Effects of a 10-d Military Field Exercise on Body Composition, Physical Performance, and Muscle Cells in Men and Women

PURPOSE

This study aimed to investigate the effects of a demanding military field exercise on physical performance, body composition, and muscle cellular outcomes in men and women.

METHODS

Ten men (20.5 ± 0.5 yr) and 8 women (21.4 ± 1.4 yr) completed a 10-d field exercise consisting of extensive physical activity with food and sleep restriction. Acquisition of body composition, physical performance, blood, and muscle biopsies samples were done before and 1, 7, and 14 d after the exercise.

RESULTS

There were no sex differences in the response to the exercise. Body mass was decreased with 5.6% ± 1.8% and fat mass with 31% ± 11% during the exercise. Both were still reduced after 14 d (2.5% ± 2.3%, P < 0.001, and 12.5% ± 7.7%, P < 0.001, respectively). Isometric leg strength did not change. Peak leg extension torque at 240°·s -1 and counter movement jump height were reduced with 4.6% ± 4.8% ( P = 0.012) and 6.7% ± 6.2% ( P < 0.001), respectively, and was still reduced after 14 d (4.3% ± 4.2%, P = 0.002, and 4.1% ± 4.7%, P = 0.030). No changes occurred in fiber CSA, fiber types, proteins involved in calcium handling, or HSP70. During the exercise, αB-crystallin levels decreased by 14% ± 19% ( P = 0.024) in the cytosolic fraction and staining intensity on muscle sections tended to increase (17% ± 25%, P = 0.076). MuRF1 levels in the cytosolic fraction tended to decrease (19% ± 35%) and increased with 85% ± 105% ( P = 0.003) in the cytoskeletal fraction 1 wk after the exercise.

CONCLUSIONS

The field exercise resulted in reduced body mass and physical performance in both sexes. The ability to produce force at high contraction velocities and explosive strength was more affected than isometric strength, but this was not related to any changes in fiber type composition, fiber area, Ca 2+ handling, or fiber type-specific muscle damage.

Relationship between self-reported and objectively measured physical fitness in young men and women

Self-reported physical fitness has advantages in cost and time over objective methods, but previous studies demonstrate equivocal conclusions regarding validity. Methods for self-reporting are usually based on subjective judgements, while another approach includes performing field tests at home. The Norwegian military relies on the latter method for conscript selection, but its validity is unknown and should be investigated. In total 14,166 young men and women were included in the study. During conscript selection step one, the subjects were requested to perform 3,000 m run, push-up, pull-up and standing long jump tests at home, and report the results online ("self-reported measurements"). Step two took place at a conscript selection centre 1-18 months later. Here, the subjects completed a maximal treadmill test, seated medicine ball throw, pull-up and standing long jump tests ("objective measurements"). The results demonstrated correlation coefficients from 0.29 to 0.82 (P < 0.05) for self-reported vs. objective measurements, with the highest association found for self-reported and objectively measured pull-ups. Kappa values ranged from 0.05 to 0.34 (P < 0.05), with pull-ups demonstrating the highest agreement. More women than men over-reported their physical fitness. Among men and women indicating similar self-reported fitness, men's objective fitness was higher for all objective tests (effect sizes from 0.5 to 3.0). In conclusion, large variations in correlation coefficients were observed between self-reported and objectively measured physical fitness, while the kappa values indicated poor to fair agreement. The finding that more women than men over-reported their fitness level contradicts most previous studies.Highlights Low, moderate, and high correlations, and poor to fair agreements (kappa values), were observed between self-reported and objectively measured endurance and muscle strength variables.More women than men overreported their actual fitness level.Self-reported fitness based on performing field tests at home may be a feasible alternative to traditional methods which rely on self-perceived fitness.

Temporal changes in physical fitness in Norwegian male and female military conscripts between 2006 and 2020

Reduced physical fitness has been documented in Western children and adults over the past five decades. The same trend has been observed among soldiers, but the number of studies is scarce. Thus, the aim of the present study was to investigate temporal changes in physical fitness in Norwegian conscripts. All conscripts who performed entry fitness tests between 2006 and 2020 were included in the study (n = 105 100; 17% females). Endurance was measured with the 3000 m run, while push-ups, sit-ups, and pull-ups (2006-2016) and medicine ball throw, standing long jump, and pull-ups (2017-2020) were used to measure muscle strength. Mean (95% confidence intervals) 3000 m run time was reduced by 52 (47, 57) seconds in men, 90 (76, 105) seconds in women, and 16 (11, 20) seconds in both sexes combined. Muscle strength increased statistically significantly in four out of five tests in men, three out of six tests in women, and two out of five tests for both sexes combined. Effect sizes for statistically significant changes ranged from 0.06 to 0.82. In conclusion, Norwegian conscripts improved their cardiorespiratory endurance between 2006 and 2020, with improvements observed for most muscle strength tests. When analyzing both sexes combined, the improvements diminished. The latter is attributed to a sevenfold increase in relative number of female conscripts over the 15-year period. The present findings should not be generalized to all young Norwegian men and women since conscripts are selected based on fitness, and only ~15% of the population end up serving.

Self-Perceived and Self-Tested Endurance: Associations with Objective Measures

Use of self-report (questionnaires) is often the most realistic means of screening physical fitness in large participant samples because this method is quicker and cheaper than objective testing. Yet, previous studies have reported equivocal validity to reports of self-perceived fitness. A hybrid self-report variant is the use of self-administered/reported objective measurement. We sought to investigate the relative validity of this variant method compared to self-perception reports. In total 26,452 young Norwegian men and women participated in this study. We collected data during obligatory selection for military conscript service. Approximately half of the participants were asked to rate their endurance level on a five-point Likert scale in an online questionnaire. The other half performed a self-administered 3000 m run and reported the result online. Within 18 months, all participants completed an objective maximal treadmill test at a conscript selection center. We used Spearman correlations (r_s) and analyses of variance (ANOVAs) to investigate the relationships between these two self-report methods and the observed objective treadmill performance. Self-perceived and self-tested endurance were both identically correlated with the other-observed treadmill run for men (r_s = 0.59; p < .001) and for women (r_s = 0.50, p < .001); and ANOVAs revealed significant effects of self-perceived and self-tested endurance on treadmill run time, with higher self-reported endurance related to higher treadmill run time. In conclusion, self-perceived and self-tested endurance produced the same correlation coefficients with objectively measured treadmill run time. While there was a moderate relationship between self-reported and objectively measured endurance at the group level, there was substantial individual measurement error that should be considered for individual reports.

Reference data on anthropometrics, aerobic fitness and muscle strength in young Norwegian men and women

Purpose

Anthropometrics, aerobic fitness and muscle strength are measured in one-third of all 18-year-old Norwegian men and women during yearly selection for compulsory military service. The large sample size and geographical representativity make these data valuable for reference. The main purpose of this study was to present reference data for anthropometrics and physical fitness in young Norwegian men and women.

Methods

All 154,659 subjects (66% men and 34% women, 17–21 years old) who completed physical examinations at conscript selection from 2011 to 2019 were included in the study. Body mass index (BMI) was calculated from height and weight measurements. Peak oxygen uptake (VO_2peak) was estimated from performance on a maximal treadmill test. Muscle strength was measured by isometric chest and leg press, or seated medicine ball throw, standing long jump and pull-ups.

Results

Mean BMI (SD) was 23.1 (3.4) and 22.9 (3.3) kg·m⁻² in men and women, respectively (P < 0.001), and 24% of men and 21% of women had a BMI ≥ 25 kg·m⁻². Estimated VO_2peak was 52.9 (4.6) and 42.7 (3.9) mL·kg⁻¹·min⁻¹ in men and women, respectively (P < 0.001). Men performed significantly better than women on all muscle strength tests, with corresponding effect sizes varying from 1.14 for isometric leg press to 2.96 for seated medicine ball throw.

Conclusion

The presented reference data on physical fitness in young Norwegian men and women can be used to evaluate population health, serve as reference material for future studies and describes sex differences in several physical fitness parameters.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-021-04784-4.

Estimation of maximal oxygen uptake from the 3,000 m run in adult men and women

The 3,000 m run is a frequently used field test for evaluating aerobic fitness. The test has previously been validated using smaller sample sizes and with focus restricted to the correlation between run performance and maximal oxygen uptake (V̇O_2max). The aim of the present study was to generate equations for converting 3,000 m performance into predicted V̇O_2max , and present corresponding validity statistics. In total 259 (30 female) military cadets and recruits (18-39 years) participated in the study. The subjects carried out a 3,000 m run and a direct treadmill V̇O_2max test. The Pearson r between V̇O_2max and average 3,000 m run speed were 0.74 and 0.79 in men and women, respectively. Two V̇O_2max prediction equations were generated: (1) Men: Ŷ = 17.5 + 2.57X and (2) Women: Ŷ = 14.6 + 2.48X (X = 3,000 m average run speed in km·h^-1). The equations produced a standard error of estimate of 3.3 and 2.6 mL·kg^-1·min^-1, and limits of agreement of 6.4 and 5.0 mL·kg^-1·min^-1 in men and women, respectively. The validity of the 3,000 m test is comparable to other indirect maximal running tests and is a time-effective alternative aerobic fitness test in healthy and motivated subjects.

Change in Anthropometrics and Physical Fitness in Norwegian Cadets During 3 Years of Military Academy Education

INTRODUCTION

High physical fitness is associated with increased occupational performance, better health, and reduced risk of injuries in military personnel. Thus, the military emphasizes physical training to maintain or develop physical fitness in their soldiers. It is important to monitor the effect of the physical training regime, but such information is lacking for Norwegian military cadets. Hence, the primary aim of this study was to investigate changes in anthropometrics and physical fitness among male and female army, navy and air force cadets during 3 years of military academy education.

MATERIALS AND METHODS

260 male and 29 female Norwegian cadets from the army, navy, and air force academies volunteered to participate. Anthropometrics, muscular power, muscular endurance, and maximal oxygen uptake were measured at entry (T0) and end of each year (T1, T2, and T3). Linear mixed models were used to examine the development in anthropometrics and physical fitness. We applied to the Regional Committee for Medical and Health Research Ethics to review the study before start-up, but the study was considered exempted from notification. The study was reviewed and approved by the Norwegian Social Science Data Services.

RESULTS

Male and female cadets significantly increased their body weight, fat-free mass, body mass index, and percent body fat by 1 to 5% from T0 to T3. Skeletal muscle mass was unchanged. Muscular power (medicine ball throw and vertical jump) and muscular endurance (pull-ups and push-ups) increased by 3 to 20% in male cadets, while female cadets only increased results significantly for the medicine ball throw (10%). Relative maximal oxygen uptake decreased by 4% in both sexes, while absolute maximal oxygen uptake only decreased significantly (by 2%) in male cadets. Most of the observed changes were classified as trivial or small, according to calculated effect sizes. The observed changes were generally of similar magnitude for male and female cadets, and similar among the three academies.

CONCLUSIONS

Anthropometrics and physical fitness were relatively stable in Norwegian male and female army, navy, and air force cadets during 3 years of military academy education. Observed changes were typically classified as trivial or small. The initial gap in physical fitness between male and female cadets did not narrow during the education years. Norwegian male and female cadets displayed relatively good physical fitness profiles, compared to sex-matched cadets and soldiers from previously studied military populations.

Association Between Performance in Muscle Fitness Field Tests and Skeletal Muscle Mass in Soldiers

INTRODUCTION

Muscle strength and muscle endurance are important fitness components related to safe and efficient execution of physically demanding military work. In soldiers, these components are traditionally measured from simple field tests like push-ups, sit-ups, and pull-ups. However, the validity of such muscle fitness field tests is questioned due to reports of low association between test performance and the ability to conduct strength demanding military work (eg, lift and carry tasks). It is therefore necessary to study, develop, and implement more valid field tests, which are still feasible for mass testing in the military. Skeletal muscle mass (SMM) is an important physiological component related to maximal muscle force generation (strength). Thus, an alternative way of validating muscle fitness field tests is by comparisons against SMM. The purpose of the present study was to investigate the association between SMM and performance in five muscle fitness field tests.

MATERIALS AND METHODS

A total of 275 military cadets (including 27 women) participated in this method comparison study. The field tests included push-ups, sit-ups, pull-ups (vertical for men, horizontal for women), standing medicine ball throw, and Sargent jump (peak power and jump height). SMM was estimated from bioelectrical impedance analysis and expressed in absolute values (kg) or relative to body mass. Pearson correlation coefficients (r) were calculated to investigate associations between SMM and performance in the five field tests. The study was submitted to the Regional Committee for Medical and Health Research Ethics prior to startup, and the Committee considered the study to be exempted from notification. The study was reviewed and approved by the Norwegian Social Science Data Services.

RESULTS

In men, the highest correlation against absolute SMM was found for the Sargent jump (peak power) and the medicine ball throw (r = 0.71 and 0.54, respectively). The same trend was evident for women (r = 0.85 and 0.61, respectively) and for the two genders combined (r = 0.85 and 0.79, respectively). All these r-values were significant (P < 0.001). In men, the highest r against relative SMM was found for pull-ups (r = 0.50, P < 0.001). The same pattern was found in women, but the association was not significant (r = 0.36, P = 0.07). The sit-ups test demonstrated low or nonsignificant associations with both absolute and relative SMM.

CONCLUSIONS

Among the five muscle fitness field tests investigated, the Sargent jump (peak power) and the medicine ball throw demonstrated the strongest correlation coefficients against absolute SMM. Thus, these two tests should be better alternatives for assessing relevant upper and lower body strength and power in soldiers compared with push-ups, pull-ups, and sit-ups. Pull-ups generally demonstrated the strongest correlation against relative SMM. Sit-ups demonstrated low or nonsignificant associations with both absolute and relative SMM. Consequently, the test should be considered for removal from military fitness test batteries or replaced by alternative abdominal tests that are more valid.

Reliability and Validity of a Maximal Treadmill Test for Predicting Aerobic Fitness in Norwegian Prospective Soldiers

INTRODUCTION

The Norwegian armed forces reintroduced physical fitness testing of prospective conscript soldiers in 2011. Since then, a customized maximal treadmill test (MILMAX) has been used to screen aerobic fitness in 15-20,000 young Norwegian men and women annually. The aim of the current study was to investigate reliability and validity of the MILMAX test.

MATERIALS AND METHODS

Sixty-seven young Army recruits (including 11 women) participated in this method comparison study. The subjects completed the MILMAX test twice (test-retest), consisting of walking and running at increasing speed and inclination until voluntarily exhaustion. Performance was registered as exercise tolerance time (ETT). Later, the subjects performed a treadmill test of direct maximal oxygen uptake (V̇O2max). All tests were conducted within 15 days. The study protocol was submitted to the Regional Committee for Medical and Health Research Ethics for review, prior to study initiation. The Committee considered the study to be exempted from notification. The study was carried out according to the guidelines in the Declaration of Helsinki.

RESULTS

There was no significant mean difference in MILMAX ETT between test and retest. Test-retest intraclass correlation coefficient was 0.95 (0.91, 0.97), while 95% limits of agreement was ± 60 seconds. Regression analyses showed that MILMAX ETT and gender explained 78% of the variance in directly measured V̇O2max, and a prediction equation with these two independent variables was generated. The Pearson correlation coefficient between predicted and directly measured V̇O2max was 0.89 (0.83, 0.93), while limits of agreement was ± 5.6 mL·kg-1·min-1.

CONCLUSIONS

The MILMAX is equally reliable and valid compared with well-known maximal indirect tests like the 2-mile run and the 20-m shuttle run test, and may serve as an alternative indoor test of aerobic fitness in the military, in other potentially physically strenuous occupations, or in healthy civilians.

Exploring the interplay between the motivational climate and goal orientation in predicting maximal oxygen uptake

Drawing upon achievement goal theory, this study explored the interplay between the perceived motivational climate, achievement goals and objective measurements of maximal oxygen uptake (VO2max). The results of a study of 123 individuals from three Norwegian military academies revealed that under the condition of a high-performance orientation there is a stronger positive relationship between performance climate and VO2max for individuals reporting a low (rather than high)-mastery orientation. Furthermore, we found that for individuals with a high-mastery orientation there is a stronger positive relationship between mastery climate and VO2max for individuals reporting a low (rather than high)-performance orientation. These findings contribute to achievement goal theory by providing support for an interactionist person-environment fit perspective. Implications for future research and practice are discussed.

Reliability and validity of the soccer specific INTER field test

The aims of this study were to explain how the Intermittent Endurance Running (INTER) test is executed, describe physiological responses during testing, and evaluate reliability and content validity in this new soccer specific test. The test consists of 20 m shuttle running, interspersed with straight sprints, agility sprints, walking and resting. Shuttle run speed is increased at each level until exhaustion. Thirteen male professional players participated in the present study. Exercise tolerance time, distance covered, mean blood lactate and mean heart rate were 25:51 ± 2:41 min, 2892 ± 324 m, 5.5 ± 1.2 mmol · L(-1) and 161 ± 11 beats · min(-1), respectively, during the INTER test. Sprint and agility performance decreased significantly at higher levels. Eight of the players performed a retest for reliability evaluations. Mean difference ± 95% limits of agreement, coefficient of variation (CV) and intraclass correlation coefficient (ICC) for exercise tolerance time between test and retest were -00:41 ± 02:25 min, 2.5% and 0.75, respectively. The CV for sprint and agility performance between test and retest was <1%. The INTER test mimics soccer games on distance/time ratio, frequency of sprints, heart rate and blood lactate values, and could be an alternative field test for evaluating essential physical performance aspects in soccer players.

Change in anthropometrics and aerobic fitness in Air Force cadets during 3 years of academy studies

INTRODUCTION

Favorable anthropometrical status and aerobic fitness levels are emphasized in Norwegian Air Force personnel. However, it is unknown how these variables develop in Air Force cadets. Thus, the main aim of the present study was to examine how anthropometrics and maximal oxygen uptake (VO2(max)) change among Norwegian Air Force cadets during 3 yr of Academy studies.

METHODS

There were 30 male cadets included in the study. Bodyweight, body mass index (BMI), estimated percent body fat, and VO2(max) were measured at entry and at the end of the first year of Academy studies. After the first year, 14 cadets left the Academy, while the remaining cadets were retested at the end of the second and third years. RESULTS63: At entry, mean (95% CI) bodyweight, BMI, percent body fat, and VO2(max) were 78.4 (75.2, 81.6) kg, 24.3 (23.5, 25.1) kg x m(-2), 17.8 (16.3, 19.3)%, and 4.48 (4.25, 4.72) L x min(-1), respectively. Percent body fat decreased significantly by 1.1 (0.2, 2.0) percentage points at the end of the first year, while the other variables did not change during the first year. Between entry and end of third year there was no change in any of the main outcome variables.

DISCUSSION

Anthropometrical status and VO2(max) did not change in Norwegian Air Force cadets between entry and the end of 3 yr of Air Force Academy studies. From the 1- and 3-yr follow-up analysis, the only significant change was a small reduction in estimated percent body fat from entry to the end of the first year.

Validity and reliability of the 20 meter shuttle run test in military personnel

is regularly monitored in military personnel, as occupational demands require a certain level of fitness. Distance run (eg, 2 mile) is typically carried out to measure aerobic fitness, but an alternative test could be the 20 meter shuttle run test (20 m SRT). The present study aimed to evaluate validity and reliability of this test in military personnel. An equation for predicting maximal oxygen uptake (VO2max) was developed on 38 Home Guard soldiers and cross validated in 28 Air Force cadets. Reliability of the 20 m SRT, expressed as mean difference in estimated VO2max-- 95% limits of agreement, was -0.8 +/- 3.1 mL x kg(-1) min(-1). Mean difference +/- limits of agreement between estimated and measured VO2max was -0.4 +/- 6.2 mL.kg(-1)x min-'. The 20 m SRT seems to be a reliable test, although validity is less certain, as relatively high variability was observed between measured and estimated VO2max from the 20 m SRT.

Asthma symptoms in rural living Tanzanian children; prevalence and the relation to aerobic fitness and body fat

OBJECTIVE

To determine the prevalence of asthma symptoms in children from a rural district in North-Tanzania, and their relationship to aerobic fitness and body fat.

METHODS

In Manyara region in Tanzania, children (aged 9-10 years) were randomly selected to participate in the present cross-sectional study. Hundred and seventy two participants completed a video questionnaire showing the symptoms and signs of asthma. Lung function was measured by maximum forced expiratory flow-volume curves. Aerobic fitness was estimated from a standardized indirect maximal cycle ergometer test and sum of three skinfolds reflected body fat.

RESULTS

Twenty four per cent reported asthma symptoms last year. Severe wheezing attacks last year were reported in 5% of the participants. Thirty seven per cent of the participants were underweight. Underweight children had significantly lower (P < 0.02) lung function (per cent of predicted). Lower body fat was associated with higher occurrence of asthma symptoms (odds ratio and 95% CI; 0.45 (0.22-0.95; P = 0.04). Aerobic fitness was not associated with asthma symptoms.

CONCLUSIONS

More than every fifth 9-10 year old child from a rural district in North-Tanzania reported asthma symptoms. Lower body fat was associated with higher occurrence of asthma symptoms, but aerobic fitness was not associated with asthma symptoms.

A comparison of estimated maximal oxygen uptake in 9 and 10 year old schoolchildren in Tanzania and Norway

OBJECTIVE

To compare estimated maximal oxygen uptake (VO2max) in Tanzanian and Norwegian children, by using the same bicycle protocol in both samples.

METHODS

Maximal oxygen uptake was estimated from an indirect maximal watt cycle ergometer test in 156 rural boys and girls in Tanzania. Similarly aged urban Norwegian boys and girls (n = 379) who underwent the same test were used for comparison. The Tanzanian children also participated in a 20 metre shuttle run test and a test of bicycle skill. The Tanzanian children were tested at altitude (approximately 1800 metres), while the Norwegian children were tested at sea level.

RESULTS

In the cycle ergometer test, estimated relative VO2max was similar in Tanzanian and Norwegian boys, while Tanzanian girls had 8% lower estimated VO2max compared with Norwegian girls (p<0.001). Only one third of the Tanzanian children were able to ride a conventional bicycle. Excluding subjects not able to ride a bicycle, there was no difference in estimated VO2max between Norwegian and Tanzanian children. The Tanzanian boys and girls reached significantly higher estimated VO2max in the shuttle run test compared with the cycle ergometer test (p<0.001).

CONCLUSIONS

Tanzanian and Norwegian children attained similar relative VO2max in the cycle ergometer test. However, the comparison was hampered by differences in altitude and the poor cycle ergometer skills in the Tanzanian children, both of which probably underestimated their VO2max.

Aerobic fitness in young Norwegian men: a comparison between 1980 and 2002

The purpose of this study was to compare the maximal oxygen uptake (VO2max) in 18-19-year-old Norwegian men from 1980 to 1985 and 2002. In addition, we investigated the relationship between VO2max and education and smoking habits in the sample from 2002. From 1980 to 1985, VO2max was predicted using the Astrand-Rhyming bicycle test for 183 610 eighteen-year-old Norwegian men (91% of the male Norwegian population in this age group). In 2002, the same test was performed on a representative sample of the same age population (N=1028). VO2max (mL x kg(-1)x min(-1)), decreased by 8%, body weight increased by 7% and body mass index (BMI) increased by 6% over the approximately 20-year period (P<0.01). Results from the 2002 sample revealed that smokers had a lower VO2max than non-smokers and vocational students had a lower VO2max than academic students (P<0.05). The average reduction in VO2max was because of an increased number of men with low or very low VO2max, and a reduced number of men with high VO2max values. This is of particular concern since the prevalence of lifestyle-related diseases is higher in groups with low VO2max.