Lean body mass estimation by bioelectrical impedance analysis: a four-site cross-validation study.

This study validated further the bioelectrical impedance analysis (BIA) method for body composition estimation. At four laboratories densitometrically-determined lean body mass (LBMd) was compared with BIA in 1567 adults (1069 men, 498 women) aged 17-62 y and with 3-56% body fat. Equations for predicting LBMd from resistance measured by BIA, height, weight, and age were obtained for the men and women. Application of each equation to the data from the other labs yielded small reductions in R values and small increases in SEEs. Some regression coefficients differed among labs but these differences were eliminated after adjustment for differences among labs in the subjects' body fatness. All data were pooled to derive fatness-specific equations for predicting LBMd: the resulting R values ranged from 0.907 to 0.952 with SEEs of 1.97-3.03 kg. These results confirm the validity of BIA and indicate that the precision of predicting LBM from impedance can be enhanced by sex- and fatness-specific equations.

Use of bioelectrical impedance analysis measurements as predictors of physical performance.

Through its association with fat-free mass (FFM), bioelectrical impedance analysis (BIA) offers an alternative to physical performance testing. We examined the relations between stature2/resistance (S2/R), FFM, and muscular strength in data from three studies of young military men and women. Resistance was measured at 50 kHz by using the conventional tetrapolar electrode method. FFM was based on skinfold thicknesses, and estimated with the regression equations of Durnin and Womersley. Strength was measured as a one-repetition maximum on an incremental lift test (IL1RM), which is widely used by the military services to predict overall body strength. Although there was an association between IL1RM and S2/R in each of these studies (correlations ranged from 0.35 to 0.53), correlations were strongest between FFM and S2/R (R = 0.53 to 0.85), indicating that BIA and FFM derived from skinfold thicknesses are better correlated with each other than are the relations of either of these with physical performance. Modest increases in FFM and strength in one 8-wk training study correlated with S2/R; however, large decreases in FFM and strength in another study (with weight losses of 10 kg in 8 wk) were not reflected by changes in S2/R. Thus, BIA is not particularly useful for performance prediction despite its moderate relation to FFM. BIA is especially problematic with large changes in body composition, for which there are apparent deviations in hydration status; expedient methods such as skinfold predictions will be more resistant to such effects.

Plasma adrenocorticotropin and cortisol responses to brief high-intensity exercise in humans.

The purpose of this study is to examine plasma cortisol and adrenocorticotropin (ACTH) levels following a brief high-intensity bout of exercise. Each subject (n = 6) performed a 1-min bout of exercise on a cycle ergometer at 120% of his maximum O2 uptake. Blood samples were collected at rest, immediately following the exercise bout, and at 5, 15, and 30 min postexercise. Mean (+/- SE) plasma ACTH levels increased significantly (P less than 0.05) from 2.2 +/- 0.4 pmol/l at rest to 6.2 +/- 1.7 pmol/l immediately following exercise. Mean (+/- SE) plasma cortisol levels increased significantly from 0.40 +/- 0.04 mumol/l at rest to 0.52 +/- 0.04 mumol/l at 15 min postexercise. These data show that brief high-intensity exercise results in significant increases in plasma cortisol and ACTH levels. Furthermore, the temporal sequence between the two hormones suggests that the increase in plasma cortisol levels following brief high-intensity exercise is the result of ACTH-induced steroidogenesis in the adrenal cortex.

Cold exposure during military operations: effects on anaerobic performance.

This study examined the effects of military field operations (MFO) under different environmental conditions on anaerobic performance. US Marines were tested in the field under the following conditions: 1) noncold environment (NC; n = 30, 10-32 degrees C) and 2) cold environment (CO; n = 32, -2 to -22 degrees C). Subjects performed 30-s Wingate tests (WIN) pre- and immediately post-MFO to assess anaerobic performance. The MFO consisted of approximately 4.5 days of combat training maneuvers while carrying field equipment (packs and weapon, approximately 25 kg). WIN measures obtained were absolute and relative mean power (MP), 5-s peak power (PP), and fatigue index (% decline). Significant main effects (P less than 0.01) were observed for time (pre-post MFO). Reductions occurred in absolute MP [651.8 +/- 30.3 to 616.4 +/- 28.5 (SE) W] and PP (897.8 +/- 41.6 to 857.0 +/- 39.1 W); however, no effect on fatigue index was seen. Significant interaction effects (P less than 0.05) were observed in relative measures. Reductions (pre-post) in MP (NC = 8.64 +/- 0.16 to 8.37 +/- 0.14 W/kg; CO = 8.91 +/- 0.26 to 8.04 +/- 0.15 W/kg) and PP (NC = 11.80 +/- 0.24 to 11.61 +/- 0.33 W/kg; CO = 12.23 +/- 0.35 to 11.20 +/- 0.19 W/kg) were greater under CO than NC conditions. These changes were found despite significant (P less than 0.05) but comparable pre-post weight reductions in both CO and NC conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of fatigue on joint position sense of the knee.

This study was designed to test position sense of the knee joint before and after fatigue in order to determine whether muscle or capsular receptors are the primary sensors for joint position sense. Reproduction of passive positioning and detection of the onset of motion (kinesthesia) were employed to measure joint position sense. Eleven subjects underwent joint position sense measurement before and after a fatigue protocol. A significant worsening of reproduction of knee joint angle after fatigue was noted (p less than 0.05). Threshold (kinesthesia) showed no statistically significant change after fatigue. A significant correlation of reproduction measurements and threshold measurements prior to fatigue (p less than 0.01) demonstrated that the same neural mechanism is applicable in the rested state, but these variables did not correlate significantly after fatigue. There was a significant correlation between reproduction measurements before and after fatigue (p = 0.018), while no correlation was seen for the pre- and postfatigue threshold measurements, suggesting a change in the neural path after fatigue. Since both tests of joint position sense are affected by fatigue, we conclude that muscle receptors are a prominent, if not primary, determinant of joint position sense, and capsular receptors may have a secondary role. Reproduction ability is decreased, presumably through the loss of efficiency of muscle receptors. The threshold data suggest a change in the mechanism of appreciation after fatigue, possibly due to increased sensitivity of capsular receptors from muscle-fatigue-induced laxity.

Aerobic/calisthenic and aerobic/circuit weight training programs for Navy men: a comparative study.

Study I. Participants were 43 Navy men (mean age = 32.1 yr) assigned to one of three exercise training protocols: aerobic/circuit weight training performed at either 40 or 60% of determined one-repetition maximum strength or aerobic/calisthenic training. During the 10-wk study, each exercise group participated in three training sessions per week performed on alternate days. The results of this study indicate that dynamic strength (both upper and lower) increased for the aerobic/circuit weight training groups but not for the aerobic/calisthenic group. With the exception of bench press endurance for the aerobic/calisthenic group, all groups showed significant increases in muscular endurance and stamina. No significant changes were seen in static strength or flexibility in any of the groups. Study II. Subjects were 87 male Navy personnel (mean age = 19.8 yr) receiving basic training at the Recruit Training Command, San Diego, CA. One company of recruits (N = 41) participated in an experimental aerobic/circuit weight training program at 70% of determined one-repetition maximum. A second company (N = 46) received the standard Navy recruit physical training program (aerobic/calisthenic training). During the 8-wk study, both groups participated in an identical running program performed three times per wk on alternate days. Additionally, aerobic/circuit weight training participants completed two circuits (1 circuit = 15 exercises) three times per wk on alternate days to running. Study findings show the experimental aerobic/circuit weight training program produced significantly greater dynamic muscular strength and muscular endurance changes than the standard aerobic/calisthenic program.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise-related knee joint laxity.

Knee injuries are the topic of increasingly sophisticated research because of the importance in professional athletics as well as increasing participation in recreational sports. The role of conditioning and fatigue in these injuries remains controversial. Ligaments have high collagen content, and a viscoelastic response to stress would be expected. Because of the postulated relationship between laxity and knee ligament injuries, an experiment was designed using highly motivated athletes to test the hypothesis that exercise to the point of muscular fatigue may cause laxity of the knee and thereby place athletes at risk for ligamentous injury to the knee when fatigued. An exercise protocol was designed to produce muscle fatigue in the hamstring and quadriceps muscle groups. Knee ligament laxity was tested prior to and subsequent to the exercise protocol. To document muscle fatigue, isokinetic testing of right knee flexion and extension power was used several times during the exercise protocol. A knee arthrometer (KT-1000) was used to quantitatively document ligamentous laxity before and after exercise. The results indicated a significant lengthening in knee joint laxity between preexercise and postexercise in the left knee as measured at 15 and 20 pounds of passive displacement force (P less than 0.05). Maximum manual displacement also demonstrated a significant increase in joint laxity (P = 0.02). The right knee, which had undergone isokinetic testing, demonstrated a similar tendency but without a statistically significant difference before and after exercise. There was no significant preexercise side to side difference, but postexercise measurements demonstrated a left-right difference at 15 pounds, 20 pounds, and maximum manual displacement of statistical significance (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Validity and reliability of a timed 5 km cycle ergometer ride to predict maximum oxygen uptake.

The purpose of this study was to determine the validity and reliability of a timed 5 km cycle ergometer ride to predict maximum oxygen uptake (VO2max). Fifty-two healthy volunteers had their VO2max determined during a maximal treadmill run. They also performed a timed 5 km cycle ergometer ride. The resistance setting for the cycle ride was set at a rate of 0.5 kg/20 kg body weight. A significant inverse relationship was found between the logarithm of cycle time and VO2max (r = -0.83). Furthermore, the test-retest reliability for the 5 km ride was determined to be r = 0.93 (n = 20). These results suggest that a timed 5 km cycle ergometer ride is a valid and reliable predictor of VO2max. Furthermore, the timed cycle ride offers several methodological advantages which makes it potentially useful in clinical, military, and research settings.

Thyroid hormone changes during military field operations: effects of cold exposure in the Arctic.

This study examined the effect of prolonged physical activity in a cold environment upon circulating thyroid hormone levels. A secondary focus of the study involved the role of nocturnal habitat upon the thyroidal responses to the physical activity and cold exposure. Military personnel exposed to 10 d of field-based operations in the arctic region of Norway were studied. Blood samples were collected before (day 1), and at days 5 and 10 of the operations. Levels of total T4, free T4, total T3, free T3, and thyroid binding globulin were assessed in all blood samples. The results indicated considerable, significant (p less than 0.05) decreases in total thyroid hormone levels, while relative increases of free fractions of the hormones occur with the 10-d operations in the Arctic. However, no significant influence on thyroidal responses were observed due to the nocturnal habitat that the subjects lived in. The hormonal alterations noted are possibly brought about by the combined effects of physical activity and cold exposure acting synergistically to alter thyroid physiology (e.g., most likely the protein carrier binding affinity).

Training success in U.S. Navy special forces.

Several aspects of success in an intensive military training experience on a select group of military trainees were studied. The primary dependent variables were differences in questionnaire scores between graduates and those who drop, and questionnaire score changes from pretest to posttest in graduates. A total of 336 trainees at the U.S. Navy 's Basic Underwater Demolition/SEALS (BUD/S) training school were tested at the beginning of their training period; 6 months later, all successful trainees were retested on graduation. The total sample was divided into two groups for replication. Results indicated that graduates differed consistently from drops on the Estimation scale of the Physical Estimation and Attraction Scale (PEAS), and four scales on the Hogan Personality Inventory (HPI); graduates showed consistent posttest changes in the Estimation scale, three out of six scales on the Profile of Mood States (POMS), plus four scales on the HPI. Differences between graduates and drops suggested that some aspects of the PEAS and HPI could be used as a screening device in order to reduce attrition. Posttest changes on the PEAS, POMS, and HPI in Graduates were in part consistent with previous work and in part somewhat new, indicating both general and unique features of the BUD/S training experience.

The effects of an augmented and the standard recruit physical training program on fitness parameters.

An investigation was conducted to compare fitness changes elicited by standard Navy recruit physical training with a similar but more intense version of standard training. The sample population included 224 Navy recruits between the ages of 17-30 (means = 19.7 years) participating in 8-week Navy basic training at the Recruit Training Command, San Diego, CA. Subjects were drawn from three recruit companies. Two companies of recruits served as controls and participated in the standard Navy running/calisthenic program. A single experimental company participated in an augmented version of standard training. A battery of fitness measures administered during the initial and final stages of training provided data to contrast training program effects. Study findings indicate that participation in the standard physical training program does not significantly alter the overall fitness level of the average recruit. Participation in the augmented training program provides superior stamina but not muscular strength gains when compared to the standard training format.

Military operations at moderate altitude: effects on physical performance.

The purpose of this study was to examine changes in select anaerobic and aerobic dependent physical performance tasks in U.S. Marines exposured to field operations at moderate altitude. The subjects (N = 16) completed Wingate anaerobic power, submaximal aerobic cycle ergometry, hand grip strength, and push-up tests on three separate occasions. Testing sessions occurred at sea level, at altitude after a 10-day acclimatization period (immediately before field operations), and at altitude immediately after 4.5 days of field operations. Anaerobic power was significantly (p < 0.05) reduced after the field operations at altitude. In contrast, the aerobic cost of doing submaximal exercise was slightly elevated (p < 0.05) after the altitude field operations. No physiologically significant effect was noted for hand grip or push-up results. The findings of this study indicate that field operations at moderate altitude do result in slight, but significant, anaerobic-aerobic performance decrement in U.S. Marines.

Norwegian military field exercises in the arctic: endocrine and metabolic responses.

This study examined select endocrine and metabolic responses of Norwegian soldiers to performing military physical training in an arctic field setting which involved cold exposure. Also, the impact on nocturnal shelter conditions on the physiological responses was investigated. A field based group (EXP, n = 17) lived in tents and a garrison group (CON, n = 16) lived in barracks for 10 days while performing similar daily training in cold weather. Cortisol, testosterone, thyroxine, glucose, triglycerides, and beta-hydroxybutyrate were measured on day 1, 5, and 10 of training. The cortisol and testosterone findings suggest a moderate, but somewhat transient, stress response is associated with field living. The living conditions, however, did not seem to influence the metabolic responses to the physical activity. The observed changes in thyroxine, glucose, and triglycerides (i.e., reductions) suggest that an energy imbalance may accompany military training in the arctic.

Changes in fitness and shipboard task performance following circuit weight training programs featuring continuous or interval running.

Pre- and post-physiological data were collected on 57 Navy men (mean age = 19.5 years) who participated in either circuit weight training/continuous run (CWT/CR) (N = 31) or circuit weight training/interval run (CWT/IR) (N = 26) programs. Measured variables included 4 measures of upper torso dynamic strength (one repetition maximum [1 RM] for arm curl, bench press, shoulder press, and lat pull-down); two measures of lower torso dynamic strength (1 RM) for knee extension and leg press); one measure of power (number of revolutions completed on an arm ergometer (Monark) at maximum drag); three measures of muscular endurance (number of repetitions at 60% 1 RM for bench press and leg press and maximal number of bent-knee sit-ups in 120 s); one stamina measure (time to exhaustion on a cycle ergometer (Monark) maximal work capacity [MWC] test; and three simulated shipboard tasks: manikin shoulder drag, open/secure a water tight door and paint bucket carry. Composite shipboard performance derived from the summed time (s) required to complete the three tasks was also calculated. Results show performance on the manikin shoulder drag and majority of evaluative fitness measures was significantly (p less than 0.05) enhanced following both circuit weight training/run formats. Significantly (p less than 0.05) higher values for shoulder press (F = 7.2), arm ergometer (F = 5.3), and sit-ups (F = 6.8) and lower values for leg press muscular endurance (F = 5.1) were observed in CWT/IR when compared to CWT/CR.(ABSTRACT TRUNCATED AT 250 WORDS)

Thyroid hormone responses to military winter exercises in the Arctic region.

The effects of military field exercises in the arctic on thyroid hormone concentrations were examined in Norwegian soldiers (n = 35). Originally the soldiers were divided into 4 groups having low (2 h) or high (6 h) levels of daily sleep, and low or high physical work requirements during the field exercises. The operations were three days of stimulated combat scenarios during winter. Day 1 consisted of 30 h without sleep. Sleep was then provided at approximately 18-22 h intervals thereafter. Blood samples were taken immediately prior to the exercises (BASELINE), during the exercises at 24 h, 48 h, and 72 h, and at 24 h and 48 h of recovery from the exercises (REC1, and REC2). Hormonal analysis consisted of total (T) thyroxine (TT4), free (f) T4, total triidothyronine (TT3), fT3, and thyroid stimulating hormone (TSH). No significant group interactions were observed therefore groups were pooled. However, main effects over time (i.e., days) were observed for all hormones (p < 0.001). TSH declined throughout the exercises, as did fT3. TT4, fT4, and TT3 increased in the first 24 to 48 h of the exercises, then progressively declined thought REC1. By REC2, TT4, fT4, and TSH showed trends towards returning to BASELINE levels, although recovery was not complete. The findings from this study demonstrates that thyroid hormone concentrations become reduced with as little as 72 h of military field operations in an arctic winter environment. However, short-term sleep deprivation and differing levels of physical work seem to have no major impact on the magnitude of the hormonal changes.

Fitness changes of Naval women following aerobic based programs featuring calisthenic or circuit weight training exercises.

Two research investigations were undertaken to determine the effects of experimental aerobic/circuit weight training (A/CWT) and standard Navy aerobic/calisthenic (A/CAL) training on fitness parameters. Study I Subjects were 22 female officer and enlisted personnel aged 24 to 34 years (mean = 28.2). The women followed a 10-week A/CWT program working at an intensity of 60% of determined one repetition maximum (1RM). These women showed significant (p less than 0.05) improvements in dynamic muscular strength, muscular endurance, and stamina. Only upper torso static strength was unaffected by training. Study II Participants were 115 female recruits aged 17 to 34 years (mean = 20.4). They were randomly assigned to one of three training groups: 1) aerobic/calisthenic training (A/CAL) (N = 58); 2) aerobic/circuit weight training at 40% (A/CWT-40) of maximum strength determined for a single repetition (1RM) of the lifting exercises (N = 26); and 3) aerobic/circuit weight training at 70% (A/CWT-70) of determined 1RM (N = 30). Results showed that standard recruit A/CAL training did not significantly (p less than 0.05) enhance upper torso dynamic strength (except the lat-pulldown test) or stamina. A/CWT-70 elicited significantly (p less than 0.05) higher gains in several tests of upper torso strength than A/CAL or A/CWT-40. These results suggest that A/CWT offers a way to develop the required upper torso strength of Navy women.

Norwegian military field exercises in the arctic: cognitive and physical performance.

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)