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Purpose: Without appropriate standardization of exercise doses, comparing high- (HI) and low-intensity (LI) training outcomes might become a matter of speculation. In athletic preparation, proper quantification ensures an optimized stress-to-recovery ratio. This review aims to compare HI and LI doses by estimating theoretically the conversion ratio, 1:x, between HI and LI: How many minutes, x, of LI are equivalent to 1 minute of HI using various quantification methods? A scrutinized analysis on how the dose increases in relation to duration and intensity was also made. Analysis: An estimation was conducted across 4 categories encompassing 10 different approaches: (1) "arbitrary" methods, (2) physiological and perceptual measurements during exercise, (3) postexercise measurements, and comparison to (4a) acute and (4b) chronic intensity-related maximum dose. The first 2 categories provide the most conservative estimation for the HI:LI ratio (1:1.5–1:10), and the third, slightly higher (1:4–1:11). The category (4a) provides the highest estimation (1:52+) and (4b) suggests 1:10 to 1:20. The exercise dose in the majority of the approaches increase linearly in relation to duration and exponentially in relation to intensity. Conclusions: As dose estimations provide divergent evaluations of the HI:LI ratio, the choice of metric will have a large impact on the research designs, results, and interpretations. Therefore, researchers should familiarize themselves with the foundations and weaknesses of their metrics and justify their choice. Last, the linear relationship between duration and exercise dose is in many cases assumed rather than thoroughly tested, and its use should be subjected to closer scrutiny. [ABSTRACT FROM AUTHOR]

Study aim: Although exercise enjoyment is well studied in behavioral context, its associations to aerobic fitness adaptations during exercise interventions have received less attention.

Background Vitamin D supplementation may lower the risk of acute respiratory infection (ARI), and the effects may be mediated through the induction of cathelicidin production. Objective To study the effect of vitamin D supplementation on ARI and cathelicidin concentration in a randomized controlled trial (RCT) and to study the associations between baseline serum 25 hydroxyvitamin D (25(OH)D) and ARIs and cathelicidin concentrations in a 14-week follow-up study. Methods In the RCT study, the participants were randomized into 2 groups to receive either 20 µg of vitamin D3 or an identical placebo daily. Blood samples were obtained 3 times, at the beginning (study week 0), mid-term (study week 6), and at the end of the study period (study week 14). The follow-up study had 412 voluntary young men from 2 different locations and seasons (January and July). The primary outcomes were the number of ARIs diagnosed and the number of days off because of ARI. Results In the RCT, vitamin D supplementation had no effect on ARI or days off because of ARI. However, regardless of the group, vitamin D insufficiency (<50 nmol/L) was associated with increased ARI. In the 14-week follow-up study, insufficient serum 25(OH)D at baseline was also associated with increased risk of ARI (odds ratio [OR], 2.1; 95% confidence interval [CI], 1.2–3.7) and also days-off duty (OR, 2.3; 95% CI, 1.3–4.0) and was inversely associated with cathelicidin concentration (OR, 0.49; 95% CI,.24–.99). Conclusions Sufficient serum 25(OH)D may be preventive against acute respiratory infection and the preventive effect could be mediated through the induction of cathelicidin production. Clinical Trial Registry number: NCT05014048. https://clinicaltrials.gov/study/NCT05014048?term=NCT05014048&rank=1 [ABSTRACT FROM AUTHOR]

Purpose: Very low intensity endurance training (LIT) does not seem to improve maximal oxygen uptake. The purpose of the present study was to investigate if very high volume of LIT could compensate the lack of intensity and is LIT affecting differently low and high intensity performances. Methods: Recreationally active untrained participants (n = 35; 21 females) cycled either LIT (mean training time 6.7 ± 0.7 h / week at 63% of maximal heart rate, n = 16) or high intensity training (HIT) (1.6 ± 0.2 h /week, n = 19) for 10 weeks. Two categories of variables were measured: Low (first lactate threshold, fat oxidation at low intensity exercise, post-exercise recovery) and high (aerobic capacity, second lactate threshold, sprinting power, maximal stroke volume) intensity performance. Results: Only LIT enhanced pooled low intensity performance (LIT: p = 0.01, ES = 0.49, HIT: p = 0.20, ES = 0.20) and HIT pooled high intensity performance (LIT: p = 0.34, ES = 0.05, HIT: p = 0.007, ES = 0.48). Conclusions: Overall, very low endurance training intensity cannot fully be compensated by high training volume in adaptations to high intensity performance, but it nevertheless improved low intensity performance. Therefore, the intensity threshold for improving low intensity performance is lower than that for improving high intensity performance. Consequently, evaluating the effectiveness of LIT on endurance performance cannot be solely determined by high intensity performance tests. [ABSTRACT FROM AUTHOR]

Purpose: To assess the reliability of nocturnal heart rate (HR) and HR variability (HRV) and to analyze the sensitivity of these markers to maximal endurance exercise. Methods: Recreational runners recorded nocturnal HR and HRV on nights after 2 identical low-intensity training sessions (n = 15) and on nights before and after a 3000-m running test (n = 23). Average HR, the natural logarithm of the root mean square of successive differences (LnRMSSD), and the natural logarithm of the high-frequency power (LnHF) were analyzed from a full night (FULL), a 4-hour (4H) segment starting 30 minutes after going to sleep, and morning value (MOR) based on the endpoint of the linear fit through all 5-minute averages during the night. Differences between the nights were analyzed with a general linear model, and intraclass correlation coefficient (ICC) was used for internight reliability assessments. Results: All indices were similar between the nights followed by low-intensity training sessions. A very high ICC (P <.001) was observed in all analysis segments with a range of.97 to.98 for HR,.92 to.97 for LnRMSSD, and.91 to.96 for LnHF. HR increased (P <.001), whereas LnRMSSD (P <.01) and LnHF (P <.05) decreased after the 3000-m test compared with previous night only in 4H and FULL. Increments in HR (P <.01) and decrements in LnRMSSD (P <.05) were greater in 4H compared with FULL and MOR. Conclusions: Nocturnal HR and HRV indices are highly reliable. Demanding maximal exercise increases HR and decreases HRV most systematically in 4H and FULL segments. [ABSTRACT FROM AUTHOR]

Changes in physiological markers and physical performance in relation to paratroopers' initial body composition were investigated during a 20-day winter military field training (MFT) and the subsequent 10-day recovery period. Body composition, serum hormone concentrations and enzymatic biomarkers, and physical performance of 58 soldiers were measured before, during, and after MFT. Comparisons were done according to soldiers' body fat percentage before MFT between low-fat (<12% body fat) and high-fat (>12% body fat) groups. Correlations between body fat percentage preceding MFT and changes in muscle mass, physical performance, and serum hormone concentrations and enzymatic biomarkers were investigated. It was hypothesized that soldiers with a higher fat percentage would have smaller decrements in muscle mass, physical performance, and serum testosterone concentration. The change in muscle and fat mass was different between groups (p < 0.001) as the low-fat group lost 0.8 kg of muscle mass and 2.0 kg of fat mass, while there was no change in muscle mass and a loss of 3.7 kg of fat mass in the high-fat group during MFT. Fat percentage before MFT correlated with the changes in muscle mass (R2 = 0.26, p < 0.001), serum testosterone concentration (R2 = 0.22, p < 0.001), and evacuation test time (R2 = 0.10, p < 0.05) during MFT. The change in muscle mass was correlated with the changes in evacuation test time (R2 = 0.11, p < 0.05) and countermovement jump test results (R2 = 0.13, p < 0.01) during MFT. Soldiers with a higher initial fat percentage lost less muscle mass, and had smaller decrements in some aspects of physical performance, as well as in serum testosterone concentration during MFT. [ABSTRACT FROM AUTHOR]

BACKGROUND: Military operations in urban environments requires faster movements and therefore may place greater demands on soldier strength and anaerobic ability. OBJECTIVE: The aim was to study how physical fitness and body composition are associated with occupational test for urban combat soldiers before and after a 5-day military field exercise (MFE). METHODS: Twenty-six conscripts (age = 20±1 yrs.) volunteered, of which thirteen completed the study. Occupational performance was determined by using the newly developed Urban Combat Simulation test (UCS); which included 50-m sprinting, moving a truck tire (56 kg) 2 meters with a sledgehammer, a 12-m kettlebell carry (2×20 kg) up the stairs with a 3-m ascent, 4-time sandbag lifts (20 kg) with obstacle crossing, and a 20-m mannequin (85 kg) drag. Aerobic and muscle fitness, as well as anaerobic capacity were measured, and, body composition was assessed with multifrequency bioimpedance analysis. RESULTS: The UCS performance correlated significantly with standing long jump performance, as well as lower and upper body maximal strength before (r = –0.56 to –0.66) and after (r = –0.59 to –0.68) MFE, and, with body mass and FFM before (r = –0.81 to –0.83) and after (r = –0.86 to –0.91) MFE. In the regression analyses, fat free mass (R2 = 0.50, p = 0.01) and counter movement jump in combat load (R2 = 0.46, p = 0.009) most strongly explained the UCS performance. CONCLUSION: This study demonstrated that muscle mass and lower body explosive force production together with maximal strength are key fitness components related to typical urban combat soldiers' military tasks. Physical training developing these components are recommended. [ABSTRACT FROM AUTHOR]

Background: Exercise self-efficacy is a crucial aspect of adopting and maintaining a physically active lifestyle. Regular physical activity may enhance exercise self-efficacy. This study aimed to investigate the baseline associations of physical fitness, physical activity, and body composition with exercise selfefficacy and the effects of military service on exercise self-efficacy. Methods: The sample consisted of healthy young Finnish conscripts (n = 243) undergoing military service. The participants were divided into two groups: an intervention group undergoing a high-intensity functional training program (n = 113) and a control group undergoing traditional physical training within their military service (n = 130). Exercise self-efficacy (adoption and barrier) and aerobic and muscular fitness were measured thrice (baseline, month 3, and month 5). Self-reported leisure-time physical activity and measured fat percentage were collected at baseline. Results: Adoption and barrier exercise self-efficacy correlated positively with aerobic and muscular fitness and leisure time physical activity (r = 0.33–0.59, p < 0.001), and barrier self-efficacy negatively with fat percentage (r = −0.15, p < 0.05) at baseline. No changes in adoption (time p = 0.912) and barrier selfefficacy (time p = 0.441) occurred during the military service. There were no differences between groups in these changes (group × time interaction p = 0.643 for adoption self-efficacy and p = 0.872 for barrier self-efficacy). Change in muscular fitness correlated positively with change in barrier self-efficacy in the high-intensity functional training group (r = 0.35, p < 0.05). Conclusions: Exercise self-efficacy is positively associated with physical fitness and physical activity among young males. However, military service, whether it involves highintensity functional physical training or more diverse traditional physical training, does not improve exercise self-efficacy. [ABSTRACT FROM AUTHOR]

Study aim: The purpose of this study was to evaluate neuromuscular adaptations in conscripts with different fitness levels (VO2max) during 8 weeks of military basic training (BT).

Study aim: The purpose of this study was to compare the effects of cold-water immersion (CWI) vs. active recovery performed after each individual strength and endurance training session over a 10-week period of high-intensity combined strength and endurance training.

Study aim: Physically active adults have been shown to have higher heart rate variability (HRV) than less active adults, but less is known about children in this regard. In adults, training-induced changes in physical performance have been shown to be related to increase in HRV, especially in its high frequency component (HF), which is a marker of parasympathetic activity. The purpose of this study was to examine whether 8 weeks of instructed physical training would improve physical performance and cardiac autonomic function (HRV) in secondary school pupils and to examine the relationship between changes in physical performance and the function of the autonomic nervous system. Material and methods: The test group included 12 girls and 12 boys and the control group 7 girls and 7 boys. All the sub­jects were 13-15 years old. Physical training included warm up, circuit training, endurance training, stretching and relaxation 3 times a week for eight weeks. Endurance training intensity was 70-75% of maximal heart rate. Endurance, flexibility, speed and power were measured before and after training. The low frequency (LF) and high frequency (HF) components of HRV were recorded in supine rest and in standing conditions before and after the eight-week period. Results: Time to exhaustion in the endurance test increased in the test group (p < 0.001), flexibility and ball throwing improved in the test group (p < 0.05), while no changes were observed in the control group. No significant changes were observed in HRV in either group. Conclusions: In conclusion, eight weeks of physical training improves physical performance in children, but it might not affect autonomic cardiac function.

The present study investigated physiological, mental and physical performance changes during a 20-day winter military training course and the following 10-day recovery period. Fifty-eight (age 19 ± 1 years, height 182 ± 6 cm, body mass 78.5 ± 7.2 kg) male soldiers volunteered. Body composition, serum biomarker levels and performance tests were measured four times during the study. In addition, questionnaires were collected daily for subjective stress and rate of perceived exertion. The course induced significant declines in body (−3.9%, p < 0.05) and fat mass (−31.6%, p < 0.05) as well as in all assessed physical performance variables (−9.2 - −20.2%, p < 0.05), testosterone (−73.7%, p < 0.001) and IGF-1 concentrations (−43.6%, p < 0.001). At the same time, the sex hormone-binding globulin, creatine kinase, and C-reactive protein values increased significantly (46.3–1952.7%, p < 0.05). After the 10-day recovery period, the body composition and hormonal values returned to the baseline (p < 0.05), as did some physical performance variables, such as 2 min sit-ups and the evacuation test (p < 0.05). However, explosive force production in the upper and lower bodies remained unrecovered. The 20-day winter military training caused significant physiological and mental stress, as well as a drastic decline in physical performance even for highly physically fit soldiers, and the 10-day recovery period did not establish full recovery. [ABSTRACT FROM AUTHOR]

The present study investigated performance changes during three runs (1 min recovery) of repeated military simulation task test (RMST) and its associations with physical performance. Voluntary male soldiers (N = 114) participated in a series of measurements of physical performance. Lower body explosive force production, anaerobic endurance and upper body strength endurance together explained 58% of the variance in the first RSMT (p < 0.001). The same variables explained the variance in the second and third runs of RSMT by 60% and 51%, but explosive force production was replaced with aerobic endurance, assessed by the 3.2 km loaded run (p < 0.001). This study demonstrated that the role of explosive power of the lower body decreased and military specific aerobic endurance increased when occupational performance was assessed under acute fatigue even during a short high-intensity test. These results may benefit tactical strength and conditioning coaches in training optimisation for improved occupational performance in military. Practioners summary: Soldiers are required to perform occupational tasks in a repeated manner with short recovery time. In the present study, the role of explosive power of the lower body decreased and military specific aerobic endurance increased when occupational performance was assessed with a repeated high-intensity task specific performance test. [ABSTRACT FROM AUTHOR]

Study aim: The aim of this study was to evaluate the possible association of pre-career magnetic resonance imaging (MRI) find­ings and physical performance level with possible musculoskeletal disorders during jet flight training. Material and methods: The study group consisted of 73 fighter pilots who had undergone pre-career cervical and lumbar spine MRI. Physical performance of a subgroup of the pilots (n = 67) was measured initially at the same time and followed up to the fast jet training phase (ranging from 3.8 to 7.0 years). Musculoskeletal pain history during pilot training was taken from the medical charts. MRI findings and physical performance were associated with perceived clinical complaints during the follow-up. Results: 82% of the cervical and 92% of the lumbar spines showed abnormalities at at least one disk level. MRI did not reveal significant cervical degeneration. Thirteen disk bulges in the lumbar spine were discovered, while 5 pilots had listhesis and/or osteophyte formation on the spine (lumbar vertebra 4/sacroiliac joint level, L4-SI). 41% of the studied pilots suffered spinal symptoms during the follow-up, but only 16% and 17% of the cervical and lumbar MRI findings, respectively, were associated with subsequent symptoms. Endurance and strength levels were not, but lower body motor skills were, strongly (relative risk, RR 0.46) associated with a decreased number of flight-induced medical appointments in the early flight career. Conclusions: Minor MRI findings have no predictable value in the very early flight career. Nevertheless, versatile, skills/power-oriented exercises before the flight career seem to be occupationally beneficial in reducing musculoskeletal disorders.

Study aim: To determine the reliability and validity of a time domain heart rate variability (HRV) index during free-living physical activity (FLPA).

Purpose: To determine body composition, energy availability, training load, and menstrual status in young elite endurance running athletes (ATH) over 1 year, and in a secondary analysis, to investigate how these factors differ between nonrunning controls (CON), and amenorrheic (AME) and eumenorrheic (EUM) ATH. Correlations to injury, illness, and performance were also examined. Methods: Altogether 13 ATH and 8 CON completed the Low Energy Availability in Females Questionnaire. Anthropometric, energy intake, and peak oxygen uptake assessments were made at 4 time points throughout the year: at baseline post competition season, post general preparation, post specific preparation, and post competition season the following year. Logs of physical activity, menstrual cycle, illness, and injury were kept by all participants. Performance was defined using the highest International Association of Athletics Federations points prior to and after the study. Results: ATH had significantly lower body mass (P <.008), fat percentage (P <.001), and body mass index (P <.027) compared with CON, while energy availability did not differ between ATH and CON. The Low Energy Availability in Females Questionnaire score was higher in ATH than in CON (P <.028), and 8 ATH (vs zero CON) were AME. The AME had significantly more injury days (P <.041) and ran less (P <.046) than EUM, while total annual running distance was positively related to changes in performance in ATH (r <.62, P <.043, n < 11). Conclusions: More than half of this group of runners was AME, and they were injured more and ran less than their EUM counterparts. Furthermore, only the EUM runners increased their performance over the course of the year. [ABSTRACT FROM AUTHOR]