution.
Isometric maximal handgrip strength (GSmax) has been used as an expedient test of overall muscle strength and index of fat-free mass (FFM). We tested this relationship in 55 fit young men undergoing high rates of FFM loss in an 8.5-wk military training course involving multiple stressors including nutritionally uncomplicated energy deficit. GSmax was measured by a hand dynamometer interfaced with a computer providing visual feedback; another strength test, measuring dynamic strength of larger muscle groups (Cleansim), was also performed. GSmax did not change (530 +/- 57 vs 529 +/- 63 N) in the face of a 15.6% loss of body weight (12.1 +/- 3.4 (SD) kg), including 6.9% loss of FFM (4.6 +/- 2.6 kg), but Cleansim decremented significantly (77.4 +/- 9.6 to 58.7 +/- 8.9 kg) and changes were significantly correlated with delta FFM for GSmax (r = 0.31) and Cleansim (r = 0.49). We conclude that GSmax is not a good representation of changes in total FFM in healthy young men even though it appears to be useful in more severely catabolic patients with extreme losses of FFM and in pubertal boys making large gains in FFM. Other aspects of physical performance are clearly affected by high rates of weight loss, as demonstrated by decrements in the Cleansim and its stronger relationship to delta FFM.
Previous studies have demonstrated that full recovery from weight loss may take months or years. The present investigation examined short-term recovery (5 wks "post") of physical performance (muscular strength, muscular power, vertical jump), body composition, metabolic hormones (testosterone, luteinizing hormone, sex hormone binding globulin, insulin-like growth factor-1, triiodothyronine, thyroxine, thyroid binding globulin, and thyroid-stimulating hormone) and metabolic markers (transferrin, ferritin, prealbumin, glycerol, nonesterified fatty acids, high-density lipoproteins, and lactate) in 10 healthy young men after an 8-week Army course with an energy deficit (1000 kcal/d) and loss of body mass (-12%). Subjects ate ad libitum after the course ended ("post"). Body composition was determined by dual-energy X-ray absorptiometry; strength from a simulated power clean, power from body mass and jump height, and metabolic hormones were measured in morning-fasted blood by radioimmunoassay. With the exception of transferrin and glycerol, all study parameters were significantly (p<.05) altered by the training course. At 5 weeks post fat-free mass along with all physical performance measures returned to initial levels; however, fat mass had significantly (p<.05) increased over initial levels. Also, with the exception of lactate, all measured hormones and markers were close to initial levels and within normal ranges. Reported complications during recovery included sleep irregularities, diarrhea, loss of motivation and feelings of fatigue. While the long range effect of this energy deprivation experience is uncertain, these data do suggest that severe weight loss does not result in lasting alterations of the contractile and metabolic properties of skeletal muscle in young, lean, healthy men.
We investigated the effects of progressively increased training load and overtraining on resting and intrinsic heart rate (IHR) and cardiac autonomic modulation (CAM), and their relationships to performance variables. Nine athletes (ETG) increased training volume at 70-90% of maximal oxygen uptake (VO2max) by 130% (p<0.01) and training volume at <70% VO2max by 100% (p < 0.01) during 6-9 weeks. The corresponding increases in six female control athletes (CG) were 5 and 10%. Pharmacological blocking through atropine and propranolol and the Rosenblueth and Simeone model were used to calculate the sympathovagal balance index (Abal) and to measure IHR. The results were analysed using two-way analysis of variance. VO2max, IHR and Abal did not change. Resting heart rate had a tendency to decrease in the ETG and increase in the CG during the training period (interaction p < 0.01). Five ETG athletes demonstrated overtraining state (OA subgroup). Their VO2max (mean+/-SEM) decreased from 53.0+/-2.2 ml x kg(-1) x min(-1) to 50.2+/-2.3 ml x kg(-1) x min(-1) (p < 0.01), but no changes in resting HR, IHR and Abal were found. A significant correlation between the baseline values of VO2max and the parasympathetic activity index was found (r=-0.59, p < 0.05). In conclusion, progressively increased training load and overtraining did not induce significant changes in intrinsic heart rate or cardiac autonomic modulation in female endurance athletes. Resting heart rate rather decreased with heavy endurance training and overtraining. High maximal oxygen uptake was correlated with high cardiac parasympathetic modulation.
We tested the hypothesis that key endocrine responses to semistarvation would be attenuated by changing only the food intake in a multistressor environment that also included sustained workload, inadequate sleep, and thermal strain. Serum hormones were compared within and between two groups of healthy young male volunteers participating in the 8-wk US Army Ranger course, with four repeated cycles of restricted energy intakes and refeeding: group 1 (n = 49) and group 2 (n = 48); energy deficits averaged 1,200 and 1,000 kcal/day, respectively. After 8 wk, most of group 1 achieved a minimum body fat, serum 3,5,3'-triiodothyronine (T(3)) was below normal (78 +/- 20 ng/dl), testosterone (T) approached castrate levels (4.5 +/- 3.9 nmol/l), insulin-like growth factor I (IGF-I) declined by one-half (75 +/- 25 microg/l), and cholesterol rose from 158 +/- 31 to 217 +/- 39 mg/dl. Bioavailable T(3) and T were further reduced by increases in their specific binding proteins in response to declining insulin. Refeeding, even with continuation of the other stressors, produced prompt recovery of T(3), T, and IGF-I. Higher energy intakes in group 2 attenuated the subclinical hypothyroidism and hypercholesterolemia, whereas consistent luteinizing hormone suppression indicated centrally mediated threshold effects on gonadal hormone suppression. We conclude that low T, T(3), and IGF-I remained reliable markers of acute energy deficits in the presence of other stressors; elevated cholesterol and cortisol provided information about chronic status, corresponding to diminishing body fat stores.
Energy requirements of military personnel (Soldiers, Sailors, Airmen, and Marines) have been measured in garrison and in field training under a variety of climatic conditions. Group mean total energy expenditures for 424 male military personnel from various units engaged in diverse missions ranged from 13.0 to 29.8 MJ (3109-7131 kcal) per day. The overall mean was 19.3+/-2.7 MJ (mean+/-SD) (4610+/-650 kcal) per day measured over an average of 12.2 days (range 2.25-69 days). For the 77 female military personnel studied, mean total energy expenditures for individual experimental groups ranged from 9.8 to 23.4 MJ (2332-5597 kcal) per day, with an overall mean of 11.9+/-2.6 MJ (2850+/-620 kcal) per day, measured over an average of 8.8 days (range 2.25-14 days). Women, presumably due to their lower lean body mass, resting metabolic rate, and absolute work rates, had lower total energy expenditures. Combat training produced higher energy requirements than non-combat training or support activities. Compared to temperate conditions, total energy expenditures did not appear to be influenced by hot weather, but tended to be higher in the cold or high altitude conditions.
The present study observed the effects of a 6-day high carbohydrate (H-CHO) diet on salivary cortisol and IgA during a period of increased exercise workload. Thirty-two competitively trained male triathletes were randomly allocated into a self-selected (SS), or an H-CHO (12 g CHO kgbm (-1) . day (-1)) dietary group. In addition to their training regimes, all subjects performed a 1-hour running exercise bout at 70 % V.O (2max) . d (-1), for six days. Saliva samples were taken pre, immediately post, and morning post-exercise bout on days 1, 4, and 6. The concentrations of s-IgA and cortisol were determined by ELISA assays. There was a significant (p < 0.001) interaction between Group x Time for cortisol, with a marked increase in concentrations occurring in the SS dietary group pre to post exercise, and pre to morning post-exercise (p < 0.01). Conversely, a significant (p = 0.009) Group x Time interaction reflected higher post exercise s-IgA concentrations (p < 0.005) than pre exercise in the H-CHO diet group. Blood glucose concentration decreased pre to post exercise in the SS diet group (p < 0.01), whilst remaining stable in the H-CHO group. It is concluded that the consumption of a high CHO diet throughout a 6-day period of overtraining had a favourable effect on markers of immune activity and thereby reduced the susceptibility of these endurance athletes to upper respiratory tract infection URTI.
A simple test for the measurement of mechanical power during a vertical rebound jump series has been devised. The test consists of measuring the flight time with a digital timer (0.001 s) and counting the number of jumps performed during a certain period of time (e.g., 15–60 s). Formulae for calculation of mechanical power from the measured parameters were derived. The relationship between this mechanical power and a modification of the Wingate test (r=0.87, n=12 ) and 60 m dash (r=0.84, n=12 ) were very close. The mechanical power in a 60 s jumping test demonstrated higher values (20 WkgBW–1) than the power in a modified (60 s) Wingate test (7 WkgBW–1) and a Margaria test (14 WkgBW–1). The estimated powers demonstrated different values because both bicycle riding and the Margaria test reflect primarily chemo-mechanical conversion during muscle contraction, whereas in the jumping test elastic energy is also utilized. Therefore the new jumping test seems suitable to evaluate the power output of leg extensor muscles during natural motion. Because of its high reproducibility (r=0.95) and simplicity, the test is suitable for laboratory and field conditions.
HAWLEY, J.A. and L. M. BURKE. Carbohydrate availability and training adaptation: effects on cell metabolism. Exerc. Sport Sci. Rev., Vol. 38, No. 4, pp. 152Y160, 2010. Several markers of endurance training adaptation are enhanced to a greater extent when individuals undertake selected training sessions with low compared with normal muscle glycogen content or with low exogenous carbohydrate availability. The potential mechanisms underlying the cellular responses arising from such nutrient-exercise interactions are discussed in the context of promoting training adaptation.
The purpose of the present study was to examine the effect of increased protein intake on short-term decrements in endurance performance during a block of high-intensity training.
Trained male cyclists (VO(2max) = 64.2 ± 6.5 mL·kg(-1)·min(-1)) completed two 3-wk trials both divided equally into normal (NOR), intensified (INT), and recovery (REC) training. In a counterbalanced crossover experimental design, cyclists received either a high-protein (PRO; 3 g protein·kg(-1) body mass (BM)·d(-1)) or a normal diet (CON; 1.5 g protein·kg(-1) BM·d(-1)) during INT and REC. Dietary carbohydrate content remained constant at 6 g·kg(-1) BM·d(-1). Energy balance was maintained during each training week. Endurance performance was assessed with a VO(2max) test and a preloaded time trial. Alterations in blood metabolite responses to exercise were measured at rest, during, and after exercise. Cyclists completed the Daily Analysis of Life Demands for Athletes (DALDA) questionnaire each day.
Increased dietary protein intake led to a possible attenuation (4.3%; 90% confidence limits ×/÷5.4%) in the decrement in time trial performance after a block of high-intensity training compared with NOR (PRO = 2639 ± 350 s; CON = 2555 ± 313 s). Restoration of endurance performance during recovery training possibly benefited (2.0%; ×/÷4.9%) from additional protein intake. Frequency of symptoms of stress described as "worse than normal" reported after a block of high-intensity training was very likely (97%) attenuated (17; ±11 AUC of "a" scores part B, DALDA for INT + REC) by increasing the protein content of the diet. No discernable changes in blood metabolite concentrations were observed in PRO.
Additional protein intake reduced symptoms of psychological stress and may result in a worthwhile amelioration of the performance decline experienced during a block of high-intensity training.
The purpose was (a) to study the effect of an 8-week Finnish military basic training period (BT) on physical fitness, body composition, mood state, and serum biochemical parameters among new conscripts; (b) to determine the incidence of overreaching (OR); and (c) to evaluate whether initial levels or training responses differ between OR and noOR subjects. Fifty-seven males (19.7 ± 0.3 years) were evaluated before and during BT. Overreaching subjects had to fulfill 3 of 5 criteria: decreased aerobic physical fitness (VO2max), increased rating of perceived exertion (RPE) in 45-minute submaximal test at 70% of VO2max or sick absence from these tests, increased somatic or emotional symptoms of OR, and high incidence of sick absence from daily service. VO2max improved during the first 4 weeks of BT. During the second half of BT, a stagnation of increase in VO2max was observed, basal serum sex hormone-binding globulin (SHBG) increased, and insulin-like growth factor-1 and cortisol decreased. Furthermore, submaximal exercise-induced increases in cortisol, maximum heart rate, and postexercise increase in blood lactate were blunted. Of 57 subjects, 33% were classified as OR. They had higher basal SHBG before and after 4 and 7 weeks of training and higher basal serum cortisol at the end of BT than noOR subjects. In addition, in contrast to noOR, OR subjects exhibited no increase in basal testosterone/cortisol ratio but a decrease in maximal La/RPE ratio during BT. As one-third of the conscripts were overreached, training after BT should involve recovery training to prevent overtraining syndrome from developing. The results confirm that serum SHBG, cortisol, and testosterone/cortisol and maximal La/RPE ratios could be useful tools to indicate whether training is too strenuous.
The present study examined whether activity energy expenditure related to body mass (AEE/kg) is associated with maximal aerobic fitness (VO(2max)), energy balance, and body mass index (BMI) during the 2 hardest weeks of the military basic training season (BT). An additional purpose was to study the accuracy of the pre-filled food diary energy intake. Energy expenditure (EE) with doubly labeled water, energy intake (EI), energy balance, and mis-recording was measured from 24 male conscripts with varying VO(2max). AEE/kg was calculated as (EE x 0.9-measured basal metabolic rate)/body mass. The reported EI was lower (P<0.001) than EE (15.48 MJ/day) and mis-recording of the pre-filled diary was -20%. The negative energy balance (-6+/-26%) was non-significant; however, the variation was high. The subjects with a low VO(2max), a high BMI, and a negative energy balance were vulnerable to low AEE/kg. However, in the multivariate regression analysis only BMI remained in the model, explaining 33% of the variation in AEE/kg. During wintertime BT, AEE/kg is affected by energy balance, VO(2max), and BMI. From these three factors, overweight limits high-level training the most. Furthermore, an optimal energy balance facilitates physical performance and enables high training loads to be sustained during the BT season.
Repeated carbohydrate feedings and caffeine have been shown to increase self-paced physical activity. Whether a field ration pack that promotes snacking of these items would enhance physical activity remains unclear.
Evaluate the effectiveness of a ration pack consisting of eat-on-move items to promote snacking, as well as caffeine items, as a nutritional strategy to improve performance.
Twenty-eight wildland firefighters consumed both an eat-on-move ration (first strike ration (FSR): 13.2 MJ, 420 g CHO, 665 mg caffeine daily) and entrée-based ration (meals, ready-to-eat (MRE): 11.9 MJ, 373 g CHO, 100 mg caffeine daily) for 2 d separated by 1 d. Diet order was counterbalanced. Outcome measurements included self-paced physical activity determined by actimetry, reaction time, number of eating occasions using dietary recall, and dietary intake from food wrapper collection.
Total eating episodes were higher with FSR compared with MRE (P = 0.013; mean +/- SD: 8.2 +/- 1.3 vs 7.6 +/- 1.1 episodes x 2 d(-1)), as were 2-d energy intake (22.0 +/- 2.4 vs 18.4 +/- 2.5 MJ; P < 0.01), carbohydrate intake (698 +/- 76 vs 546 +/- 82 mg; P < 0.01), self-reported caffeine intake (347 +/- 262 vs 55 +/- 65 mg; P < 0.01), and average end-shift salivary caffeine (1.6 +/- 1.9 vs 0.7 +/- 1.0 microg x mL(-1); P < 0.01). Total activity counts were higher (P = 0.046) when consuming FSR (507,833 +/- 129,130 counts per shift) compared with MRE (443,095 +/- 142,208 counts per shift). This was accomplished by spending a greater percentage of work shift with activity counts >1000 counts x min(-1) (21 +/- 8% vs 18 +/- 6%; P = 0.01) and less percent of work shift <50 counts x min(-1) (33 +/- 10% vs 38 +/- 10%; P = 0.01).
Delivery of energy and caffeine in a manner that promotes snacking behavior is advantageous for increasing self-selected physical activity during arduous labor.
Resting O2 consumption, net mechanical efficiency during cycling exercise and excess postexercise O2 consumption (EPOC) was measured in 15 army cadets after 3 or 4 days of continuous simulated combat exercises (estimated energy demand: 40 MJ day-1), no organized sleep and virtually no food intake (stress experiment). They exercised for 30 minutes at a work load corresponding to about 50% of maximal O2 uptake. An identical test using the same absolute work load was repeated when the cadets were completely recovered from the combat course (control experiment). Resting O2 consumption increased by 15% from 279 +/- 7 ml min-1 (control) to 320 +/- 8 ml min-1 (stress, P less than 0.001). Mechanical efficiency decreased from 24.6 +/- 0.4% (control) to 20.9 +/- 0.2% (stress, P less than 0.001). EPOC1h increased from 0.58 +/- 0.41 l (control) to 2.24 +/- 0.2% (stress, P less than 0.05). Glucose infusion during exercise (0.20 g kg-1 body weight) had no effect on mechanical efficiency or EPOC. About 1/5 of the increase in exercise O2 uptake can be explained by a substrate shift from carbohydrates to fat, as evidenced by a reduction in R-value during exercise from 0.90 +/- 0.012 (control) to 0.80 +/- 0.010 (stress). Hence, after severe physical stress combined with sleep deprivation and food restriction, O2 uptake is increased both at rest and during submaximal exercise.
The energy expenditures (EE) of 23 adult male Marines were measured during a strenuous 11-day cold-weather field exercise at 2,200- to 2,550-m elevation by both doubly labeled water (2H2 18O, DLW) and intake balance methods. The DLW EE calculations were corrected for changes in baseline isotopic abundances in a control group that did not receive 2H2 18O. Intake balance EE was estimated from the change in body energy stores and food intake. Body energy-store changes were calculated from anthropometric [-1,574 +/- 144 (SE) kcal/day] and isotope dilution (-1,872 +/- 293 kcal/day) measurements made before and after the field exercise. The subjects kept daily logbook records of ration consumption (3,132 +/- 165 kcal/day). Mean DLW EE (4,919 +/- 190 kcal/day) did not differ significantly from intake balance EE estimated from food intake and either anthropometric (4,705 +/- 181 kcal/day) or isotope dilution (5,004 +/- 240 kcal/day) estimates of the change in body energy stores. The DLW method can be used with at least the same degree of confidence as the intake balance method to measure the EE of active free-living humans.
There is a dichotomy between calories issued to soldiers in their daily field rations and the amounts actually consumed. Soldiers frequently consume insufficient calories to maintain body weight. A supplemental pack (740 kcal) was developed, to increase field calorie consumption, and tested with the old and new versions of the Meal, Ready-to-Eat on a 10-day field study in Alaska. Initial and final measurements included body weights, heights, blood, and urine parameters. Daily measurements included the collection of urine samples and completion of a dietary intake log. Energy intakes of the supplemented groups were 4%-11% higher (p less than 0.05) although the calorie intakes were still below the recommended 4,500 kcal/day for cold weather operations. Mean body weight loss ranged from 3.0 lb (1.7%) to 4.8 lb (2.8%). Two groups of the four groups became hypohydrated by day 3, due to low water intake, and only improved after direct intervention to increase drinking. Water and food intakes were strongly correlated (p less than 0.05). Results confirm the success of the supplemental pack as a means of increasing food intake and underscore the importance of water discipline in a cold environment.
A survey of U.S. Marines was conducted in order to investigate the effect of combat, a highly stressful situation, on eating behavior. The results indicate that Marines reduced their food intake, especially during their first combat experience. The principle reason cited for reduced consumption during combat was the lack of time to eat and prepare food. However, fear was important in accounting for reduced consumption during the marines' initial exposure to combat. The results are consistent with other laboratory and survey findings that stress leads to a reduction in food intake.
To test the application of doubly labeled water under adverse field conditions, energy expenditures of 16 special operations soldiers were measured during a 28-day field training exercise. Subjects were matched by fat-free mass and divided equally between an ad libitum ready-to-eat meal diet and a 2,000 kcal/day lightweight ration. Subjects recorded intakes daily, and body composition was measured before and after the exercise. At the beginning of the study, subjects moved to a new northerly location and, therefore, a new water supply. To compensate for this, a group of soldiers who did not receive heavy water was followed to measure isotopic base-line changes. Energy expenditure by doubly labeled water was in agreement with intake/balance (3,400 +/- 260 vs. 3,230 +/- 520 kcal/day). The overall coefficient of variation of energy expenditure by doubly labeled water was half that of intake/balance (7.6 vs. 16.1%). The coefficient of variation of repeat measures with doubly labeled water was 7.3%. Energy expenditure of the ready-to-eat meal group, 3,540 +/- 180 kcal/day, was not significantly different from the lightweight ration group, 3,330 +/- 301 kcal/day. Doubly labeled water was valid under field conditions.
The deuterium oxide elimination method for measuring average daily milk intake was validated against measured formula intake in 16 studies of 11 infants in a metabolic ward. Deuterium oxide (approximately 0.10 g/kg body wt) was given orally. Deuterium enrichment was measured in urine samples collected predose, as available for 6-h postdose for TBW determination, and at 24 h and 5-10 d postdose for HDO elimination calculated according to the two-point method. Urine samples were vacuum distilled, water was reduced to hydrogen gas, and deuterium enrichment was measured by isotope-ratio mass spectrometry. Milk intake was measured throughout the elimination period from prefeeding and postfeeding bottle weights (n = 12) or volumes (n = 4). Without corrections for atmospheric water influx, milk intake was overestimated by 76 g/d (6%). With corrections for estimated metabolic water production, isotopic fractionation, and atmospheric water influx, deuterium measured 98% +/- 3% or 1300 g milk intake/d compared with actual milk intake of 1329 +/- 206 g/d.
The effects of three weight reduction methods on maximal strength, rate of force development, vertical jumping height, and mechanical power were studied in track and field athletes and volleyball players. The three methods were sauna, diet with diuretic, and diuretic alone. The reductions in weight achieved were 3.4%, 5.8%, and 3.8% of body weight after sauna, diet + diuretic, and diuretic, respectively (P less than 0.001). Maximal isometric leg strength and the rate of isometric force development were decreased after the sauna and diet + diuretic treatments. Dehydration caused by the diuretic method alone did not impair neuromuscular performances. As had been expected from theoretical calculations, the rise of the body center of gravity in vertical jumping was slightly improved with all three treatments, the improvement being the greatest following the diuretic treatment (7.1%, P less than 0.001). However, when the work performed was extended for 15 s, an improved power output could be observed only with the diet + diuretic treatment (P less than 0.01). No explanation for the results observed could be made in terms of physiologic parameters.
A group of 24 men was studied during a period of heavy, sustained work lasting for 107 hours, during which time they had less than 2 hours sleep. Nine men received a diet providing 33·49 MJ (8000 kcal) and 15 a diet providing 6·30 MJ (1500kcal) per day. The subjects were assessed by objective measurements of simulated military tasks and by subjective assessments using self-rated (Borg perceived exertion and Standford sleepiness scales) and observer-rated scales. Although the high energy group tended to feel slightly more alert there were no differences between the group in the tests of military performance. After 4 days of sustained activity all subjects were judged to be ineffective as soldiers. The high-energy diet was well tolerated. The average loss of body-fat in the high-energy group was 1·3 kg compared with 3·1 kg in the other group, suggesting that even the high-energy group was in energy deficit. These results suggest that the major factor influencing performance in these experiments was sleep deprivation, and that the decline in performance as assessed by observers, could not be prevented by giving a high-energy diet alone.
An update of practical aspects of the use of labeled water for the measurement of total body water (TBW) and energy expenditure (EE) is presented as applied in Maastricht, The Netherlands. We use a 10-hour equilibration period. The isotopes for the measurement of TBW and EE are routinely administered, after collecting a background urine sample, as a last consumption before the night. Our data show an underestimate of TBW measured with isotope dilution after 4 hours (in the morning), a discrepancy which increases with the size of TBW. No such relation and no significant differences were found after 10-hour (overnight) equilibration. The ratio between the dilution space for deuterium and oxygen-18 is higher than the earlier figure of 1.03, especially in adult subjects with a high body fat content. For an observation period of EE over two weeks, samples from the second and the last voiding on the first, mid, and last day of the observation period are collected. Differences in EE calculated from morning and evening samples within the first and second week allow detection of sampling errors and if so, samples are excluded from the final calculation. Differences of EE between weeks 1 and 2 allow a check for the consistency of the subjects' physical activity level and usually fall within 10% of the average EE over the total observation interval.
The 24-h energy expenditure (24-h EE), resting EE (REE), sleeping EE (SEE), and spontaneous physical activity (SPA) were compared between six male endurance athletes whose reported energy intake was low (LOW) and did not match that theoretically required for weight maintenance and four whose reported energy intake appeared adequate (ADQ) and matched their estimated EE. Groups did not differ in age, body weight, fat-free mass, and daily EE estimated from activity records. The LOW athletes reported an energy intake 6338 +/- 2164 kJ.d-1 less than estimated EE. The 24-h EE, REE, SEE, and SPA of the LOW athletes were significantly lower than the ADQ athletes (862, 523, 770 kJ.d-1, and 43 min.d-1, respectively). Using all subjects, there was a significant positive correlation between REE and free thyroxine (FT4) (r = 0.82) and SEE and FT4 (r = 0.66). Thus, part of the LOW athlete's ability to maintain body weight on a seemingly low energy intake appears due to a lower daily sedentary EE.
Athletes reduce bodyweight for several reasons: to compete in a lower weight class; to improve aesthetic appearance; or to increase physical performance. Rapid bodyweight reduction (dehydration in 12 to 96 hours), typically with fluid restriction and increased exercise, is used by athletes competing in weight-class events. Gradual bodyweight reduction (over >1 week) is usually achieved by cutting energy intake to 75 to 130 kJ/kg/day. An intake of 100 kJ/kg/day results in a weekly bodyweight loss of roughly 1kg. Aerobic endurance capacity decreases after rapid bodyweight reduction, but might increase after gradual bodyweight reduction. Maximal oxygen uptake (V̇O2max) measured as L/min is unchanged or decreased after bodyweight loss, but V̇O2max measured as ml/kg/min may increase after gradual bodyweight reduction. Anaerobic performance and muscle strength are typically decreased after rapid bodyweight reduction with or without 1 to 3 hours rehydration. When tested after 5 to 24 hours of rehydration, performance is maintained at euhydrated levels. A high carbohydrate diet during bodyweight loss may help in maintaining performance. Anaerobic performance is not affected and strength can increase after gradual bodyweight reduction. Reductions in plasma volume, muscle glycogen content and the buffer capacity of the blood explain decreased performance after rapid bodyweight reduction. During gradual bodyweight loss, slow glycogen resynthesis after training, loss of muscle protein and stress fractures (caused by endocrinological disorders) may affect performance. Athletes’ bodyweight goals should be individualised rather than by comparing with other athletes. If the time between weigh-in and competition is
Physical performance of military tasks can deteriorate during field training.
Drinking a carbohydrate-electrolyte (CHO-E) beverage during military relevant training would improve fluid and caloric intake, and better sustain physical performance.
Some 27 volunteers restricted to approximately 2600 kcal.d-1 were randomly assigned to one of three groups: CHO-E, placebo, or water. Fluid intake was ad libitum. The volunteers completed 3 d of field training in hot humid conditions (30 degrees C, 60% rh). Training days 1 and 2 each included a 16-21 km march over hilly terrain, marksmanship training, and 2 h of rock climbing. Day 3 included a 14.5 km march followed by marksmanship tests, a timed rock climb and a 0.7 km uphill (21% grade) run.
The CHO-E beverage provided an additional approximately 2800 kcal (p < 0.05) for the 3 d of training. There were no differences (ANOVA, p > 0.05) between the groups absolute or changes from pre-training values for fluid intake, body weight, climb time, run time, marksmanship, or mood. Those drinking CHO-E were, however, more likely to maintain uphill run performance after training (chi 2 = 7.2; p < 0.05) and more likely to maintain both uphill run and marksmanship ability (chi 2 = 17.2; p < 0.05). There was also an inverse relationship between caloric intake and deterioration of uphill run performance (r = -0.75; p < 0.05).
Persons drinking CHO-E or practicing good food discipline are more likely to sustain physical performance than those eating only a portion of their food. CHO-E provides an accessible source of calories which can be advantageous when limited food is available or inadaquate food consumption is likely.
Nutritional intake by military personnel is typically inadequate during field exercises, potentially compromising health and performance.
Drinking a supplemental carbohydrate (CHO) beverage will increase total caloric intake and maintain nutritional status during military training in the desert.
A total of 63 volunteers were randomly assigned to one of two groups to receive either a CHO or placebo beverage with military rations during an 11-d desert field exercise. Fluid intake was ad libitum and adequate rations were provided. Blood samples were collected twice to assess nutritional status, and nutrient intake was determined with consumption data. Mood state was examined by questionnaire.
Energy intake was significantly higher in the CHO group (3050 kcal x d(-1) vs. 2631 kcal x d(-1)), with additional CHO from the beverage providing energy with some compensation by reduced fat and protein intake. Intakes of energy, folacin, calcium, magnesium, iron, and zinc in both groups were inadequate, with intakes significantly lower (p<0.05) for calcium, magnesium, and zinc in the CHO beverage group. Blood parameters of nutritional status remained within normal ranges with no differences between groups, but significant decreases were seen in pre-albumin. No changes in mood were seen during the training, nor after exposure to desert conditions.
The operational ration supplemented with a CHO beverage significantly increases CHO and energy intakes compared with standard rations and maintains nutritional status for short exercises. Fortification with micronutrients most at risk for deficient intake from foods may be needed for longer deployments.
We studied the effect of moderate, short-term energy restriction on physical performance in physically fit men (n = 13) and women (n = 11) in a controlled clinical research setting with a metabolic kitchen, exercise testing laboratory and training facility. The experiment consisted of a 10 d baseline period followed by either 2 wk of dietary energy restriction (750 kcal/d; n = 16) or energy balance (control; n = 8). During this 24 day study, exercise energy expenditure averaged 465 +/- 5.7 kcal/d in all subjects and was accomplished through treadmill running at a self-selected pace. Body weight was maintained in the control group (-0.36 +/- 0.24kg), but energy restriction resulted in weight loss of -1.29 +/- 0.16 kg (p < 0.001). There was a trend for lean body mass to decline more in the energy restriction group (p = 0.093), accounting for 61% of the weight loss, and urinary nitrogen excretion also tended to be higher in the energy restriction vs. control group (i.e., 13.2 +/- 1.1 vs. 11.2 +/- 1.0g/d; p = 0.089). Muscle strength (leg & shoulder press; 1 repetition maximum) was maintained or increased during the energy restriction period. Muscle endurance, assessed by leg squats to fatigue, and 5 mile run time improved following two weeks of energy restriction or balance. Anaerobic capacity (Wingate Test) increased slightly in the restriction (+ 368 +/- 219 joules) but declined in the control group 649 +/- 288 joules; p<0.05). We conclude that short-term (2 weeks) moderate energy restriction (approximately 750 kcal/d) results in weight loss but does not impair performance in physically fit young men and women.
Athletes are exposed to acute and chronic stress that may lead to suppression of the immune system and increased oxidative species generation. In addition, the tendency to consume fewer calories than expended and to avoid fats may further compromise the immune system and antioxidant mechanisms. The exercise stress is proportional to the intensity and duration of the exercise, relative to the maximal capacity of the athlete. Muscle glycogen depletion compromises exercise performance and it also increases the stress. Glycogen stores can be protected by increased fat oxidation (glycogen sparing). The diets of athletes should be balanced so that total caloric intake equals expenditure, and so that the carbohydrates and fats utilised in exercise are replenished. Many athletes do not meet these criteria and have compromised glycogen or fat stores, have deficits in essential fats, and do not take in sufficient micronutrients to support exercise performance, immune competence and antioxidant defence. Either overtraining or under nutrition may lead to an increased risk of infections. Exercise stress leads to a proportional increase in stress hormone levels and concomitant changes in several aspects of immunity, including the following: high cortisol; neutrophilia; lymphopenia; decreases in granulocyte oxidative burst, nasal mucociliary clearance, natural killer cell activity, lymphocyte proliferation, the delayed-type sensitivity response, the production of cytokines in response to mitogens, and nasal and salivary immunoglobulin A levels; blunted major histocompatibility complex II expression in macrophages; and increases in blood granulocyte and monocyte phagocytosis, and pro- and anti-inflammatory cytokines. In addition to providing fuel for exercise, glycolysis, glutaminlysis, fat oxidation and protein degradation participate in metabolism and synthesis of the immune components. Compromising, or overusing, any of these components may lead to immunosuppression. In some cases, supplementation with micronutrients may facilitate the immune system and compensate for deficits in essential nutrients. In summary, athletes should eat adequate calories and nutrients to balance expenditure of all nutrients. Dietary insufficiencies should be compensated for by supplementation with nutrients, with care not to over compensate. By following these rules, and regulating training to avoid overtraining, the immune system can be maintained to minimise the risk of upper respiratory tract infections.
This study compared a light meal combat ration (LMCR) to specific commercial sport drinks (CSD) and the effect of their ingestion on time to exhaustion during simulated combat maneuvers (SCM). The SCM consisted of three activities: a 2-hour march at 50% of maximal aerobic capacity (VO2max); a subsequent 1-hour run at 70% VO2max; and a run to exhaustion at 80% VO2max. During SCM, the subjects consumed one of four different meals: three CSD (Ergo, Go Sports, and Gatorlode), and the LMCR. In addition, one SCM was conducted with half-rations. Oxygen consumption, heart rate, and rating of perceived exertion were evaluated during each phase of the SCM. Time in minutes (mean +/- SD) to exhaustion at 80% VO2max for Ergo (42.3 +/- 8.9), Go Sports (39.4 +/- 13.3), and Gatorlode (37.7 +/- 8.6) was not significantly different from that for LMCR (36.4 +/- 13.0) but was greater than that for half-LMCR (30.3 +/- 9.3). O2 consumption, heart rate, and rating of perceived exertion were not affected by meal type but did increase over time for each stage of the SCM. We conclude that the amount of calories ingested was responsible for the differences noted in time to exhaustion. We further conclude that the CSD represent a readily available source of energy and fluid that could be used to replace and/or supplement the current LMCR.
To characterize the impact of prolonged work, underfeeding, and sleep deprivation (i.e., sustained operations; SUSOPS) on physical and occupational related performance during military operational stress.
Ten male soldiers were tested on days 1 (D1), 3 (D3), and 4 (D4) of a control and an experimental week that included prolonged physical work (total daily energy expenditure approximately 4,500 kcal x d(-1)), underfeeding (approximately 1,600 kcal x d(-1)), and sleep deprivation (approximately 2 h x d(-1)). Body composition was measured with dual-energy x-ray absorptiometry (DEXA). Ballistic power was assessed by 30 repetitive squat jumps and bench-press throws. Military-relevant occupational performance was evaluated with a 10-min box lift, obstacle course, grenade throw, rifle marksmanship, and a 25-min wall-build task.
Fat-free mass (-2.3%) and fat mass (-7.3%) declined (P </= 0.05) during SUSOPS. Squat-jump mean power (-9%) and total work (-15%) declined (P </= 0.05) during SUSOPS. Bench-press power output, grenade throw, and marksmanship for pop-up targets were not affected. Obstacle course and box-lift performances were lower (P </= 0.05) on D3 but showed some recovery on D4. Wall building was approximately 25% lower (P </= 0.05) during SUSOPS.
Decrements in performance during SUSOPS are primarily restricted to tasks that recruit muscles that are over-utilized without adequate recovery. General military skill tasks and occupational physical performance tasks are fairly well maintained.
Elevated postexercise amino acid availability has been demonstrated to enhance muscle protein synthesis acutely, but the long-term impact of postexercise protein supplementation on variables such as health, muscle soreness, and function are unclear. Healthy male US Marine recruits from six platoons (US Marine Corps Base, Parris Island, SC; n = 387; 18.9 +/- 0.1 yr, 74.7 +/- 1.1 kg, 13.8 +/- 0.4% body fat) were randomly assigned to three treatments within each platoon. Nutrients supplemented immediately postexercise during the 54-day basic training were either placebo (0 g carbohydrate, 0 g protein, 0 g fat), control (8, 0, 3), or protein supplement (8, 10, 3). Subjects and observers making measurements and data analysis were blinded to subject groupings. Compared with placebo and control groups, the protein-supplemented group had an average of 33% fewer total medical visits, 28% fewer visits due to bacterial/viral infections, 37% fewer visits due to muscle/joint problems, and 83% fewer visits due to heat exhaustion. Recruits experiencing heat exhaustion had greater body mass, lean, fat, and water losses. Muscle soreness immediately postexercise was reduced by protein supplementation vs. placebo and control groups on both days 34 and 54. Postexercise protein supplementation may not only enhance muscle protein deposition but it also has significant potential to positively impact health, muscle soreness, and tissue hydration during prolonged intense exercise training, suggesting a potential therapeutic approach for the prevention of health problems in severely stressed exercising populations.
Twenty years of testing in the field has consistently revealed that food intake is inadequate when packaged military rations are fed as the sole source of food. Food intake is much lower and there is a loss of body weight. Conversely when these rations are fed to students or military personnel for periods ranging from 3 to 42 days in a cafeteria-like setting, food intake is comparable to levels of a control group provided with freshly prepared food. Under these conditions, body weight is maintained. In this review, the consumption pattern is considered in terms of characteristics of the food (acceptability, variety, portion size, beverages, serving temperature, appropriateness for time of day, monotony, and novelty) and the eating milieu (social interactions, time, ease of preparing and consuming a meal). The twenty-year program of military ration research has led us to conclude that both the food and the context must be considered in understanding and controlling food intake.
Laboratory data with single exposures showed that palatability has a positive relationship with food intake. The question addressed in this study is whether this relationship also holds over repeated exposures in non-laboratory contexts in more natural environments. The data were collected in four field studies, lasting 4-11 days with 307 US Army men and 119 Army women, and comprised 5791 main meals and 8831 snacks in total. Acceptability was rated on the nine point hedonic scale, and intake was registered in units of 1/4, 1/2, 3/4, or 1 or more times of the provided portion size. Correlation coefficients between individual acceptability ratings and intakes varied from 0.22 to 0.62 for the main meals (n=193-2267), and between 0.13 and 0.56 for the snacks (n=304-2967). The likelihood of choosing a meal for the second time was positively related to the acceptability rating of the meal when it was consumed for the first time. The results reinforce the importance of liking in food choice and food intake/choice behavior. However, the magnitude of the correlation coefficients between acceptability ratings and food intake suggest that environmental factors also have an important role in determining intake and choice.
Military exercises generate high levels of stress to simulate combat, providing a unique opportunity to examine cognitive and physiologic responses of normal humans to acute stress.
Cognitive and physiologic markers of stress were evaluated before, during, and after an intense training exercise conducted for 53 hours in the heat. Cognitive performance, mood, physical activity, sleep, body composition, hydration, and saliva cortisol, testosterone, and melatonin were assessed. Volunteers were 31 male U.S. Army officers from an elite unit, aged 31.6 +/- .4 years.
Wrist activity monitors documented that soldiers slept only 3.0 +/- .3 hours during the exercise and were active throughout. Volunteers lost 4.1 +/- .2 kg (p < .001) of weight, predominately water (3.1 +/- .3 L) (p < .001). Substantial degradation in cognitive function, assessed with computerized tests, occurred. Vigilance, reaction time, attention, memory, and reasoning were impaired (p < .001). Mood, including vigor (p < .001), fatigue (p < .001), confusion (p < .001), depression (p < .001), and tension (p < .002), assessed by questionnaire, deteriorated. The highest cortisol and testosterone levels were observed before the exercise.
This study quantifies the overwhelmingly adverse impact of multiple stressors on cognitive performance, mood, and physiologic parameters, during a continuous but brief military exercise conducted by highly motivated, well-trained officers.
Although water is an important nutrient, there are no recommended intake values. Here, water intake, energy intake, physical activity and water loss was measured over 1 week in summer and in winter. Subjects were healthy volunteers, forty-two women and ten men, mean age of 29 (SD 7) years and mean BMI 21.8 (SD 2.2) kg/m2. Water intake was measured with a 7 d food and water record. Physical activity level (PAL) was observed as the ratio of total energy expenditure, as measured with doubly labelled water, to resting energy expenditure as measured in a respiration chamber. Water loss was measured with the deuterium elimination method. Water loss was highly reproducible and ranged from 0.20 to 0.35 l/MJ, independent of season and activity level, with higher values in women. Water loss was related to water and energy intake in summer (r 0.96, P<0.0001 and r 0.68, P<0.001, respectively) as well as in winter (r 0.98, P<0.0001 and r 0.63, P<0.01, respectively). Water loss was, for men, higher in subjects with a higher physical activity in summer (r 0.94, P<0.0001) and in winter (r 0.70, P<0.05). Normalizing water loss for differences in energy expenditure by expressing water loss in litres per MJ resulted in the same value for men in summer and winter. For women, physical activity-adjusted values of water loss were higher, especially in summer. In men, water turnover was determined by energy intake and physical activity, while seasonal effects appeared through energy expenditure. Women showed a higher water turnover that was unrelated to physical activity.
To assess reliability, responsiveness, importance to patients, and convergent validity for the Wisconsin Upper Respiratory Symptom Survey (WURSS-44) and to develop a short-form WURSS.
Community-based recruitment of participants with colds. Prospective monitoring from within 48 hours of first symptom until 2 days after end of cold. The WURSS-44 includes 1 global illness severity item, 32 symptom-based items, 10 functional quality-of-life items, and 1 item assessing global change. The SF-36, SF-8, and the Jackson cold scale were used as external comparators.
Participants included 104 women and 45 men, aged 18 to 80 years, self-reporting on 1,681 person-days of illness. Factor analysis suggested 10 dimensions, with reliability coefficients from 0.62 to 0.93. Comparing daily WURSS-44 to Jackson and SF-8 yielded Pearson correlation coefficients from 0.73 to 0.93, and from -0.60 to -0.84, respectively. Importance to patients and responsiveness assessment yielded a short version, the WURSS-21. Guyatt's responsiveness index was 0.54 for the SF-8, 0.61 for the Jackson, 0.71 for the WURSS-44, and 0.80 for the WURSS-21, suggesting that a two-armed trial would require 74 participants for the WURSS-21, 92 for the WURSS-44, 124 for the Jackson scale, and 156 for the SF-8.
The construct validity of WURSS-44 is supported by measures of reliability, responsiveness, importance to patients, and convergence. A shorter version, the WURSS-21, may be even more responsive.
Ad libitum, low-carbohydrate diets decrease caloric intake and cause weight loss. It is unclear whether these effects are due to the reduced carbohydrate content of such diets or to their associated increase in protein intake.
We tested the hypothesis that increasing the protein content while maintaining the carbohydrate content of the diet lowers body weight by decreasing appetite and spontaneous caloric intake.
Appetite, caloric intake, body weight, and fat mass were measured in 19 subjects placed sequentially on the following diets: a weight-maintaining diet (15% protein, 35% fat, and 50% carbohydrate) for 2 wk, an isocaloric diet (30% protein, 20% fat, and 50% carbohydrate) for 2 wk, and an ad libitum diet (30% protein, 20% fat, and 50% carbohydrate) for 12 wk. Blood was sampled frequently at the end of each diet phase to measure the area under the plasma concentration versus time curve (AUC) for insulin, leptin, and ghrelin.
Satiety was markedly increased with the isocaloric high-protein diet despite an unchanged leptin AUC. Mean (+/-SE) spontaneous energy intake decreased by 441 +/- 63 kcal/d, body weight decreased by 4.9 +/- 0.5 kg, and fat mass decreased by 3.7 +/- 0.4 kg with the ad libitum, high-protein diet, despite a significantly decreased leptin AUC and increased ghrelin AUC.
An increase in dietary protein from 15% to 30% of energy at a constant carbohydrate intake produces a sustained decrease in ad libitum caloric intake that may be mediated by increased central nervous system leptin sensitivity and results in significant weight loss. This anorexic effect of protein may contribute to the weight loss produced by low-carbohydrate diets.
This study reviews historical and biomedical aspects of soldier load carriage. Before the 18th century, foot soldiers seldom carried more than 15 kg while on the march, but loads have progressively risen since then. This load increase is presumably due to the weight of weapons and equipment that incorporate new technologies to increase protection, firepower, communications, and mobility. Research shows that locating the load center of mass as close as possible to the body center of mass results in the lowest energy cost and tends to keep the body in an upright position similar to unloaded walking. Loads carried on other parts of the body result in higher energy expenditures: each kilogram added to the foot increases energy expenditure 7% to 10%; each kilogram added to the thigh increases energy expenditure 4%. Hip belts on rucksacks should be used whenever possible as they reduce pressure on the shoulders and increase comfort. Low or mid-back load placement might be preferable on uneven terrain but high load placement may be best for even terrain. In some tactical situations, combat load carts can be used, and these can considerably reduce energy expenditure and improve performance. Physical training that includes aerobic exercise, resistance training targeted at specific muscle groups, and regular road marching can considerably improve road marching speed and efficiency. The energy cost of walking with backpack loads increases progressively with increases in weight carried, body mass, walking speed, or grade; type of terrain also influences energy cost. Predictive equations have been developed, but these may not be accurate for prolonged load carriage. Common injuries associated with prolonged load carriage include foot blisters, stress fractures, back strains, metatarsalgia, rucksack palsy, and knee pain. Load carriage can be facilitated by lightening loads, improving load distribution, optimizing load-carriage equipment, and taking preventive action to reduce the incidence of injury.
Upper respiratory illness (URI) is the most common medical condition affecting elite athletes. The aims of this study were to identify and evaluate the incidence, pathogenic etiology, and symptomatology of acute URI during a 5-month training and competition period.
Thirty-two elite and 31 recreationally competitive triathletes and cyclists, and 20 sedentary controls (age range 18.0-34.1 yr) participated in a prospective surveillance study. Nasopharyngeal and throat swabs were collected from subjects presenting with two or more defined upper respiratory symptoms. Swabs were analyzed using microscopy, culture, and PCR testing for typical and atypical respiratory pathogens. The Wisconsin Upper Respiratory Symptom Survey (WURSS-44) was used to assess symptomatology and functional impairment.
Thirty-seven URI episodes were reported in 28 subjects. Incidence rate ratios for illness were higher in both the control subjects (1.93, 95% CI: 0.72-5.18) and elite athletes (4.50, 1.91-10.59) than in the recreationally competitive athletes. Infectious agents were identified in only 11 (two control, three recreationally competitive, and six elite) out of 37 illness episodes. Rhinovirus was the most common respiratory pathogen isolated. Symptom and functional impairment severity scores were higher in subjects with an infectious pathogen episode, particularly on illness days 3-4.
The results confirm a higher rate of URI among elite athletes than recreationally competitive athletes during this training and competition season. However, because pathogens were isolated in fewer than 30% of URI cases, further study is required to uncover the causes of unidentified but symptomatic URI in athletes. Despite the common perception that all URI are infections, physicians should consider both infectious and noninfectious causes when athletes present with symptoms.