Water immersion methods do not alter muscle damage and inflammation biomarkers after high-intensity sprinting and jumping exercise.

PURPOSE: The aim of this study was to compare the efficacy of three water immersion interventions performed after active recovery compared to active recovery only on the resolution of inflammation and markers of muscle damage post-exercise. METHODS: Nine physically active men (n = 9; age 20‒35 years) performed an intensive loading protocol, including maximal jumps and sprinting on four occasions. After each trial, one of three recovery interventions (10 min duration) was used in a random order: cold-water immersion (CWI, 10 °C), thermoneutral water immersion (TWI, 24 °C), contrast water therapy (CWT, alternately 10 °C and 38 °C). All of these methods were performed after an active recovery (10 min bicycle ergometer), and were compared to active recovery only (ACT). 5 min, 1, 24, 48, and 96 h after exercise bouts, immune response and recovery were assessed through leukocyte subsets, monocyte chemoattractant protein-1, myoglobin and high-sensitivity C-reactive protein concentrations. RESULTS: Significant changes in all blood markers occurred at post-loading (p < 0.05), but there were no significant differences observed in the recovery between methods. However, retrospective analysis revealed significant trial-order effects for myoglobin and neutrophils (p < 0.01). Only lymphocytes displayed satisfactory reliability in the exercise response, with intraclass correlation coefficient > 0.5. CONCLUSIONS: The recovery methods did not affect the resolution of inflammatory and immune responses after high-intensity sprinting and jumping exercise. It is notable that the biomarker responses were variable within individuals. Thus, the lack of differences between recovery methods may have been influenced by the reliability of exercise-induced biomarker responses.

Functional test measures as risk indicators for low back pain among fixed-wing military pilots.

PURPOSE: The purpose of this study was to find out the risk value of functional fitness test (FFT) results for low back pain (LBP) among fixed-wing military pilots. METHODS: A total of 104 male military pilots were recruited for this study. The study was conducted with a self-administered questionnaire and FFT. The functional tests were performed in the beginning of study (baseline). The questionnaire was carried out at the baseline and 5 years later. RESULTS: The isometric low back endurance test result was associated with physical activity-related LBP experienced 5 years later. Demographic information was not associated with LBP. The prevalence of overall LBP was 71% and the flight-related LBP prevalence was 31% at the baseline. DISCUSSION: Our findings show that LBP among military pilots is a common problem but it is also associated with tasks other than flying. The functional test results were not associated with flight-related LBP but adequate isometric back endurance may have protective role in LBP caused in physical activities. When trying to find the pilots with increased risk of flight-related LBP, a more sensitive set of tests should be considered.

Greater levels of cardiorespiratory and muscular fitness are associated with low stress and high mental resources in normal but not overweight men.

BACKGROUND: The aim of the present study was to investigate how cardio respiratory (CRF) and muscular fitness (MF) together with leisure-time physical activity (LTPA) influence stress symptoms and mental resources among normal-weight and overweight men, because it is not known how body weight affects this association. METHODS: In a cross-sectional study, 824 men (mean ± SD: age 25 ± 5 y, weight 81 ± 13 kg, BMI 25 ± 4 kg/m(2)) underwent CRF and MF tests and completed LTPA and stress questionnaires. For the analysis, the subjects were divided into BMI groups (normal vs. overweight) and CRF / MF / LTPA (low, moderate, high) tertiles. RESULTS: Normal-weight men with low CRF reported 12 % (p = 0.001) more stress symptoms (SS) compared to normal-weight men with moderate CRF, and 13 % (p = 0.004) more SS compared to normal-weight men with high CRF. Normal-weight men with low MF reported 13 % (p = 0.001) higher SS compared to normal-weight men with moderate MF and 16 % (p = 0.002) more SS compared to men with high MF. Among overweight men, there were no significant differences in SS or mental resources (MR) between the low, moderate and high CRF and MF tertiles. Overweight men with high CRF experienced 8 % (p = 0.039) more SS compared to normal-weight participants with high CRF when age, tobacco and alcohol use, MF and LTPA were considered as covariates (p = 0.014). CONCLUSION: Higher CRF and MF are associated with lower stress and higher mental resources in normal-weight men, but in overweight men, these relationships may differ.

Maximal strength, muscular endurance and inflammatory biomarkers in young adult men.

The aim was to study associations of maximal strength and muscular endurance with inflammatory biomarkers independent of cardiorespiratory fitness in those with and without abdominal obesity. 686 young healthy men participated (25±5 years). Maximal strength was measured via isometric testing using dynamo-meters to determine maximal strength index. Muscular endurance index consisted of push-ups, sit-ups and repeated squats. An indirect cycle ergometer test until exhaustion was used to estimate maximal aerobic capacity (VO2max). Participants were stratified according to those with (>102 cm) and those without abdominal obesity (<102 cm) based on waist circumference. Inflammatory factors (C-reactive protein, interleukin-6 and tumour necrosis factor alpha) were analysed from serum samples. Maximal strength and muscular endurance were inversely associated with IL-6 in those with (ß=-0.49, -0.39, respectively) (p<0.05) and in those without abdominal obesity (ß=-0.08, -0.14, respectively) (p<0.05) adjusted for smoking and cardio-respiratory fitness. After adjusting for smoking and cardiorespiratory fitness, maximal strength and muscular endurance were inversely associated with CRP only in those without abdominal obesity (ß=-0.11, -0.26, respectively) (p<0.05). This cross-sectional study demonstrated that muscular fitness is inversely associated with C-reactive protein and IL-6 concentrations in young adult men independent of cardiorespi-ratory fitness.

Associations of maximal strength and muscular endurance with cardiovascular risk factors.

The aim was to study the associations of maximal strength and muscular endurance with single and clustered cardiovascular risk factors. Muscular endurance, maximal strength, cardiorespiratory fitness and waist circumference were measured in 686 young men (25±5 years). Cardiovascular risk factors (plasma glucose, serum high- and low-density lipoprotein cholesterol, triglycerides, blood pressure) were determined. The risk factors were transformed to z-scores and the mean of values formed clustered cardiovascular risk factor. Muscular endurance was inversely associated with triglycerides, s-LDL-cholesterol, glucose and blood pressure (ß=-0.09 to - 0.23, p<0.05), and positively with s-HDL cholesterol (ß=0.17, p<0.001) independent of cardiorespiratory fitness. Muscular endurance was negatively associated with the clustered cardiovascular risk factor independent of cardiorespiratory fitness (ß=-0.26, p<0.05), whereas maximal strength was not associated with any of the cardiovascular risk factors or the clustered cardiovascular risk factor independent of cardiorespiratory fitness. Furthermore, cardiorespiratory fitness was inversely associated with triglycerides, s-LDL-cholesterol and the clustered cardiovascular risk factor (ß=-0.14 to - 0.24, p<0.005), as well as positively with s-HDL cholesterol (ß=0.11, p<0.05) independent of muscular fitness. This cross-sectional study demonstrated that in young men muscular endurance and cardiorespiratory fitness were independently associated with the clustering of cardiovascular risk factors, whereas maximal strength was not.

Physical fitness and volume of leisure time physical activity relate with low stress and high mental resources in young men.

AIM: There is limited evidence available regarding the relationship between physical fitness, especially muscular fitness, and the mental well-being among young healthy men. Therefore, the aim of the present study was to investigate the impact of measured cardiovascular and muscle fitness and self reported leisure time physical activity (LTPA) on outcomes of stress and mental resources in Finnish young men. METHODS: In a cross-sectional study, 831 men (mean age 25 y) underwent cardiovascular and muscle fitness test and completed LTPA and Occupational Stress Questionnaires (OSQ). For analysis, the subjects were divided to LTPA, CVF and MFI tertiles. RESULTS: The group with low LTPA reported 6% and 13% more stress (ANCOVA using age, body mass index, smoking and alcohol use as covariates, P<0.05 in both) and 6% and 12% (P<0.05 in both) less mental resources than the moderate and high LTPA groups, respectively. The group having low cardiovascular fitness experienced 8% and 9% (P<0.001 in both) more stress and 7% and 7% (P<0.05 in both) less mental resources than moderate and high cardiovascular fitness groups. The low muscle fitness index (MFI) group reported 7% (P<0.01) less mental resources than those with moderate MFI and 8% (P<0.001) more stress and 8% (P<0.001) less mental resources than those with high MFI. CONCLUSION: Both good aerobic and muscular fitness together with high LTPA are associated with low stress and high mental resources.

Physical activity, physical fitness and cardiometabolic health among Finnish military workers.

INTRODUCTION: The Western lifestyle challenges national defence. Inactivity, obesity, high BP and elevated lipid and glucose levels as well as tobacco use all increase cardiometabolic risk. The present study was thus aimed at investigating the health and physical activity of employees in a military environment, concentrating on comparisons between soldiers and civilians. METHODS AND DESIGN: A total of 260 employees from 6 brigades were included in the present study. Health status was evaluated with body composition, cardiometabolic risk markers from laboratory samples and a questionnaire concerning lifestyle habits. Body composition was assessed by means of body mass, body mass index, fat percentage and waist circumference. Furthermore, physical activity was examined by the aid of accelerometer recordings for a 2-week period, and physical fitness via aerobic and muscle fitness tests. Finally, upper-quartile active and lower-quartile passive participants were compared, by incorporating mean daily step counts. RESULTS: When standardised by gender, there were no differences between the soldiers and civilians except for the muscle fitness test, in which soldiers performed better. The mean (±SD) moderate to vigorous activity was 0.9±0.3 hours/day in male soldiers and 1.0±0.4 hours/day in male civilians, and respectively sedentary behaviour was 9.5±1.4 hours/day in male soldiers and 8.9±1.7 hours/day in male civilians. The mean (±SD) low-density lipoprotein values were 3.28±0.84 mmol/L in male soldiers and 3.36±0.86 mmol/L in male civilians. In comparing soldiers and civilians, statistically significant differences were observed in body composition, physical fitness, insulin, fasting glucose, triglycerides and high-density lipoprotein values between the upper-quartile active and lower-quartile passive participants, but no difference in low-density lipoprotein values was noticed. CONCLUSIONS: Sedentary behaviour and elevated low-density lipoprotein values seem to increase cardiometabolic disease risk among participants, even if they meet the weekly physical activity demands.

Regional differences in blood flow, glucose uptake and fatty acid uptake within quadriceps femoris muscle during dynamic knee-extension exercise.

The purpose of the present study was to investigate the regional differences in glucose and fatty acid uptake within skeletal muscle during exercise. Blood flow (BF), glucose uptake (GU) and free fatty acid uptake (FFAU) were measured in four different regions (vastus lateralis, VL; rectus femoris, RF; vastus intermedius, VI; and vastus medialis, VM) of the quadriceps femoris (QF) muscle during low-intensity, knee-extension exercise using positron emission tomography. BF was higher in VI than in VL, RF and VM (P < 0.05). FFAU was higher in VI (P < 0.001) but also in VM (P < 0.05) compared with VL and RF. In contrast, GU was higher in RF compared with VL (P < 0.05) but was not significantly different to VM or VI (both P = NS). FFAU within these four muscle regions correlated significantly with BF (r = 0.951, P < 0.05), whereas no significant relationship was observed between GU and BF (r = 0.352, P = NS). Therefore, skeletal muscle FFAU, but not GU, appears to be associated with BF during low-intensity exercise. The present results also indicate considerable regional differences in substrate use within working QF muscle. As such, an important methodological outcome from these results is that one sample from a specific part of the QF muscle does not represent the response in the entire QF muscle group.

Physical fitness and anthropometrics in Finnish soldiers during their early career: prospective changes during a 3-year follow-up.

INTRODUCTION: Physical fitness is a fundamental capability required of military personnel, but studies focusing on longitudinal changes in physical fitness and anthropometrics in soldiers are lacking. The aim was to evaluate physical fitness and anthropometrics in soldiers during their early career. METHODS: A 3-year prospective study included 180 male soldiers (baseline age 26±2 years) with measures of a 12 min running test, standing long jump, sit-up and push-up tests, and body mass, height and waist circumference (WC). Baseline data were stratified into tertiles, and the changes within each tertile were analysed using dependent t-tests and analysis of variance. RESULTS: 12 min running test distance decreased on average by 2% (-54 m), sit-up performance 3% (-1.5 repetitions (reps)/min), push-up performance 4% (-1.9 reps/min) and standing long jump performance 1% (-2.1 cm) over the 3-year period (p<0.05). Both aerobic and muscular fitness decreased consistently among the highest baseline tertile (12 min running test: -70 m, sit-ups: -3.2 reps/min, push-ups: -7.5 reps/min, standing long jump: -5.5 cm; p<0.001), whereas both aerobic and muscular fitness levels were maintained and push-up performance was improved (p<0.05) in the lowest baseline tertiles. Body mass increased on average by 4% (+3.4 kg) and WC by 4% (+3.9 cm) (p<0.001), and these increases were observed for all baseline tertiles (p<0.05). CONCLUSIONS: Small decrements in physical fitness and anthropometrics exist during the early career of soldiers. The changes in physical fitness differed according to baseline fitness levels. The results indicate that support for exercise training may be needed even in a soldier's early career.

Changes in physical performance, body composition and physical training during military operations: systematic review and meta-analysis.

Systematic review and meta-analysis applying PRISMA guidelines with a PICOS format was constructed to provide an overview of changes in physical performance, body composition and physical training in soldiers during prolonged (≥ 3 months) military operations. Twenty-four studies out of the screened 4431 records filled the inclusion criteria. A small decrease in endurance performance was the most consistent finding (Hedge's g [g] - 0.21, 95% CI - 0.01 to - 0.41) while small overall increases in maximal strength of the lower (g 0.33, 95% CI 0.16-0.50) and upper body (g 0.33, 95% CI 0.19-0.46) were observed. In addition, small increases in strength endurance (push-up, g 0.34, 95% CI 0.15-0.52; sit-up g 0.26, 95% CI 0.07-0.44) were observed. The overall changes in body composition were trivial. Heterogeneity in the outcome variables varied mainly between low to moderate. Large inter-individual variations were observed in physical training volume, including decrements especially in endurance training frequency and volume. A reduction in total training load was often associated with negative changes in body composition and physical performance according to the principle of training specificity. Individuals with higher initial fitness level were more susceptible to decrements in their physical performance during operation.

Both poor cardiorespiratory and weak muscle fitness are related to a high concentration of oxidized low-density lipoprotein lipids.

Good physical fitness is associated with favorable serum lipids. Oxidized low-density lipoprotein (ox-LDL) could be even more atherogenic than serum lipids. We studied the association of ox-LDL and serum lipids with physical fitness. Healthy young (mean age 25 years) men (n=846) underwent maximal oxygen uptake (VO(2max)) and muscle fitness index (MFI) tests and completed a leisure-time physical activity (LTPA) questionnaire. Age (ANCOVA1), age+waist circumference+systolic blood pressure+fasting blood glucose+smoking (ANCOVA3) were used as covariates. The groups with the lowest VO(2max), MFI and LTPA had 23%, 16% and 8% higher concentrations of ox-LDL than the groups with the highest VO(2max) (P<0.0001), MFI (P=0.022) and LTPA (P=0.039) groups, respectively. Subjects with poor fitness (low VO(2max) or low MFI) or low LTPA had elevated levels of ox-LDL/high-density lipoprotein (HDL)-cholesterol, total cholesterol, LDL-cholesterol, triglycerides and a low level of HDL-cholesterol (ANCOVA1, in all, P<0.05). Furthermore, low VO(2max) is associated with a high level of ox-LDL/HDL-cholesterol and triglycerides, and with a low level of HDL-cholesterol (ANCOVA3, in all, P<0.05). Also, subjects with low LTPA had a high ratio of ox-LDL/HDL-cholesterol (ANCOVA1, P=0.001). In conclusion, both poor fitness (both low VO(2max) and low MFI) and low LTPA are associated with a higher concentration of ox-LDL lipids and serum lipids, which may indicate a higher risk for atherosclerosis.

Changes in physical fitness and anthropometrics differ between female and male recruits during the Finnish military service.

INTRODUCTION: Military training programmes are often similar for male and female recruits despite sex differences in physical performance that may influence training adaptations during military service. The present study aimed to compare changes in physical fitness and anthropometrics between Finnish female and male recruits during military service. METHODS: A total of 234 690 male and 3549 female recruits participated in fitness tests at the beginning and end of military service between 2005 and 2015. Anthropometric measurements were body mass, height, body mass index (BMI) and waist circumference (WC). Fitness tests consisted 12 min running, standing long jump, and sit-ups and push-ups. RESULTS: No changes were observed in anthropometrics, while both sexes improved most of the fitness test results. After adjustment for service time, branch, age, initial fitness test results, BMI and WC, improvement in running test performance was 158 m (95% CI 142 to 173, p≤0.001) greater in male than female recruits. Similarly, improvements were larger in male recruits for push-ups (5 reps/min, 95% CI 5 to 6, p≤0.001), sit-ups (2 reps/min, 95% CI 2 to 3, p≤0.001) and standing long jump (12 cm, 95% CI 11 to 13, p≤0.001) when compared with women. CONCLUSIONS: The study revealed sex differences in adaptations to the standardised military training. Both male and female recruits improved their physical fitness, but smaller gains were observed in women using the same training programme. The mechanisms explaining sex differences in adaptations to military training, and whether tailored training programmes are needed specifically for female recruits to reduce sex differences during military service, warrants further studies.

Aerobic fitness predicted by demographics, anthropometrics, health behaviour, physical activity and muscle fitness in male and female recruits entering military service.

INTRODUCTION: The physical and mental training load can be high during military service. Therefore, tailored preconditioning programmes based on assessment of physical fitness could increase readiness for military service, especially among those ones with lower baseline fitness level. The purpose of present study was to investigate how self-assessed health behaviour, physical activity and muscle fitness can predict physical fitness in young male and female military cohorts. METHODS: Demographics, health behaviour and daily physical activity preceding military service were surveyed by a questionnaire. Thereafter, physical fitness was assessed during the military service by the tests of 12 min running, 1 min push-ups and sit-ups. Explosive power of the lower extremities was studied by maximal standing long jump. Measurements of body anthropometry consisted of body mass, height, and waist circumference. RESULTS: The two strongest individual predictors of objectively measured running distance in 12 min were self-reported physical activity and physical readiness in both men and women. Self-reported physical activity, readiness for military service, sitting time, education, smoking and body anthropometrics together explained 52% of the variance in the 12 min running test result (R2=0.52, mean absolute percentage error (MAPE) 8.8%, mean absolute error (MAE) 207 m) in men, while for women the predictive values were weaker. Addition of muscle fitness results to the adjusted regression model further improved the model, which explained 59% of the variance in the 12 min running tests result of male conscripts (R2=0.59, MAPE 7.8%, MAE 181 m). CONCLUSION: In the present study, self-reported physical activity, muscle fitness, physical readiness for military service, sitting time, education, smoking and body anthropometrics predicted inadequately the measured endurance capacity among recruits. The present questionnaire-based variables do not accurately predict physical fitness of recruits and thus, they are not either suitable for practical use for preconditioning programmes or preselection before entering the military service.

Aerobic fitness, energy balance, and body mass index are associated with training load assessed by activity energy expenditure.

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.

Effects of 10 weeks of military training on neuromuscular function in non-overreached and overreached conscripts.

The purpose of the study was to examine how military training influences neuromuscular function in non-overreached and overreached conscripts. A total of 24 male conscripts participated in the study (8 weeks basic training + 2 weeks specialized training). All measurements were conducted during weeks 1, 5, 8 and 10. After the training period, non-overreached (NOR, n = 16) and overreached (OR, n = 8) groups were compared. Isometric maximal forces (bench press, elbow flexion and knee extension), single twitch (plantar flexors), H-reflex, M-wave (Hmax/Mmax) and V-wave (V/Mmax) (soleus) were measured. In knee extension, force production increased in NOR by 22.5 ±â€¯20.5% (p < 0.01) between weeks 1 and 8, which was not observed in OR (-1.1 ±â€¯18.2%, p > 0.05). In OR, plantarflexion twitch contraction time increased between weeks 5 and 10 by 82.2 ±â€¯34.4% (p < 0.01), which was not observed in NOR. No changes were observed in the H-reflex and V-wave responses in either of the groups. In conclusion, short term overreaching can also reduce the performance of the neuromuscular system, however, it seems to be more muscle than neural based. To avoid overreaching, more individualized periodization should be used during basic training. To enhance neuromuscular performance, maximal and explosive strength training should also be added into the basic training program.

Active recovery shows favorable IGF-I and IGF binding protein responses following heavy resistance exercise compared to passive recovery.

IGF-I and IGFBPs have important physiological modulatory effects and this study sought to examine the influence of active vs. passive recovery following a heavy resistance exercise on IGF-I and IGF binding protein (IGFBP) recovery responses. It was hypothesized that increased IGF-I and decreased inhibitory IGFBPs during active recovery may be reflective of cascades promoting physiological recovery. 18 untrained men ((AR n = 7, PR n = 11), age: 26 ±â€¯4 years, height: 174 ±â€¯8 cm, body mass: 75 ±â€¯13 kg) performed either a protocol-specific 10 × 10 × 30% 1RM active (AR) or passive recovery (PR) session following a heavy resistance exercise session performed on a leg press device (10 × 10 1RM). Maximal isometric force production (MVC) and IGF- and IGFBPs were measured pre, post, 1-hr post, and next morning. A significantly greater relative response in IGF-I was observed in AR than in PR at post recovery and next morning (p < .01 and statistical trend, respectively) while absolute concentrations of IGFBP-1 at next morning were significantly higher in PR than AR (p < .05), and relative IGFBP-1 response from control to next morning in PR was significantly greater than in AR (p < .001). IGFBP-1 may be inhibitory to IGF-I biological action, thus the lower concentration of IGFBP-1 after AR may be considered favorable in terms of recovery due to its positive relationship with glucose metabolism and maintaining metabolic homeostasis. These results suggest that some of the benefits of an active recovery bout may be mediated by favorable IGF-I system responses (increased IGF-I and decreased IGFBP-1) in the hormonal milieu that may assist facilitating the cascade of physiological recovery processes following acute heavy resistance loading exercise.

Molecular adaptations of voltage-gated sodium ion channel related proteins after fatiguing stretch-shortening cycle exercise.

Dystrophin associated protein alpha-syntrophin is known to interact with voltage-gated sodium ion channel (NaCh). Dystrophin is known to be sensitive to eccentric muscle actions. For this reason, the function of the NaChs might also be affected. Molecular adaptations of dystrophin, alpha-syntrophin and NaChs were investigated after fatiguing stretch-shortening cycle (SSC) exercise, which consisted of unilateral jumps on a sledge apparatus. Muscle biopsies were taken from the vastus lateralis muscle of eight healthy subjects immediately after (IA) and 2 days after (2D) the exercise to analyze mRNA levels and immunohistochemical staining patterns. SSC exercise resulted in decreased isometric maximal voluntary contraction (IA: -31+/-9%, 2D: -14+/-16%) and a delayed increase of plasma creatine kinase activity (2D: +178+/-211%). Despite muscle soreness (P<0.001), no morphological damage was observed and no changes were found in the mRNA concentrations. However, the relative changes of the mRNA concentrations of alpha-syntrophin and NaChs were highly correlated (r=0.93, P<0.001) 2D after SSC exercise. This consistent pattern of mRNA regulation may imply a functional relationship between these two proteins. In addition, the current experiment emphasises high inter-individual variation in molecular responses to heavy exercise.

Mineral mass, size, and estimated mechanical strength of triple jumpers' lower limb.

This study was designed to examine the anticipated strong influence of extreme impact loading on the mineral mass, size, and gross structural properties of triple jumpers' lower limb bones. We compared the bone data obtained with peripheral quantitative computed tomography (pQCT) and dual-energy X-ray absorptiometry (DXA) from 8 Finnish triple jumpers with corresponding data from gender-, age-, height-, and weight-matched nonathletic peers. The volumetric (trabecular) density was significantly higher in the jumpers than in controls (from an average 18% difference at the distal tibia to a 41% difference at the proximal tibia), whereas the cortical density did not differ between groups. The DXA-derived areal bone mineral density of the femoral neck and lumbar spine was 31% higher in the jumpers than in controls, compared with a 16% difference between groups at the less-loaded distal radius. The lower limb bones were comparable in size between groups except at the distal femur where a significant 4%-6% difference was observed in favor of the triple jumpers. Mean tibial cortical wall thickness and area were substantially greater in the triple jumpers; the mean group difference ranged from about 20% at the shaft sites, to over 50% at the distal tibia. Given the apparently stronger cortices in the triple jumpers, the section moduli (bone strength index) of their femoral necks and tibiae were 19%-31% higher compared with the control group. Our findings indicate the ability of extreme impact loading to considerably improve bone's mechanical competence. Adaptation to loading seems to occur in a site-specific fashion by gross geometric changes, structural or architectural changes, or by their combination. The loading effect was best seen as enlarged bone cortices, probably after the trabecular density had reached its ceiling.

Altered reflex sensitivity after repeated and prolonged passive muscle stretching.

Experiments were carried out to test the effect of prolonged and repeated passive stretching (RPS) of the triceps surae muscle on reflex sensitivity. The results demonstrated a clear deterioration of muscle function immediately after RPS. Maximal voluntary contraction, average electromyographic activity of the gastrocnemius and soleus muscles, and zero crossing rate of the soleus muscle (recorded from 50% maximal voluntary contraction) decreased on average by 23.2, 19.9, 16.5, and 12.2%, respectively. These changes were associated with a clear immediate reduction in the reflex sensitivity; stretch reflex peak-to-peak amplitude decreased by 84. 8%, and the ratio of the electrically induced maximal Hoffmann reflex to the maximal mass compound action potential decreased by 43. 8%. Interestingly, a significant (P < 0.01) reduction in the stretch-resisting force of the measured muscles was observed. Serum creatine kinase activity stayed unaltered. This study presents evidence that the mechanism that decreases the sensitivity of short-latency reflexes can be activated because of RPS. The origin of this system seems to be a reduction in the activity of the large-diameter afferents, resulting from the reduced sensitivity of the muscle spindles to repeated stretch.

Reduced reflex sensitivity persists several days after long-lasting stretch-shortening cycle exercise.

The mechanisms related to the acute and delayed secondary impairment of the stretch reflex function were investigated after long-lasting stretch-shortening cycle exercise. The results demonstrated a clear deterioration in muscle function immediately after fatigue, which was accompanied by a clear reduction in active and passive reflex sensitivity. For active and passive stretch reflexes, this reduction was biphasic (P < 0.05 to P < 0.001). However, for the ratio of the electrically induced maximal Hoffmann reflex to the maximal mass compound action potential, only one significant reduction was seen immediately after fatigue (71.2%, P < 0.01). A similar significant (P < 0.01) decrease in the stretch-resisting force of the muscle was also detected. Clear increases were found in the indirect markers of muscle damage (serum creatine kinese activity and skeletal troponin I), which could imply the occurrence of ultrastructural muscle damage. It is suggested that the acute reduction in reflex sensitivity is of reflex origin and due to two active mechanisms, disfacilitation and presynaptic inhibition. However, the delayed second decline in the sensitivity of some reflex parameters may be attributable to the secondary injury, because of some inflammatory response to the muscle damage. This might emphasize the role of presynaptic inhibition via group III and IV muscle afferents.