Changes in selected fitness parameters following six weeks of snowshoe training.

BACKGROUND: Recently, there has been an increase in popularity and participation in the sport of snowshoeing. While the sport has gained considerable recognition, to date there is little or no scientific research regarding training responses to snowshoeing as a form of exercise. Therefore, the purpose of this study was to determine whether snowshoe training could improve fitness measures. A further purpose was to compare responses from a snowshoe training program to a similarly designed run training program. METHODS: This prospective, comparative study was conducted with healthy males and females between the ages of 19 and 24. These subjects were recruited from the University of Vermont population and surrounding community. Following baseline measurements in VO2max, running time to exhaustion (RTE), and anthropometry, 17 subjects (10 snowshoers and 7 runners) participated in a six week conditioning program. Both groups exercised for 30 min at 75-85% age predicted maximum heart rate, 3-4 times per week, for a total of 18 sessions. RESULTS: VO2max improved significantly in both running and snowshoeing groups, 6.3 and 8.5%, respectively. Run time to exhaustion also improved significantly in both groups, 23.3 and 33.5%, respectively. There were no changes in anthropometry for either group. With the exception of RTE, there were no statistically significant differences between groups in any other measurements at baseline. CONCLUSIONS: These results support the acceptability of snowshoeing as a valid means to improve or maintain cardiovascular endurance.

PFK activity in muscle and heart tissue is differentially affected by dietary restriction.

This research examined the effect of dietary restriction on PFK activity (one of the enzymes in the glycolytic pathway) in selected skeletal and heart muscle tissue. Fifty-five Sprague-Dawley female rats were separated into three different groups for 10 weeks of dietary restriction: AL = ad lib fed, MR = weight reduced to 81% of AL and SR = weight reduced to 63% of AL. Gastrocnemius white (GW), plantaris, soleus (S) and heart (H) muscle tissue were dissected out and assayed for PFK activity. PFK activity (mumole/g/min) in GW was 105 +/- 7, 86 +/- 6 and 61 +/- 6 for AL, MR & SR, respectively (AL > MR > SR, P < 0.05). PFK activity in S was 25 +/- 2, 22 +/- 1 and 16 +/- 1 for AL, MR and SR, respectively (AL, MR > SR, P < 0.05). In contrast, PFK activity in H was unaffected (P > 0.05). These data suggest that PFK activity in various muscle tissues is differentially affected during diet-induced weight loss.

A practical equation to predict resting metabolic rate in older men.

The accuracy of previous equations for predicting resting metabolic rate (RMR) in healthy older men is questionable because they are based on limited sample sizes and the absence of cross-validation procedures. The purposes of this study were to (1) examine biological predictors of RMR in healthy older men; (2) develop a practical equation to predict RMR from easily measured variables and examine its accuracy using cross-validation procedures; and (3) test the validity of existing equations in the literature to predict RMR in older men by comparison with measured RMR values. RMR, body composition, anthropometric measurements, leisure time activity (LTA), maximal aerobic power (VO2max), energy intake, and plasma thyroid hormone levels were determined in 89 healthy older men aged 50 to 78 years. Stepwise regression analysis showed that RMR was best predicted by fat-free weight ([FFW] R2 = 85%), free 3,5,3'-triiodothyronine (T3) level (R2 = 1%), and VO2max (R2 = 1%); these variables predicted RMR with a residual error of +/- 30 kcal/d. A practical equation was developed in a randomly selected subsample (N = 61) using easily measured variables as potential predictors, and was successfully cross-validated in a random subsample of older men (N = 28). The pooled equation to predict RMR is as follows: RMR (in kilocalories per day) = 9.7 (weight in kilograms) - 6.1 (chest skinfold thickness in millimeters) - 1.8 (age in years) + 0.1 (leisure time activity [LTA] in kilocalories per day) + 1,060. These variables accounted for 76% (R2) of the variation, and predicted RMR with a residual error of +/- 42 kcal/d.(ABSTRACT TRUNCATED AT 250 WORDS)

A practical equation to predict resting metabolic rate in older females.

OBJECTIVE: To develop a practical and accurate age-specific equation for predicting resting metabolic rate (RMR) in older women and, thereafter, to cross-validate existing equations for predicting RMR in older females. DESIGN: Cross-sectional validation study. SETTING: General Clinical Research Center. PARTICIPANTS: A convenience sample of 75 healthy older women (age 50-81) free of significant cardiovascular or any other non-cardiac disease that may affect cardiovascular function or metabolic rate. MEASUREMENTS: All 75 volunteers were characterized for resting metabolic rate (RMR), body composition, anthropometrics, physical activity, and energy intake. RESULTS: A practical equation for predicting RMR in older women using easily measured variables was: [RMR (kcal/d) = 7.8 (weight,kg) + 4.7 (standing height, cm) -39.5 (menopausal status; 1-3) + 143.5]. These variables accounted for 59% (R2) of the variation in RMR and predicted RMR within +/- 66 kcal/d. When five previously published equations were applied to our sample of older women to predict RMR, individual predicted values deviated by -31% to 20% from the measured value. CONCLUSION: We offer a practical equation to predict RMR in healthy older women based on a measure of body weight, standing height, and menopausal status.

Resting energy metabolism and cardiovascular disease risk in resistance-trained and aerobically trained males.

The objectives of this study were (1) to examine differences in resting metabolic rate (RMR) and cardiovascular risk factors among aerobically trained (n = 36), resistance-trained (n = 18), and untrained (n = 42) young males; and (2) to investigate the influence of body composition, dietary intake, and VO2max as possible modulators of differences in cardiovascular risk among groups. Results showed that RMR, adjusted for differences in fat-free weight (FFW), was 5% higher in aerobically trained males compared with resistance-trained males (P < .01), and 10% higher than that in untrained males (P < .01). Plasma levels of cholesterol and low-density lipoprotein cholesterol (LDL-C) were comparable between resistance-trained and aerobically trained males, but were lower (P < .05) than those in untrained males. (The percent intake of dietary fat was related to plasma cholesterol [r = .32, P < .01] and LDL-C [r = .30, P < .01].) When compared with untrained males, fasting triglyceride (TG) levels were 39% and 43% lower (P < .01) in resistance-trained and aerobically trained males, respectively. When compared with untrained males, the fasting insulin to glucose ratio (I/G) was 45% and 53% lower (P < .01) in resistance- and aerobically trained males, respectively. Mean arterial pressure (MAP) was 7% lower (P < .01) in aerobically trained compared with untrained males. Statistical control for differences in percent body fat or percent intake of dietary fat diminished the differences among the groups for plasma lipids, blood pressure, and the I/G ratio. We conclude that aerobically trained and resistance-trained males have higher resting energy requirements independent of FFW compared with untrained males. Aerobically trained and resistance-trained young males have comparable and favorable cardiovascular disease risk profiles compared with untrained males, and this appears to be related to their low level of adiposity and low intake of dietary fat.

Thyroid function, energy balance, body composition and organ growth in protein-deficient chicks.

Protein-deficient diets (17, 10, 6.5 or 3% protein) and a 24% control diet were fed to growing chicks. A control group was pair-fed daily with each deficient group. Energy intake was lower in the 6.5 and 3% protein groups than in the other groups. However, weight gain, bone growth and feed conversion efficiency were lower with 10% protein or less. Relative thyroid weights were unaffected by dietary protein. Plasma T3 (3,5,3'-triiodothyronine) levels were significantly higher in all deficient groups, whereas plasma T4 (thyroxine) was lower. Plasma rT3 (reverse T3) was unaffected by the protein deficiencies, suggesting that enhanced conversion of T4 to T3 rather than to rT3 had occurred. Hepatic alpha-glycerol-3-phosphate dehydrogenase (alpha-GP) shuttle activity increased markedly in protein-deficient chicks. Efficiency of energy utilization was unaltered in chicks fed 17 or 10% protein but was higher in chicks fed 6.5 and 3% protein than in controls. All deficient chicks had more fat and less protein and water in the tissues. The lower feed conversion efficiency therefore represents almost entirely a shift in body composition toward fat and does not reflect a loss of energy as heat. We conclude that elevations in plasma T3 and in thyroid-controlled alpha-GP shuttle activity, although sensitive indicators of protein deficiencies, are not good predictors of altered thermogenic activity in protein-deficient chicks.

Regression of brown adipose tissue mitochondrial function and structure in neonatal goats.

Rapidly regressing perirenal brown adipose tissue (BAT) of neonatal goats was studied to correlate changes in mitochondrial metabolism and thermogenic capacity with changes in mitochondrial structure. The alpha-glycerophosphate shuttle activity of perirenal BAT mitochondria declined 60% from birth to 6 days of age. Oxygen consumption and thermogenic capacity measured by ion conductance peaked at birth and declined to low levels at 6 days. Sample electron micrographs of perirenal BAT showed intact electron-dense mitochondria with many cristae and little matrix area at 2 days. However, by 6 days the mitochondria were very relaxed with large matrix area, few cristae, and observable degradation. These results indicate that the morphological changes exhibited by rapidly regressing goat's perirenal BAT in the 1st wk postpartum are accompanied by dramatic alterations in BAT mitochondrial function.

Altered brown adipose tissue mitochondrial function in neonates born to rats overfed foods of various protein content.

On day 3 of pregnancy, 20 female Sprague-Dawley rats were randomly divided into four groups and fed either a powdered, control diet containing 27% casein (control) or "cafeteria" diets of low (7%, LP), normal (26%, NP) or high (35%, HP) protein content throughout gestation. Maternal gross energy intake was significantly increased 35% in each of the cafeteria-fed groups compared to control. At birth, mean body weight of the offspring in each diet group was not significantly different, whereas brown adipose tissue (BAT) weight and mitochondrial function (unrestricted minus GDP-inhibited anion conductance) were significantly decreased in LP offspring and increased in NP and HP offspring when compared to controls. Maternal diet composition, therefore, can alter neonatal BAT mitochondrial function and, perhaps, thermogenic capacity independent of total energy intake during pregnancy.

Mechanisms of thermogenesis induced by low protein diets.

Weanling (22-day-old) rats fed a low protein (8% casein) diet consumed the same amount of energy as controls (22% casein diet), but intake corrected for body size (kJ/kg0.75) was increased in the former group. Weight gain and the efficiency of gain (g gain/MJ) were markedly reduced in low protein fed rats. Resting oxygen consumption (VO2) was elevated by 15% in the low protein group but this difference was completely abolished by beta-adrenergic blockade with propranolol. Interscapular brown adipose tissue (BAT) mass, protein content, mitochondrial yield and GDP binding were increased in low protein fed rats but mitochondrial alpha-glycophosphate shuttle activity of BAT was unaltered, although shuttle activity was elevated in liver mitochondria. Plasma triiodothyronine levels were increased by 64% in the low protein group, whereas insulin levels were markedly reduced in spite of normal blood glucose levels. Resting VO2 and BAT mass were also increased in older (55-day-old) rats fed the low protein diet, but the changes were smaller than in weanling rats. These data suggest that the decreased metabolic efficiency seen in rats fed protein deficient diets involves sympathetic activation of BAT, and is therefore similar to the thermogenic responses seen in cold adapted and cafeteria-fed animals.

Energy balance and mitochondrial function in liver and brown fat of rats fed "cafeteria" diets of varying protein content.

Rats fed "cafeteria" diets with low (7%, LP) normal (23%, NP) or high (33%, HP) protein contents showed increases in metabolizable energy intake (kJ/kg 0.75, 23-41%) and in energy expenditure (36%) compared to controls fed stock diet (27% protein). The high metabolic rates were inhibited by beta-adrenergic blockade with propranolol. All rats fed cafeteria diets deposited more fat than controls, but the LP diet depressed growth, and these animals also showed the lowest energetic efficiency. Brown adipose tissue (BAT) mass and protein content were increased in all groups fed cafeteria diets, but the largest changes occurred in LP-fed animals, and the smallest in the HP group. Hepatic mitochondrial alpha-glycerophosphate shuttle activity and plasma triiodothyronine levels were elevated twofold in rats fed LP cafeteria diet compared to controls, but the other cafeteria diet groups showed little or no changes, and shuttle activity in BAT was not affected by any of the diets. Blood glucose and plasma insulin levels were similar for control, NP and HP animals, whereas glucose levels were slightly lower and insulin levels were very much lower in the rats fed LP cafeteria diet.

The effects of pre- and postweaning dietary protein levels of mitochondrial metabolism in developing liver and interscapular brown adipose tissue (IBAT) in rats.

Isoenergetic diets containing casein:carbohydrate:fat, 22:59:10% (control protein, CP), or 8:73:10% (low protein, LP), were fed to female rats during gestation and lactation and to offspring postweaning. Control fed rats were pair-fed to the LP-fed group. In the LP-fed group, body and liver weights were similar at birth but decreased at 10, 21, and 42 days, while intercapsular brown adipose tissue (IBAT) weight decreased from birth to 10 and 21 days but increased at 42 days compared to controls. Hepatic mitochondrial oxygen consumption (OC) with pyruvate + malate as substrate was similar at 21 and 42 days, whereas OC in state 3 and 4 with succinate was decreased at 42 days, only in the LP-fed group. In IBAT, OC was similar in each group at each age. In the LP-fed group, hepatic glycerolphosphate (GP) shuttle activity was the same as in controls at birth but increased progressively from 10 to 21 and 42 days, whereas malate-aspartate (M-A) shuttle activity was not substantially changed during development. In IBAT, shuttle activities were similar in both groups during development with M-A shuttle activity increased in the LP-fed group at 21 days. Serum triiodothyronine (T3) levels in the LP-fed group were increased at 10 and 42 days but decreased at 21 days after birth. These results suggest a role for both pre- and postweaning diet composition as a regulator of hepatic metabolism during development. The deficit in IBAT weight in the LP-fed group during early postnatal development indicates a decreased capacity for heat production in the neonate caused by maternal protein undernutrition.

Influence of diet composition on serum triiodothyronine (T3) concentration, hepatic mitochondrial metabolism and shuttle system activity in rats.

Two experiments were conducted to determine if variations in diet composition sufficient to alter circulating triiodothyronine (T3) concentration would influence hepatic mitochondrial metabolism. In experiment 1, mitochondrial respiration and the activity of succinate dehydrogenase (SDH), cytochrome oxidase (CO) and alpha glycerophosphate dehydrogenase (m alpha-GPD) were measured in 42-day-old male rats fed diets containing casein/carbohydrate/fat: 8/73/10% (low protein), 22/59/10% (control protein), and 45/36/10% (high protein) for 3 weeks. When compared to control, serum T3 was increased 2-3 times in the low and decreased 19% in the high protein-fed groups. Mitochondria isolated from low protein-fed rats consumed less oxygen in both state 4 and state 3 with succinate as substrate when compared to control or high protein fed rats. However, ADP/O and respiratory control (RC) ratios were similar in all groups. Activity of SDH and CO was decreased only in low protein-fed rats. M alpha-GPD activity was increased in the low and decreased in the high protein fed-rats. In experiment 2, alpha-glycerophosphate shuttle activity was increased 2-3 fold and malate-aspartate shuttle activity decreased 60% in intact mitochondria isolated from low protein-fed rats when compared to rats pair-fed control diet. These results suggest a role for diet composition as a regulator of hepatic intermediary metabolism mediated by thyroid hormones.