Background Maintenance of lean muscle mass and related strength is associated with lower risk for numerous chronic diseases of aging in women. Objective Our aim was to evaluate whether the association between dietary protein and lean mass differs by physical activity level, amino acid composition, and body mass index categories. Design We performed a cross-sectional analysis of a prospective cohort. Participants/setting Participants were postmenopausal women from the Womens Health Initiative with body composition measurements by dual-energy x-ray absorptiometry (n=8,298). Main outcome measures Our study measured percent lean mass, percent fat mass, and lean body mass index. Statistical analyses performed Linear regression models adjusted for scanner serial number, age, calibrated energy intake, race/ethnicity, neighborhood socioeconomic status, and recreational physical activity were used to determine the relationship between protein intake and body composition measures. Likelihood ratio tests and stratified analysis were used to investigate physical activity and body mass index as potential effect modifiers. Results Biomarker-calibrated protein intake was positively associated with percent lean mass; women in the highest protein quintile had 6.3 percentage points higher lean mass than the lowest quintile (P<0.001). This difference rose to 8.5 percentage points for physically active women in the highest protein quintile (P-interaction=0.023). Percent fat mass and lean body mass index were both inversely related to protein intake (both P<0.001). Physical activity further reduced percent fat mass (P-interaction=0.022) and lean body mass index (P-interaction=0.011). Leucine intake was associated with lean mass, as were branched chain amino acids combined (both P<0.001), but not independent of total protein. All associations were observed for normal-weight, overweight, and obese women. Conclusions Protein consumption up to 2.02 g/kg body weight daily is positively associated with lean mass in postmenopausal women. Importantly, those that also engage in physical activity have the highest lean mass across body mass index categories.

Due to the widespread use of the endocrine disruptors Bisphenol-A (BPA) and phthalates in many plastic consumer goods, medical equipment, and personal care products, more than 95% of the US population show detectable levels of urinary BPA and phthalate metabolites. Both have been linked to increased body mass index (BMI in kg/m2), an inexpensive diagnostic tool for obesity, which may however not reflect body fatness. Since excess body fat is associated with cardiovascular diseases, cancer and type II diabetes, it is important to understand the relationship between body fat composition and exposure to BPA and phthalates, a relationship that is still unknown. Using NHANES 1999-2006 data on adults aged >20 years, we investigated the relationship between urinary BPA (N=2,534), monoethyl-phthalate (mEP, N=5,431), monobutyl-phthalate (mBP), monoethylhexyl-phthalate (mEHP) and monobenzyl-phthalate (mBzP, each N=5,436) measured by high-performance liquid chromatography tandem mass spectrometry, and body fat composition measured as lean mass (LM, grams), fat mass (FM, grams) and percent body fat (%BF) using Dual Energy X-ray Absorptiometry. A multivariable linear regression analysis yielded that independently of BMI, BPA, mBP, and mBzP were inversely associated with LM (quartile 4 b=-862.16 (354.65), -731.76 (248.89), -909.13 (252.32), respectively; all p<0.02, p-trend<0.02); mEHP and FM were inversely associated (quartile 4 b=-297.98 (144.87), p=0.04, p-trend<0.02); BPA, mBP, and mBzP were positively associated with %BF but not clinically significant. These results provide novel insights in the relationship between urinary BPA, phthalates and LM independent of BMI, and it highlights the need for prospective studies establishing temporality of this relationship.

Background In South Africa, as in many other developing countries, obesity has become a major health problem causing an increase in the incidence and prevalence of various non-communicable diseases. Research has shown that excess adiposity is associated with low vitamin D status and detrimental to bone health. Low vitamin D status has been linked to various non-communicable diseases which includes osteoporosis, and also the metabolic syndrome. Information is scarce on the role of lean mass and fat mass on bone health in the black South African population. There is also a shortage of data on the association between vitamin D status and the metabolic syndrome in the South African population. Aim The main aim of this study was to examine factors (vitamin D status, socio-economic status [SES] and lifestyle risk factors) associated with body composition, including bone health, as well as predictors of change in body composition in African adults in the North West Province of South Africa. Methods The first study that forms part of this thesis was a longitudinal study aimed at examining the effects of urbanization, socio-economic status and lifestyle factors on changes in body composition over 5 years in rural and urban black South African adults. A total of 1058 men and women above age 30 years from the Prospective Urban Rural Epidemiology study were included in this study. The second study to form part of this thesis aimed to examine the association between body composition and bone health in urban black South African women. Structured questionnaires were used to collect socio-demographic and lifestyle information including medication and tobacco use. This second study is cross-sectional in design and it included 189 postmenopausal women aged > 43 years old. Dual X-ray absorptiometry was used to assess bone mineral density, lean mass and fat mass, while structured and specific questionnaires were used to assess the habitual physical activity, food frequency and fracture risk. Habitual activity energy expenditure was also measured using an accelerometer with a combined heart rate monitor. The third study aimed to examine the association of serum 25 hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) concentration, respectively, with the metabolic syndrome while controlling for adiposity in black women in the North West Province, South Africa. This third study is also cross-sectional in design and it included 209 HIV-negative urban women. Dual X-ray absorptiometry was used to assess adiposity, while habitual physical activity was accessed with questionnaire and habitual activity energy expenditure was also measured using an accelerometer with a combined heart rate monitor. Results Study 1: Over a 5-year period, body mass index (BMI) and waist circumference increased in both genders, but the change was significant for BMI (P<0.01) and waist circumference (P<0.001) in women only, indicating an increase in adiposity over time. Urban residency positively predicted changes in waist circumference in men (p < 0.05) and women (p < 0.001) as well as change in triceps skinfold thickness of men (p < 0.05). Being married positively predicted changes in BMI (p < 0.001) and waist circumference (p < 0.001) in men, while age negatively predicted changes in triceps skinfold thickness in women (p < 0.001). Study 2: Fat mass and lean mass were significantly positively associated with bone mineral density (BMD) and fracture risk when adjusted for potential confounders. However, lean mass and not fat mass remained significantly associated with femoral neck BMD (β = 0.49, p <0.001), spine BMD (β = 0.48, p< 0.0001) and hip BMD (β = 0.59, p< 0.0001). Lean mass was also negatively associated with fracture risk (β = -0.19 p =0.04) when both lean and fat mass were in the same model. Study 3: After adjusting for age, body fat, habitual physical activity, tobacco use and season, neither 25(OH)D nor PTH concentrations showed significant associations with having the metabolic syndrome. However, when body fat was replaced with waist circumference there was a weak positive association between 25(OH)D concentration and the metabolic syndrome. No significant association was found between PTH:25(OH)D ratio and the metabolic syndrome. Conclusion This thesis has highlighted that the prevalence of obesity among black South Africans is high particularly among women and urbanization played a significant role in the increasing adiposity of black South Africans in the North West province. Lean mass had a stronger association with bone health in comparison to fat mass in urban black South African women. Low 25(OH)D concentration was not associated with the metabolic syndrome while there was no significant association between PTH and the metabolic syndrome in our black South African women. / PhD (Dietetics), North-West University, Potchefstroom Campus, 2015

Background In South Africa, as in many other developing countries, obesity has become a major health problem causing an increase in the incidence and prevalence of various non-communicable diseases. Research has shown that excess adiposity is associated with low vitamin D status and detrimental to bone health. Low vitamin D status has been linked to various non-communicable diseases which includes osteoporosis, and also the metabolic syndrome. Information is scarce on the role of lean mass and fat mass on bone health in the black South African population. There is also a shortage of data on the association between vitamin D status and the metabolic syndrome in the South African population. Aim The main aim of this study was to examine factors (vitamin D status, socio-economic status [SES] and lifestyle risk factors) associated with body composition, including bone health, as well as predictors of change in body composition in African adults in the North West Province of South Africa. Methods The first study that forms part of this thesis was a longitudinal study aimed at examining the effects of urbanization, socio-economic status and lifestyle factors on changes in body composition over 5 years in rural and urban black South African adults. A total of 1058 men and women above age 30 years from the Prospective Urban Rural Epidemiology study were included in this study. The second study to form part of this thesis aimed to examine the association between body composition and bone health in urban black South African women. Structured questionnaires were used to collect socio-demographic and lifestyle information including medication and tobacco use. This second study is cross-sectional in design and it included 189 postmenopausal women aged > 43 years old. Dual X-ray absorptiometry was used to assess bone mineral density, lean mass and fat mass, while structured and specific questionnaires were used to assess the habitual physical activity, food frequency and fracture risk. Habitual activity energy expenditure was also measured using an accelerometer with a combined heart rate monitor. The third study aimed to examine the association of serum 25 hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) concentration, respectively, with the metabolic syndrome while controlling for adiposity in black women in the North West Province, South Africa. This third study is also cross-sectional in design and it included 209 HIV-negative urban women. Dual X-ray absorptiometry was used to assess adiposity, while habitual physical activity was accessed with questionnaire and habitual activity energy expenditure was also measured using an accelerometer with a combined heart rate monitor. Results Study 1: Over a 5-year period, body mass index (BMI) and waist circumference increased in both genders, but the change was significant for BMI (P<0.01) and waist circumference (P<0.001) in women only, indicating an increase in adiposity over time. Urban residency positively predicted changes in waist circumference in men (p < 0.05) and women (p < 0.001) as well as change in triceps skinfold thickness of men (p < 0.05). Being married positively predicted changes in BMI (p < 0.001) and waist circumference (p < 0.001) in men, while age negatively predicted changes in triceps skinfold thickness in women (p < 0.001). Study 2: Fat mass and lean mass were significantly positively associated with bone mineral density (BMD) and fracture risk when adjusted for potential confounders. However, lean mass and not fat mass remained significantly associated with femoral neck BMD (β = 0.49, p <0.001), spine BMD (β = 0.48, p< 0.0001) and hip BMD (β = 0.59, p< 0.0001). Lean mass was also negatively associated with fracture risk (β = -0.19 p =0.04) when both lean and fat mass were in the same model. Study 3: After adjusting for age, body fat, habitual physical activity, tobacco use and season, neither 25(OH)D nor PTH concentrations showed significant associations with having the metabolic syndrome. However, when body fat was replaced with waist circumference there was a weak positive association between 25(OH)D concentration and the metabolic syndrome. No significant association was found between PTH:25(OH)D ratio and the metabolic syndrome. Conclusion This thesis has highlighted that the prevalence of obesity among black South Africans is high particularly among women and urbanization played a significant role in the increasing adiposity of black South Africans in the North West province. Lean mass had a stronger association with bone health in comparison to fat mass in urban black South African women. Low 25(OH)D concentration was not associated with the metabolic syndrome while there was no significant association between PTH and the metabolic syndrome in our black South African women. / PhD (Dietetics), North-West University, Potchefstroom Campus, 2015

Devido às modificações na anatomia e fisiologia do trato gastrointestinal decorrente do procedimento cirúrgico, o pós-operatório da cirurgia bariátrica é acompanhado de significativa perda de peso e melhoras das comorbidades associadas à obesidade, entretanto, também é observado presença de deficiências vitamínico-minerais e de intolerâncias alimentares, principalmente a alimentos fontes de proteína. Por outro lado, os exames bioquímicos de proteína total e albumina não mostram alterações, e é baixa a presença de hipoalbuminemia relatada pela literatura. Assim, o presente trabalho teve como objetivo avaliar o perfil proteico de pacientes submetidos à cirurgia bariátrica pela dosagem dos aminoácidos livres no plasma. Foi realizada avaliação nutricional incluindo antropometria (peso, estatura, circunferência abdominal, cálculo do índice de massa corporal) e composição corporal (bioimpedância elétrica), avaliação da ingestão alimentar (recordatório de 24 horas), dosagens das concentrações séricas de proteína total e albumina e das concentrações plasmáticas de aminoácidos (pelo método de cromatografia líquida de alta eficiência) em 30 mulheres obesas antes e após 3, 6 e 12 meses da cirurgia bariátrica pela técnica de derivação gástrica em Y de Roux. Observou-se redução do peso durante todo o estudo, a maior perda ocorreu no primeiro trimestre no qual também se observou perda de massa magra. Houve redução da ingestão proteica no período pós-operatório, a qual se manteve abaixo dos valores recomendados (<0,8 g/kg/dia). Houve redução das concentrações de proteína total e albumina após 12 meses, entretanto os valores continuaram dentro da normalidade. O perfil aminoacídico mostrou aumento nas concentrações da maioria dos aminoácidos após 3 meses da cirurgia. Após 6 meses da cirurgia, houve redução das concentrações que se manteve até os 12 meses. No final do estudo foi observado que a maior parte dos pacientes apresentou deficiência para a maioria dos aminoácidos, principalmente para os essenciais. A dieta hipocalórica e hipoproteica do pós-operatório, acompanhada da rápida perda de peso inicial, pode promover o catabolismo da musculatura esquelética, aumentando os níveis de aminoácidos circulantes, objetivando suprir a síntese proteica hepática e a gliconeogênese. Assim, observa-se que dosagens de proteína total e albumina são questionáveis na avaliação do perfil proteico de pacientes pós cirurgia bariátrica, visto que, apesar dos valores de normalidade, há uma modificação do perfil de aminoácidos livres no plasma, caracterizado por deficiência para a maioria destes após 12 meses de cirurgia / Due to changes in the anatomy and physiology of the gastrointestinal tract resulting from the surgical procedure, the postoperative period of bariatric surgery is accompanied by a significant weight loss and by improvement of the comorbidities associated with obesity. However, vitamin-mineral deficiencies and food intolerance are also observed, especially regarding foods that are protein sources. On the other hand, biochemical tests for total protein and albumin do not show any changes, and the presence of hypoalbuminemia reported in the literature is low. Thus, the objective of the present study was to assess the patients protein profile submitted to bariatric surgery by measuring free amino acids in plasma. 30 obese women before and 3, 6 and 12 months after bariatric surgery by Roux-en-Y gastric bypass were submitted to nutritional evaluation including anthropometry (weight, height, abdominal circumference, and body mass index calculation) and body composition (bioelectrical impedance), food intake evaluation (24-hour food recall), total protein and albumin serum concentrations and plasma amino acid concentrations by HPLC. Weight reduction was observed throughout the study, with the greatest loss occurring during the first trimester, when a loss of lean mass was also observed. There was a protein reduction intake during the postoperative period, which remained below recommended values (<0.8 g/kg/day). After 12 months, total protein and albumin concentrations were reduced, although their values were still within normal limits. The amino acid profile showed an increase in the concentrations of most amino acids by 3 months after surgery, whereas by 6 months there was a reduction of their concentrations which persisted up to 12 months. At the end of the study, most patients presented deficiencies of most amino acids, especially the essential ones. The low-calorie and low-protein postoperative diet, accompanied by the rapid early weight loss, may promote catabolism of skeletal muscles, increasing the levels of circulating amino acids in order to provide hepatic protein synthesis and neoglucogenesis. Thus, it can be seen that total protein and albumin measurements are questionable for the evaluation of the protein profile of patients after bariatric surgery because, despite normal values, there is a modification of the free amino acid profile in plasma, characterized by deficiency of most of them 12 months after surgery

Devido às modificações na anatomia e fisiologia do trato gastrointestinal decorrente do procedimento cirúrgico, o pós-operatório da cirurgia bariátrica é acompanhado de significativa perda de peso e melhoras das comorbidades associadas à obesidade, entretanto, também é observado presença de deficiências vitamínico-minerais e de intolerâncias alimentares, principalmente a alimentos fontes de proteína. Por outro lado, os exames bioquímicos de proteína total e albumina não mostram alterações, e é baixa a presença de hipoalbuminemia relatada pela literatura. Assim, o presente trabalho teve como objetivo avaliar o perfil proteico de pacientes submetidos à cirurgia bariátrica pela dosagem dos aminoácidos livres no plasma. Foi realizada avaliação nutricional incluindo antropometria (peso, estatura, circunferência abdominal, cálculo do índice de massa corporal) e composição corporal (bioimpedância elétrica), avaliação da ingestão alimentar (recordatório de 24 horas), dosagens das concentrações séricas de proteína total e albumina e das concentrações plasmáticas de aminoácidos (pelo método de cromatografia líquida de alta eficiência) em 30 mulheres obesas antes e após 3, 6 e 12 meses da cirurgia bariátrica pela técnica de derivação gástrica em Y de Roux. Observou-se redução do peso durante todo o estudo, a maior perda ocorreu no primeiro trimestre no qual também se observou perda de massa magra. Houve redução da ingestão proteica no período pós-operatório, a qual se manteve abaixo dos valores recomendados (<0,8 g/kg/dia). Houve redução das concentrações de proteína total e albumina após 12 meses, entretanto os valores continuaram dentro da normalidade. O perfil aminoacídico mostrou aumento nas concentrações da maioria dos aminoácidos após 3 meses da cirurgia. Após 6 meses da cirurgia, houve redução das concentrações que se manteve até os 12 meses. No final do estudo foi observado que a maior parte dos pacientes apresentou deficiência para a maioria dos aminoácidos, principalmente para os essenciais. A dieta hipocalórica e hipoproteica do pós-operatório, acompanhada da rápida perda de peso inicial, pode promover o catabolismo da musculatura esquelética, aumentando os níveis de aminoácidos circulantes, objetivando suprir a síntese proteica hepática e a gliconeogênese. Assim, observa-se que dosagens de proteína total e albumina são questionáveis na avaliação do perfil proteico de pacientes pós cirurgia bariátrica, visto que, apesar dos valores de normalidade, há uma modificação do perfil de aminoácidos livres no plasma, caracterizado por deficiência para a maioria destes após 12 meses de cirurgia / Due to changes in the anatomy and physiology of the gastrointestinal tract resulting from the surgical procedure, the postoperative period of bariatric surgery is accompanied by a significant weight loss and by improvement of the comorbidities associated with obesity. However, vitamin-mineral deficiencies and food intolerance are also observed, especially regarding foods that are protein sources. On the other hand, biochemical tests for total protein and albumin do not show any changes, and the presence of hypoalbuminemia reported in the literature is low. Thus, the objective of the present study was to assess the patients protein profile submitted to bariatric surgery by measuring free amino acids in plasma. 30 obese women before and 3, 6 and 12 months after bariatric surgery by Roux-en-Y gastric bypass were submitted to nutritional evaluation including anthropometry (weight, height, abdominal circumference, and body mass index calculation) and body composition (bioelectrical impedance), food intake evaluation (24-hour food recall), total protein and albumin serum concentrations and plasma amino acid concentrations by HPLC. Weight reduction was observed throughout the study, with the greatest loss occurring during the first trimester, when a loss of lean mass was also observed. There was a protein reduction intake during the postoperative period, which remained below recommended values (<0.8 g/kg/day). After 12 months, total protein and albumin concentrations were reduced, although their values were still within normal limits. The amino acid profile showed an increase in the concentrations of most amino acids by 3 months after surgery, whereas by 6 months there was a reduction of their concentrations which persisted up to 12 months. At the end of the study, most patients presented deficiencies of most amino acids, especially the essential ones. The low-calorie and low-protein postoperative diet, accompanied by the rapid early weight loss, may promote catabolism of skeletal muscles, increasing the levels of circulating amino acids in order to provide hepatic protein synthesis and neoglucogenesis. Thus, it can be seen that total protein and albumin measurements are questionable for the evaluation of the protein profile of patients after bariatric surgery because, despite normal values, there is a modification of the free amino acid profile in plasma, characterized by deficiency of most of them 12 months after surgery

Purpose: The purpose of this study was to determine whether time-restricted feeding (TRF) was an effective dietary strategy for reducing fat mass and preserving fat-free mass while evaluating potential changes in cardiometabolic biomarkers, hormones, muscle performance, and energy and macronutrient intake after eight weeks of aerobic exercise and resistance training in overweight and obese adults. Methods: This study was a randomized, controlled trial. Sedentary, overweight and obese adults (mean ± SD; age: 44.48 ± 7.28 years; BMI: 29.61 ± 2.62 kg/m2; females: 85.71%; males: 14.29%) were randomly assigned to a TRF or normal feeding (NF) dietary strategy group. The TRF group consumed all calories between 1200 and 2000 hours, whereas the NF group ate their typical diet. All groups completed eight weeks of aerobic exercise and supervised resistance training. Body composition, muscle performance, energy and macronutrient intake, physical activity, and physiological variables were assessed week zero and week nine. Results: A total of 21 participants completed the study (NF: n = 10; TRF: n = 11). A mild energy restriction was seen for the TRF (~300 kcal/day, 14.0%) and NF (~250 kcal/d, 11.0%) groups between baseline and week seven. Losses of total body mass were significantly greater for TRF (3.3%) relative to NF (0.2%), of which TRF had significantly greater losses of fat mass (9.0%) compared to NF (3.3%) despite similar reductions in energy intake. Lean mass increased across the intervention for both TRF (0.6%) and NF (1.9%), with no group differences. Conclusion: These data support the use of TRF and concurrent exercise training as a short-term dietary strategy for reducing fat mass and preserving lean mass in overweight and obese adults.

Sarcopenia is a growing health problem in this country as more Americans are living well into old age. It has been thought that a higher protein intake may be related to greater lean muscle mass as well as greater muscular strength and physical functioning. The purpose of this research was to examine protein intake and its relationship to lean body mass and physical functioning in a nationally representative sample of U.S. adults. This research used cross-sectional data from the NHANES 2003-2004 to examine the relationship between protein intake, as an average from two 24h recalls, and dual X-ray absorptiometry (DXA) lean body mass measures. Additionally, these lean body mass measures were examined as predictive of Physical Limitation Score (PLS), an index created from self-reported difficulty in performing basic activities of daily living. Protein intake was examined as total grams of intake, a percentage of total daily energy and as a percent contributed by animal foods. The lean body mass measures used in this analysis included: total lean mass, appendicular lean mass, muscle mass index [lean mass / height (m2)], appendicular lean mass [appendicular lean mass / height (m2)] and percent lean body mass. Questions used to create the self-reported index of functioning, the Physical Limitation Score (PLS), included difficulty in independently: walking ¼ mile, walking up ten stairs without resting, lifting and carrying 10lbs and standing from an armless straight chair. It was found that protein intake significantly, positively predicted lean body mass in select age-gender groups, while more often in men than in women. Total grams of protein intake positively predicted total and appendicular muscle mass index in men ages 19-50 (p-value <0.05), appendicular muscle mass index in men ages 51-70 (p-value 0.038) and percent lean mass in men 71+ years (p-value 0.026). Protein as a percent of energy was a significant, positive predictor of appendicular lean mass in men 19-50 (p-value 0.048), muscle mass index in women 19-50 (p-value 0.007), appendicular muscle mass index in women 19-50 (p-value 0.024) and percent lean mass in men 71+ years (p-value 0.019). Protein as a percent of energy was a significant negative predictor of percent lean mass in older women 71+ years (p-value 0.046). Protein as a percent contributed by animal foods was not a significant predictor of lean mass in any age-gender group. It was also found that Physical Limitation Score (PLS) was surprisingly positively predicted by total and appendicular lean and total and appendicular muscle mass index in nearly all age-gender groups (p-value <0.05) or at least moderately, positively predicted by these (p-value <0.10), meaning that having a greater amount of lean mass predicted greater physical limitation. The only exception was percent lean mass, which was a significant negative predictor of PLS in men and women 60-70 years (p-value <0.05). In this case, a higher percent lean mass was associated with less physical limitation. Additional follow-up analyses revealed that total body fat mass (kg) and percent body fat were significant positive predictors of PLS in most age-gender groups (p-value <0.05), indicating that higher amounts of body fat predicted greater self-reported limitation. Protein expressed as total grams per day or as a percent of total daily energy were generally significant or marginally significant predictors of lean mass in men of all ages but not often in women while protein as a percent contributed by animal foods was not found to be a significant predictor in any age-gender group. Total lean mass, total fat mass and total percent body fat were generally significant positive predictors of physical limitation, calling into question the functional implications of body composition in an older population. Results suggest that in older adults, excess body fat may be a stronger predictor of physical limitation than low lean muscle mass.

No description available.

Introduction Researchers have, for decades, contributed to an increased collective understanding of the physiological demands in cross-country skiing; however, almost all of these studies have used either non-elite subjects and/or performances that emulate cross-country skiing. To establish the physiological demands of cross-country skiing, it is important to relate the investigated physiological variables to the competitive performance of elite skiers. The overall aim of this doctoral thesis was, therefore, to investigate the external validity of physiological test variables to determine the physiological demands in competitive elite cross-country skiing. Methods The subjects in Study I – IV were elite male (I – III) and female (III – IV) cross-country skiers. In all studies, the relationship between test variables (general and ski-specific) and competitive performances (i.e. the results from competitions or the overall ski-ranking points of the International Ski Federation (FIS) for sprint (FISsprint) and distance (FISdist) races) were analysed. Test variables reflecting the subject’s general strength, upper-body and whole-body oxygen uptake, oxygen uptake and work intensity at the lactate threshold, mean upper-body power, lean mass, and maximal double-poling speed were investigated. Results The ability to maintain a high work rate without accumulating lactate is an indicator of distance performance, independent of sex (I, IV). Independent of sex, high oxygen uptake in whole-body and upper-body exercise was important for both sprint (II, IV) and distance (I, IV) performance. The maximal double-poling speed and 60-s double-poling mean power output were indicators of sprint (IV) and distance performance (I), respectively. Lean mass was correlated with distance performance for women (III), whereas correlations were found between lean mass and sprint performance among both male and female skiers (III). Moreover, no correlations between distance performance and test variables were derived from tests of knee-extension peak torque, vertical jumps, or double poling on a ski-ergometer with 20-s and 360-s durations (I), whereas gross efficiency while treadmill roller skiing showed no correlation with either distance or sprint performance in cross-country skiing (IV). Conclusion The results in this thesis show that, depending on discipline and sex, maximal and peak oxygen uptake, work intensity at the lactate threshold, lean mass, double-poling mean power output, and double-poling maximal speed are all externally valid physiological test variables for evaluation of performance capability among elite cross-country skiers; however, to optimally indicate performance capability different test-variable expressions should be used; in general, the absolute expression appears to be a better indicator of competitive sprint performance whereas the influence of body mass should be considered when evaluating competitive distance performance capability of elite cross-country skiers.