Changes in haemoglobin and ferritin levels during basic combat training: relevance for attrition and injury frequency.

INTRODUCTION: The primary aim of the present study was to assess interindividual and intraindividual variations in haemoglobin and ferritin concentrations in Swedish recruits over 5 months of basic combat training (BCT). The secondary aim was to find predictors for missing training (a precursor for attrition) and overuse injuries during BCT. METHODS: In a cohort design, a total of 58 female and 104 male recruits provided complete data. We assessed the ferritin concentrations and haemoglobin concentrations at baseline and after 5 months of BCT and physical work capacity at baseline. RESULTS: During BCT, haemoglobin concentrations increased significantly in both females and males. Ferritin concentrations decreased significantly in both sexes and the prevalence of iron deficiency (ID) (ie, ferritin levels <30 µg/L) increased significantly in females. The physical work capacity at baseline was related to the risk of missing training in fully adjusted models. In gender-adjusted analyses, baseline ferritin was related to the risk of overuse injury, but neither baseline nor change in iron status was related to injuries or risk of missing training when controlling for confounders. Body mass increased significantly in both genders, but we found no correlation between individual change in body mass and change in haemoglobin or ferritin nor was change in body mass related to the risk of overuse injury or missing training. CONCLUSION: In the present study, the prevalence of ID increased over the course of 5 months, while haemoglobin concentrations increased. As baseline physical work capacity was related to missing training, there are reasons to support preparatory physical training before BCT. These findings may inform future preventive interventions aimed at preventing detrimental effects of ID.

Fundament for a methodological standard to process hip accelerometer data to a measure of physical activity intensity in middle-aged individuals.

BACKGROUND: There is a lack of a methodological standard to process accelerometer data to measures of physical activity, which impairs data quality and comparability. This study investigated the effect of different combinations of settings of multiple processing components, on the measure of physical activity and the association with measures of cardiometabolic health in an unselected population of middle-aged individuals. METHODS: Free-living hip accelerometer data, aerobic fitness, body mass index, HDL:total cholesterol ratio, blood glucose, and systolic blood pressure were achieved from 4391 participants 50-64 years old included in The Swedish CArdioPulmonary bioImage Study (SCAPIS) baseline measurement (cross-sectional). Lab data were also included for calibration of accelerometers to provide comparable measure of physical activity intensity and time spent in different intensity categories, as well as to enhance understanding. The accelerometer data processing components were hardware recalibration, frequency filtering, number of accelerometer axes, epoch length, wear time criterium, time composition (min/24 h vs. % of wear time). Partial least regression and ordinary least regression were used for the association analyses. RESULTS: The setting of frequency filter had the strongest effect on the physical activity intensity measure and time distribution in different intensity categories followed by epoch length and number of accelerometer axes. Wear time criterium and recalibration of accelerometer data were less important. The setting of frequency filter and epoch length also showed consistent important effect on the associations with the different measures of cardiometabolic health, while the effect of recalibration, number of accelerometer axes, wear time criterium and expression of time composition was less consistent and less important. There was a large range in explained variance of the measures of cardiometabolic health depending on the combination of processing settings, for example, 12.1%-20.8% for aerobic fitness and 5.8%-14.0% for body mass index. CONCLUSIONS: There was a large variation in the physical activity intensity measure and the association with different measures of cardiometabolic health depending on the combination of settings of accelerometer data processing components. The results provide a fundament for a standard to process hip accelerometer data to assess the physical activity in middle-aged populations.

Acute effects of physical activity patterns on plasma cortisol and brain-derived neurotrophic factor in relation to corticospinal excitability.

Brain-derived neurotrophic factor (BDNF) and cortisol are both capable of modulating synaptic plasticity, but it is unknown how physical activity-induced changes in their plasma levels relate to corticospinal plasticity in humans. Sixteen inactive middle-aged men and women participated in three separate interventions consisting of 3 h prolonged sitting (SIT); 3 h sitting interrupted every 30 min with frequent short physical activity breaks (FPA); and 2.5 h prolonged sitting followed by 25 min of moderate intensity exercise (EXE). These 3 h sessions were each followed by a 30 min period of paired associative stimulation over the primary motor cortex (PAS). Blood samples were taken and corticospinal excitability measured at baseline, pre PAS, 5 min and 30 min post PAS. Here we report levels of plasma BDNF and cortisol over three activity conditions and relate these levels to previously published changes in corticospinal excitability of a non-activated thumb muscle. There was no interaction between time and condition in BDNF, but cortisol levels were significantly higher after EXE compared to after SIT and FPA. Higher cortisol levels at pre PAS predicted larger increases in corticospinal excitability from baseline to all subsequent time points in the FPA condition only, while levels of BDNF at pre PAS did not predict such changes in any of the conditions. Neither BDNF nor cortisol modified changes from pre PAS to the subsequent time points, suggesting that the increased corticospinal excitability was not mediated though an augmented effect of the PAS protocol. The relationship between cortisol and plasticity has been suggested to be inverted U-shaped. This is possibly why the moderately high levels of cortisol seen in the FPA condition were positively associated with changes AURC, while the higher cortisol levels seen after EXE were not. A better understanding of the mechanisms for how feasible physical activity breaks affect neuroplasticity can inform the theoretical framework for how work environments and schedules should be designed.

The effect of breaking up prolonged sitting on paired associative stimulation-induced plasticity.

Paired associative stimulation (PAS) can induce plasticity in the motor cortex, as measured by changes in corticospinal excitability (CSE). This effect is attenuated in older and less active individuals. Although a single bout of exercise enhances PAS-induced plasticity in young, physically inactive adults, it is not yet known if physical activity interventions affect PAS-induced neuroplasticity in middle-aged inactive individuals. Sixteen inactive middle-aged office workers participated in a randomized cross-over design investigating how CSE and short-interval intracortical inhibition (SICI) were affected by PAS preceded by 3 h of sitting (SIT), 3 h of sitting interrupted every 30 min by 3 min of frequent short bouts of physical activity (FPA) and 2.5 h of sitting followed by 25 min of moderate-intensity exercise (EXE). Transcranial magnetic stimulation was applied over the primary motor cortex (M1) of the dominant abductor pollicis brevis to induce recruitment curves before and 5 min and 30 min post-PAS. Linear mixed models were used to compare changes in CSE using time and condition as fixed effects and subjects as random effects. There was a main effect of time on CSE and planned within-condition comparisons showed that CSE was significantly increased from baseline to 5 min and 30 min post-PAS, in the FPA condition, with no significant changes in the SIT or EXE conditions. SICI decreased from baseline to 5 min post-PAS, but this was not related to changes in CSE. Our findings suggest that in middle-aged inactive adults, FPAs may promote corticospinal neuroplasticity. Possible mechanisms are discussed.

Association of perceived physical health and physical fitness in two Swedish national samples from 1990 and 2015.

Perceived health and physical fitness have been shown to correlate, and low levels of either variable increase the risk for future illness and mortality. However, risk factors and their interrelationship may vary between societies and over time. In this study, the associations of physical fitness and perceived health were therefore assessed in two Swedish national samples 25 years apart. Perceived physical health, dichotomized as "good" or "bad," maximal oxygen uptake (VO2 max), counter movement jump (CMJ), balance (one-legged 60 second stance), and self-reported demographics and lifestyle were recorded in two cross-sectional samples (sample size, number of eligible participants) of Swedish adults, aged 20-65 years, in 1990-1991 (2203, 1365), and 2013-2015 (3357, 422). The odds for good perceived physical health increased by 5% per mL·kg-1 ·min-1 of VO2 max, 3% per cm CMJ height, and decreased by 4% per 1 time of overbalancing, in both samples. Mutually adjusted regression models showed that perceived physical health was best predicted by VO2 max and chronic illness in 1990 and by age, BMI, and educational level in 2015. CONCLUSION: Perceived physical health was related to physical fitness in two samples of Swedish adults from 1990 and 2015. However, multivariate and mutually adjusted models indicate that the most important covariates of perceived physical health may have changed from VO2 max and chronic illness in 1990, to age, BMI, and educational level in 2015.

Fitness and abdominal obesity are independently associated with cardiovascular risk.

OBJECTIVES: To examine the relationship between cardiovascular fitness (VO(2)max) and abdominal obesity (waist circumference) and individual cardiovascular disease (CVD) risk factors, as well as a clustered risk factor profile, and to study the impact of gender, age and smoking on these relationships. DESIGN: Cross-sectional. SETTING: Astrand Laboratory of Work Physiology, Swedish School of Sport and Health Sciences, Stockholm, Sweden. SUBJECTS: Men (n = 781) and women (n = 890) from two random population-based samples of Swedish women and men aged 20 to 65 years. MAIN OUTCOMES: Odds ratios. RESULTS: Each unit of higher fitness was associated with a decrease in all individual risk factors ranging from 2% to 4% independent of waist circumference, each unit of higher waist circumference was associated with an increased risk ranging from 2% to 5% independent of fitness. For clustering of three or more of the risk factors, each unit of fitness was associated with a 5% decrease in risk and each unit of waist circumference with a 5% increase in risk. The clustered risk was higher in unfit participants who were older or smoked daily, regardless of waist circumference. Obese participants were at higher risk if they were men or older, regardless of fitness level. However, neither a higher fitness level nor lean status reduced the risk associated with smoking. CONCLUSIONS: Higher fitness and lower waist circumference are each independently associated to a similar extent with a lower CVD risk. Simultaneous evaluation of both fitness and abdominal obesity status in clinical practice is important.

Secular trends of physical fitness in Swedish adults.

The aim of the present study was to study differences in fitness (maximal aerobic power (VO(2max)), balance control, abdominal strength and endurance) and anthropometric data in Swedish women and men (20-65 years of age) between two national cross-sectional samples, studied in 1990/1991 and 2000/2001, respectively. The absolute and relative VO(2max) (aerobic fitness), estimated from a submaximal test, declined with increasing age in both genders. The submaximal test was validated against running VO(2max). Furthermore, the relative aerobic fitness (mL/min/kg) was lower in the 2000/2001 sample in men but not in women. Overall physical activity level was unchanged in both genders. An unexpected finding was that in both samples there were no major differences in relative VO(2max) between men and women of the same age. Combined overweight and obesity (body mass index> or =25) is becoming more prevalent in men, but not in women with prevalence in 2000/2001 of 61% and 38% for men and women, respectively. Balance control and abdominal strength and endurance decrease with increasing age with no differences between the two samples. Thus, the near future health situation for men may be worse, while for women it may be less or no differences compared with today.

Infectious episodes before and after a marathon race.

The aim of this study was to investigate the incidence of self-reported infectious episodes (IE) during 3 weeks before (pre-IE) and 3 weeks after (post-IE) a marathon race and relate these figures to training status, running time, socioeconomic and demographic factors. Two questionnaires, including questions about important factors for IE incidence, were given to a representative cohort of 1694 runners (17% of all finishers) in the Stockholm Marathon 2000. Pre-IE incidence in the cohort was 17% with no difference between women and men. Post-IE incidence in the whole cohort was 19% with no significant (P>0.05) difference between women and men. The post-IE incidence in runners without a pre-IE was 16% (P>0.05 to pre-IE incidence). In the group of runners with pre-IE, 33% experienced an IE after the race also (P<0.05 to Pre-IE incidence). A logistic regression analysis showed that younger age and pre race health status and, for men only, experienced nausea during and after the race were depended factors explaining post-IE incidence. Younger runners were more prone to experience IE both before and after the race. There was no relation between training volume 6 months before the race, finishing time and socioeconomic and demographic factors and pre-IE or post-IE. This study does not support the theory of increased infection rate after exhaustive long-distance running ("The Open Window Theory") in recreational runners, but suggests that the sometimes experienced increased rate of infections among athletes can be caused by strenuous exercise too soon after an infection.

Immune system alteration in response to increased physical training during a five day soccer training camp.

Leukocyte and monocyte subpopulations were investigated in ten elite male soccer players before and after a 5-day training camp. It was hypothesized that with increased training intensity and duration, the immune system would show signs of depression. Blood samples were taken at rest before and after the training camp and cell surface antigens were investigated by four-colour flow cytometry. After five days of intensified training, there was a significant decrease in the number of T helper, T cytotoxic and B cells, the expression of CD11 b on leukocytes increased and the NK cell population did not change significantly. It is concluded that after a period of intensified training, soccer players may experience decreased T and B cell numbers in circulation, possibly affecting their capability to activate the immune system and resist infections. However, in contrast to the acute decrease in the number of circulating NK cells commonly observed after physical exercise, no change in this cell population was observed at rest after a period of intensified physical training. Exercise-induced immunological changes were highly differentiated between different leukocyte subpopulations.

Health-related fitness in Swedish adolescents between 1987 and 2001.

AIM: To assess trends in neuro-muscular and cardio-respiratory fitness and morphological fitness in Swedish adolescents between 1987 and 2001. METHODS: Comparison of data from two samples, one from 1987 (n = 479) and one from 2001 (n = 1470). Subjects underwent functional tests of muscular strength in the lower limbs, trunk and upper body, sub-maximal ergometrics, and measurement of body mass and height. RESULTS: Cardio-respiratory fitness showed only small changes between 1987 and 2001 among boys, with no changes in girls. Neuro-muscular fitness, as measured by three functional tests, was lower in 2001 compared to 1987. The most pronounced changes in these functional tests were found in the arm-hang test, while changes in lower body and trunk strength tests were less. Our results indicate that the difference in the prevalence of overweight in adolescents between 1987 and 2001 is mainly due to a large change in the most unfit group. The fittest group showed only marginal changes. CONCLUSION: We suggest that the differences in neuro-muscular fitness are at least partly due to differences in the amount and nature of physical activity, and that this might lead to consequences for health later in life.

Immune system alteration in response to two consecutive soccer games.

AIM: Changes in leucocyte and monocyte subpopulations were investigated in 10 elite male soccer players aged 16-19 years. The purpose was to perform a descriptive study of immunological alterations in elite soccer players in response to two consecutive games separated by 20 h. It was hypothesized that in response to two games the players would show signs of short-term immunosuppression. METHODS: Blood samples were taken before the first soccer game, immediately after the second game and after 6, 24, 48 and 72 h. Cell surface antigens, testosterone and cortisol were investigated. RESULTS: During the first 6 h after the second game there was a significant increase in number of circulating neutrophils, mature (CD20+ CD5+) B cells and CD4/CD8 ratio. A significant decrease was observed in the number of natural killer (NK) cells, monocytes and adhesion on lymphocytes and monocytes. In a delayed phase, 48 h after the second game the expression of both adhesion and signalling molecules increased on lymphocytes and monocytes. Changes in adhesion and signalling molecules at 48 h correlated negatively to the subjects VO2max, suggesting larger immunological response to similar exercise in subjects with lower aerobic exercise capacity. CONCLUSION: In response to competitive soccer exercise some immunological variables are enhanced while others are depressed. Observed changes may serve a purpose in adaptation to exercise by signalling via adhesion.

Mortality amongst participants in Vasaloppet: a classical long-distance ski race in Sweden.

OBJECTIVE: The aim of this study was to assess mortality amongst participants in long-distance ski races during the Vasaloppet week. We considered the 90 km races for men and 90 or 30 km for women. The vast majority of the participants in these races are not competing on the elite level. It is assumed, however, that they have to undergo regular physical training during a long period of time in order to successfully finish the race. DESIGN: The cohort study consisted of 49 219 men and 24 403 women, who participated in any of the races during 1989-1998. All subjects were followed up in the National-Cause-of-Death-Register until 31 December 1999. We computed the standardized mortality ratios (SMRs) adjusting for age and calendar year. RESULTS: Overall, 410 deaths occurred, compared with 850.6 expected, yielding an SMR of 0.48 [95% confidence interval (CI) 0.44-0.53]. Low SMRs were found in all age groups in both men and women and in all groups after categorization by finishing time and number of races. The lowest SMRs were found amongst older participants and in those who participated in several races. A decreased mortality was observed in all major diagnostic groups, namely cancers (SMR = 0.61; 95% CI 0.52-0.71), diseases of the circulatory system (SMR = 0.43; 95% CI 0.35-0.51), and injuries and poisoning (SMR = 0.73; 95% CI 0.60-0.89). For lung cancer the SMR was 0.22, but even after exclusion of lung cancer the all-cancer mortality was low (SMR = 0.72; 95% CI 0.59-0.86). CONCLUSIONS: We conclude that participants in long-distance skiing races, which demand prolonged regular physical training, have low mortality. The extent to which this is due to physical activity, related lifestyle factors, genetics or selection bias is yet to be assessed.

Adaptive stress response of glutathione and uric acid metabolism in man following controlled exercise and diet.

Ergometer cycling performance as well as acute exercise-induced changes in the metabolism of energy-intermediates and glutathione (GSH) were investigated in skeletal muscle (SM) of 15 healthy young male subjects (VO(2max) approximately 54.7 mL kg(-1) min(-1), age approximately 25 years), before and after 3 days of controlled 'ìoverload-training' in combination with either high (62% of energy intake) or low (26% of energy intake) dietary intake of carbohydrates. The intake of a carbohydrate-rich diet clearly reduced the depletion of SM glycogen following the short-term training period, paralleled with a positive effect on the endurance performance, but not on high-intensity work-performance. An 'delayed over-reaching effect', defined as impaired work-performance, was observed after 2.5 days of recovery from the short-term training period, irrespective of the carbohydrate content of the diet and basal glycogen level in SM. Taken together, the main and novel findings of present investigation are: (1) an acute decrease of reduced GSH content and altered thiol-redox homeostasis in SM induced by strenuous high-intensity exercise; (2) an adaptive elevation of basal GSH level following the short-term training period; (3) an adaptive decrease of basal GSH level following 2.5 days recovery from training; (4) evidence of a relationship between the SM fibre type, physical performance capacity and GSH turnover during acute bouts of exercise; and (5) no evident effect of the level of carbohydrate intake on metabolism of GSH or energy intermediates. Furthermore, the induction of acute oxidative stress in exercising human SM and the adaptive responses to training are suggested to provide a protective antioxidant phenotype to the exercising SM during periods with repeated intense intermittent training.