Relation of bone mineral density and content to mineral content and density of the fat-free mass.

Differences in the mineral fraction of the fat-free mass (M(FFM)) and in the density of the FFM (D(FFM)) are often inferred from measures of bone mineral content (BMC) or bone mineral density (BMD). We studied the relation of BMC and BMD to the M(FFM) and D(FFM) in a heterogeneous sample of 216 young men (n = 115) and women (n = 101), which included whites (n = 155) and blacks (n = 61) and collegiate athletes ( n = 132) and nonathletes (n = 84). Whole body BMC and BMD were determined by dual-energy X-ray absorptiometry (DXA; Hologic QDR-1000W, enhanced whole body analysis software, version 5.71). FFM was estimated using a four-component model from measures of body density by hydrostatic weighing, body water by deuterium dilution, and bone mineral by DXA. There was no significant relation of BMD to M(FFM) (r = 0.01) or D(FFM) (r = -0.06) or of BMC to M(FFM) (r = -0.11) and a significant, weak negative relation of BMC to D(FFM) (r = -0.14, P = 0.04) in all subjects. Significant low to moderate relationships of BMD or BMC to M(FFM) or D(FFM) were found within some gender-race-athletic status subgroups or when the effects of gender, race, and athletic status were held constant using multiple regression, but BMD and BMC explained only 10-17% of the variance in M(FFM) and 0-2% of the variance in D(FFM) in addition to that explained by the demographic variables. We conclude that there is not a significant positive relation of BMD and BMC to M(FFM) or D(FFM) in young adults and that BMC and BMD should not be used to infer differences in M(FFM) or D(FFM).

Use of air displacement plethysmography for estimating body fat in a four-component model.

PURPOSE: To compare measurements of body density (D(b)) obtained from air displacement plethysmography (AP) and hydrostatic weighing (HW) and to determine the accuracy of substituting D(b) via AP (D(b)-AP) for D(b) via HW (D(b)-HW) in estimating body fatness (%Fat(4C)) and the composition and density of the fat-free mass (Dffm) from a four-component model (fat, mineral, water, and protein). METHODS: D(b) was measured in 50 young adults using AP and HW. Total body water via deuterium dilution, bone mineral content via dual-energy x-ray absorptiometry, and D(b) were used to estimate %Fat(4C). RESULTS: D(b)-AP and D(b)-HW were highly correlated (r = 0.89, SEE = 0.008 g x mL(-1)), but D(b)-AP (1.065 +/- 0.003 g x mL(-1)) was significantly higher (P < 0.05) than D(b)-HW (1.058 +/- 0.003 g x mL(-1)), resulting in a mean difference of 2.8%fat. Differences between %Fat(4C-AP) (17.8 +/- 1.2%) and %Fat(4C-HW) (19.3 +/- 1.2%) were significant (P < 0.05), but the SD of the differences (2.3%) was low. When D(b)-AP was used in a four-component model in place of D(b)-HW, the calculated Dffm was significantly higher (1.109 +/- 0.002 vs 1.105 +/- 0.002 g x mL(-1)) based on a higher (P < 0.05) protein fraction (22.0 +/- 0.4% vs 20.6 +/- 0.4%) and lower (P < 0.05) water (71.1 +/- 0.4% vs 72.4 +/- 0.4%) and mineral fractions (7.0 +/- 0.1% vs 7.1 +/- 0.1%). CONCLUSIONS: AP yields a higher D(b) than HW and may not be a valid method for measuring D(b) or estimating %fat using densitometry. However, due to relatively small bias and low individual error, D(b)-AP is an acceptable substitute for D(b)-HW when estimating %fat with a four-component model in young adults.

Body composition estimates from multicomponent models using BIA to determine body water.

PURPOSE: The purpose of this study was to compare estimates of body fat (%BF) from three- and four-component models with total body water (TBW) determined by single-frequency bioelectrical impedance analysis (BIA; %BF3C-BIA and %BF4C-BIA) to %BF estimates from densitometry (%BF2C-D) and from three- and four-component models with TBW determined using deuterium dilution (%BF3C-D2O and %BF4C-D2O), the criterion methods. METHODS: Measures of body density by hydrostatic weighing, TBW by BIA and D2O dilution, and bone mineral by dual energy x-ray absorptiometry (DXA) were obtained in 40 men and 93 women, 18-42 yr. TBW was estimated from BIA resistance (RJL analyzer) using an equation developed and cross-validated in two independent samples. Body fat was estimated using the three-component model of Siri (1961) and a four-component model modified from Lohman (1986). RESULTS: There was a strong relation and no significant difference between TBW estimated by BIA and D2O [r = 0.94, SEE = 2.4; xDiff = 0.0 +/- 2.4 L (SD), P > 0.05]. There were strong relations between methods for estimating %BF, with deviations from %BF4C-D2O (errors) for %BF3C-BIA [r = 0.99, SEE = 2.4% BF, xDiff = -0.4 +/- 2.4% BF (SD)] and %BF4C-BIA [r = 0.99, SEE = 2.3% BF, xDiff = 0.2 +/- 2.3% BF (SD)] being nonsignificant (P > 0.05) although greater than for %BF3C-D2O [r = 1.00, SEE = 0.5% BF, xDiff = -0.6 +/- 0.5% BF (SD)], and comparable or slightly worse than for %BF2C-D [r = 0.99, SEE = 2.3% BF, xDiff = 0.4 +/- 2.3% BF (SD)]. CONCLUSIONS: We conclude that because estimates of %BF from multicomponent models with TBW estimated from BIA are not more accurate than from body density alone using a two-component model, estimates of %BF from three- and four-component models using TBWBIA are not acceptable substitutes for estimates from the same models using TBWD2O.

Acoustic startle eyeblink response after acute exercise.

The acoustic startle eyeblink response (ASER) is a useful probe for investigating central nervous system activity associated with emotional responses to aversive and appetitive stimuli. Though the ASER is sensitive to change in emotional arousal, the effect of acute physical exertion on ASER has not been reported. We examined changes in ASER amplitude and latency in 26 healthy young men (24+/-5 yr) after 20 min of cycling at light and hard intensities (40% and 75% VO2peak) and after 20 min of quiet rest. Mixed model ANCOVA, controlling precondition scores, indicated no effects for ASER amplitude or latency in either sedentary or active participants (p>.10). Our findings indicate that possible effects of acute exercise on potentiated startle or ASER responses elicited by positive or negative foreground stimuli should not be expected to be confounded by an altered baseline acoustic startle eyeblink response when measured in healthy young men.

Muscularity and the density of the fat-free mass in athletes.

The purpose of this study was to use estimates of body composition from a four-component model to determine whether the density of the fat-free mass (D(FFM)) is affected by muscularity or musculoskeletal development in a heterogenous group of athletes and nonathletes. Measures of body density by hydrostatic weighing, body water by deuterium dilution, bone mineral by whole body dual-energy X-ray absorptiometry (DXA), total body skeletal muscle estimated from DXA, and musculoskeletal development as measured by the mesomorphy rating from the Heath-Carter anthropometric somatotype were obtained in 111 collegiate athletes (67 men and 44 women) and 61 nonathletes (24 men and 37 women). In the entire group, D(FFM) varied from 1.075 to 1.127 g/cm3 and was strongly related to the water and protein fractions of the fat-free mass (FFM; r = -0.96 and 0.89) and moderately related to the mineral fraction of the FFM (r = 0.65). Skeletal muscle (%FFM) varied from 40 to 68%, and mesomorphy varied from 1.6 to 9.6, but neither was significantly related to D(FFM) (r = 0.11 and -0.14) or to the difference between percent fat estimated from the four-component model and from densitometry (r = 0.09 and -0.16). We conclude that, in a heterogeneous group of young adult athletes and nonathletes, D(FFM) and the accuracy of estimates of body composition from body density using the Siri equation are not related to muscularity or musculoskeletal development. Athletes in selected sports may have systematic deviations in D(FFM) from the value of 1.1 g/cm3 assumed in the Siri equation, resulting in group mean errors in estimation of percent fat from densitometry of 2-5% body mass, but the cause of these deviations is complex and not simply a reflection of differences in muscularity or musculoskeletal development.

Muscle activation and the slow component rise in oxygen uptake during cycling.

PURPOSE: During constant-rate high-intensity exercise, a steady state for oxygen uptake (VO2) is not achieved and, after the initial rapid increase, VO2 continues to increase slowly. The mechanism underlying the slow-component rise in VO2 during high-intensity exercise is unknown. It has been hypothesized that increased muscle use may be a contributing factor, but only limited electromyograph (EMG) data are available supporting this hypothesis. The purpose of this study was to determine whether there is an association between the VO2 slow component and muscle use assessed by contrast shifts in magnetic resonance images (magnetic resonance imaging (MRI)). METHODS: The VO2 slow component was measured in 16 subjects during two 15-min bouts of cycling performed at high and low intensities. EMG and MRI transverse relaxation times (T2) were obtained after 3 and 15 min to determine muscle activity at each intensity. RESULTS: Low-intensity cycling produced no VO2 slow component, and no increases in muscle activity, except for a small increase (P < 0.05) in the T2 of the vastus lateralis. During high-intensity cycling, VO2, T2 of the vastus lateralis, rectus femoris and whole leg, and EMG activity and median power frequency of the vastus lateralis rose significantly (P < 0.05) from 3 to 15 min. Percent increases in VO2 and muscle T2 were related during high-intensity cycling (r = 0.63), but not during low-intensity cycling (r = 0.00). CONCLUSION: We conclude that increased muscle use is in part responsible for the slow component rise in oxygen uptake. The results support the hypothesis that during constant-rate exercise at intensities above lactate threshold, progressively greater use of fast-twitch motor units increases energy demand and causes concomitant progressive increases in VO2 and lactate.

Effects of diet and exercise on the density and composition of the fat-free mass in obese women.

PURPOSE: The purpose of this study was to determine whether the density (D(FFM)) and composition of the fat-free mass (FFM) and the accuracy of estimates of body composition from body density (%Fat(d)) are affected by diet and exercise. METHODS: Twenty-nine obese women (body mass index (BMI) = 25.0-43.7 kg x m(-2) and %Fat(d) = 35.7-47.1%) were assigned to one of three groups: diet only (DO, N = 9); diet and aerobic exercise (DE, N = 9); or control (C, N = 11). Measures of body density by hydrostatic weighing, body water by deuterium dilution, and bone mineral by whole-body dual-energy x-ray absorptiometry, and estimates of body composition from body density and from a four-component model were obtained before and after a 16-wk diet and exercise intervention. RESULTS: Mean (+/- SD) changes in body mass were -7.2 +/- 7.4, -3.9 +/- 3.3, and +1.2 +/- 2.8 kg for the DO, DE, and C, respectively. The density and composition of the FFM did not change significantly (P > 0.05) in any of the groups. Individual changes in D(FFM) (-0.011 to +0.011 g x mL(-1)), and differences between changes in %Fat estimated using a four-component model and %Fat(d) (-2.1 to +2.7% body mass) were not related to changes in body mass (r = -0.08). Individual changes in D(FFM) were most strongly related to changes in water fraction (r = -0.95) and protein fraction (r = +0.88), and were unrelated to changes in the mineral fraction (r = +0.04) of the FFM. CONCLUSIONS: We conclude that in obese women, the density and composition of the FFM are unaltered and densitometry correctly assesses group mean changes in body composition with moderate weight loss induced by diet or diet and aerobic exercise. However, individual deviations in D(FFM) from the assumed value of 1.1 g x mL(-1) are substantial, and a multi-component model in which body water is measured is needed to accurately assess individual body composition changes resulting from diet and exercise.

Impact of bone mineral estimates on percent fat estimates from a four-component model.

PURPOSE: The primary purpose of this study was to determine the impact of bone mineral content (BMC) from QDR 1000/W and DPX-L dual-energy x-ray absorptiometers (DXA(QDR) and DXA(DPX-L) on percent fat (%fat) estimates from a four-component model. A secondary purpose was to test the accuracy of %fat estimates from DXA(QDR) and DXA(DPX-L) using %fat estimates from a four-component model as the criterion. METHODS: Percent fat, fat mass, and fat-free mass (FFM) were determined from DXA(QDR) and DXA(DPX-L) and from a four-component model based on measures of body density from underwater weighing, body water from deuterium dilution, and BMC from DXA(QDR) (4C(QDR)) or DXA(DPX-L) (4C(DPX-L)) in young men (N = 14) and women (N = 10). RESULTS: BMC was significantly lower using DXA(QDR) compared with DXA(DPX-L) (approximately 11%), resulting in slightly lower estimates of %fat and fat mass and slightly higher estimates of FFM from 4C(QDR) than 4C(DPX-L). Although estimates of %fat, fat mass, and FFM from DXA(QDR) and DXA(DPX-L) were not different than those from a four-component model, there was considerable individual variability between methods. Furthermore, %fat from DXA(QDR) was lower than %fat from 4C(DPX-L). CONCLUSIONS: We conclude that using BMC from different DXA instruments has a minimal impact on %fat, fat mass, and FFM estimates from a four-component model. The large variability in %fat estimates between the two DXA instruments and those from a four-component model does not support DXA as a criterion method of body composition. Further studies involving larger sample sizes and specific population groups are needed to assess the validity of body composition measurements from DXA.

Body-composition changes with diet and exercise in obese women: a comparison of estimates from clinical methods and a 4-component model.

BACKGROUND: Most methods available to clinicians for estimating body-composition changes have been validated against estimates from densitometry, based on a 2-component (fat mass and fat-free mass) model. OBJECTIVE: Estimates of changes in percentage body fat (%BF) from dual-energy X-ray absorptiometry (DXA), skinfold thicknesses (SFTs), bioelectrical impedance analysis (BIA), and body mass index (BMI; in kg/m2) were compared with estimates from a 4-component (fat, water, mineral, and protein) model (%BFd,w,m), a more accurate method. DESIGN: Determinations of body density from hydrostatic weighing, body water from deuterium dilution, bone mineral and %BF from whole-body DXA, resistance from BIA, and anthropometric measures were made in 27 obese women (BMI: 31.1 +/- 4.9) assigned to 1 of 3 groups: control (C; n = 9), diet only (DO; n = 9), or diet plus aerobic exercise (DE; n = 9). RESULTS: After the 16-wk intervention, changes in body mass (BM) averaged 0.5 +/- 2.0, -7.2 +/- 7.4, and -4.0 +/- 3.3 kg and changes in %BFd,w,m averaged 2.1 +/- 1.0%, -1.2 +/- 1.4%, and -2.4 +/- 1.6% in the C, DO, and DE groups, respectively. Compared with changes in %BFd,w,m, the errors (SD of bias) for estimates of changes in %BF by DXA, BIA, SFTs, and BMI were similar (range: +/-2.0-2.4% of BM). BIA, SFTs, and BMI provided unbiased estimates of decreases in %BFd,w,m, but DXA overestimated decreases in %BF in the DO and DE groups. CONCLUSIONS: DXA, BIA, SFTs, and BMI are comparably accurate for evaluating body-composition changes induced by diet and exercise interventions; however, small changes in %BF may not be accurately detected by these clinical methods.

In vivo validation of whole body composition estimates from dual-energy X-ray absorptiometry.

We validated whole body composition estimates from dual-energy X-ray absorptiometry (DEXA) against estimates from a four-component model to determine whether accuracy is affected by gender, race, athletic status, or musculoskeletal development in young adults. Measurements of body density by hydrostatic weighing, body water by deuterium dilution, and bone mineral by whole body DEXA were obtained in 172 young men (n = 91) and women (n = 81). Estimates of body fat (%Fat) from DEXA (%FatDEXA) were highly correlated with estimates of body fat from the four-component model [body density, total body water, and total body mineral (%Fatd,w,m); r = 0.94, standard error of the estimante (SEE) = 2.8% body mass (BM)] with no significant difference between methods [mean of the difference +/- SD of the difference = -0.4 +/- 2.9 (SD) % BM, P = 0.10] in women and men. On the basis of the comparison with %Fatd,w,m, estimates of %FatDEXA were slightly more accurate than those from body density (r = 0.91, SEE = 3.4%; mean of the difference +/- SD of the difference = -1.2 +/- 3.4% BM). Differences between %FatDEXA and %Fatd,w,m were weakly related to body thickness, as reflected by BMI (r = -0.34), and to the percentage of water in the fat-free mass (r = -0.51), but were not affected by race, athletic status, or musculoskeletal development. We conclude that body composition estimates from DEXA are accurate compared with those from a four-component model in young adults who vary in gender, race, athletic status, body size, musculoskeletal development, and body fatness.

One-mile run-walk performance in young men and women: role of anaerobic metabolism.

The aim of this study was to evaluate the importance of anaerobic metabolism as a determinant of individual differences in performance of a 1-mile run-walk (MRW). Anaerobic capacity, percentage of anaerobic capacity used during the MRW, percentage of energy used during the MRW that was supplied through anaerobic processes, aerobic metabolic determinants of distance running performance, and MRW time were measured in 26 male and 29 female young adult nonathletes. Anaerobic processes averaged 7-8% of the energy used during the MRW. In multiple regression analyses, anaerobic capacity, and a linear combination of all three anaerobic variables contributed significantly to the prediction of MRW with the effects of gender and VO2 peak held constant, but the additional variance accounted for by the anaerobic variables was relatively small (2-7%). In conclusion, anaerobic metabolism supplies only a small portion of the energy used during the MRW, and anaerobic capacity and metabolism during the MRW do not confound its interpretation as an indicator of maximal aerobic power in a heterogeneous group of young men and women of moderate fitness level.

Anaerobic capacity and muscle activation during horizontal and uphill running.

Anaerobic capacity as measured by the maximal or peak oxygen deficit is greater during uphill than during horizontal running. The objective of this study was to determine whether the greater peak oxygen deficit determined during uphill compared with horizontal running is related to greater muscle volume or mass activated in the lower extremity. The peak oxygen deficit in 12 subjects was determined during supramaximal treadmill running at 0 and 10% grade. Exercise-induced contrast shifts in magnetic resonance images were obtained before and after exercise and used to determine the percentage of muscle volume activated. The mean peak oxygen deficit determined for uphill running [2.96 +/- 0.63 (SD) liters or 49 +/- 6 ml/kg] was significantly greater (P < 0.05) than for horizontal running (2.45 +/- 0.51 liters or 41 +/- 7 ml/kg) by 21%. The mean percentage of muscle volume activated for uphill running [73.1 +/- 7. 4% (SD)] was significantly greater (P < 0.05) than for horizontal running (67.0 +/- 8.3%) by 9%. The differences in peak oxygen deficit (liters) between uphill and horizontal running were significantly related (y = 8.05 x 10(-4)x + 0.35; r = 0.63, SE of estimate = 0.29 liter, P < 0.05) to the differences in the active muscle volume (cm3) in the lower extremity. We conclude that the higher peak oxygen deficit during uphill compared with horizontal running is due in part to increased mass of skeletal muscle activated in the lower extremity.

Increased finger arterial blood pressure after exercise detraining in women with parental hypertension: autonomic tasks.

The effects of exercise detraining on resting finger arterial blood pressure (BP), the carotid-cardiac vagal baroreflex, and BP and heart rate (HR) responses to mental arithmetic and forehead cold exposure were studied in young (19 +/- 1.1 years) normotensive women with parental history of hypertension. Following 8 weeks of aerobic exercise for 25 min, 3 days week-1 at an intensity of 60% VO2peak, subjects ceased training for 6-8 weeks. After detraining, VO2peak (mL kg-1 min-1) was reduced by 11.5% (41.1 +/- 6.9 to 36.4 +/- 4.8) coincident with an approximately equal to 10% increase in submaximal exercise heart rate. Responses to the laboratory tasks were then compared. Detraining was accompanied by increases (P < 0.05) in resting systolic (SBP) (113.6 +/- 8.9 to 121.2 +/- 9.0), diastolic (DBP) (63.0 +/- 8.4 to 68.3 +/- 6.8), and mean arterial (MAP) (78.7 +/- 8.4 to 84.2 +/- 7.3) BP (mmHg). None of the above changes occurred in sedentary matched-control subjects. Systolic blood pressure was elevated during forehead cold exposure and MAP was elevated during mental arithmetic after detraining, but the rates of response and recovery for SBP, DBP and MAP were not altered by detraining. Despite higher submaximal exercise HR after detraining, HR responses to autonomic challenges, including the carotid-cardiac vagal baroreflex, were unchanged between training and detraining. Our results indicate that exercise detraining increases resting finger arterial BP in young normotensive women at risk for hypertension with no effects on the rate of response or recovery of heart rate and BP during autonomic tasks known to elicit sympathetic and carotid-cardiac vagal activities in this population. The use of auscultatory brachial artery pressures in a similar study of women diagnosed with hypertension will clarify the clinical meaning of our findings.

Metabolic determinants of the age-related improvement in one-mile run/walk performance in youth.

We examined the metabolic determinants of the age-related improvement in 1-mile run/walk (MRW) performance in boys and girls. Treadmill VO2peak (ml.kg-1.min-1), running economy (VO2 in ml.kg-1.min-1 at 8 km.h-1; VO2econ), and %VO2peak used during a simulated MRW were determined in 92 boys and 53 girls, 7-17 yr of age. Simple linear regression analyses indicated that MRW time decreased 0.52 min.y-1, VO2econ decreased 1.0 ml.kg-1.min-1.y-1, %VO2peak increased 1.5%.y-1, and no significant change occurred in VO2peak. Multiple linear regression analyses indicated that the increase in %VO2peak used during the run accounted for about 42% of the decrease in MRW time with age. With the effects of VO2peak and %VO2peak held constant, the improvement in VO2econ accounted for an additional 31% of the age-related decrease in MRW time. We conclude that the age-related improvement in MRW performance in youth is explained primarily by an increase in the %VO2peak used during the MRW and improvement in VO2econ. Age-related changes in MRW time should not be used to infer changes in VO2peak.

Lower extremity muscle activation during horizontal and uphill running.

To provide more comprehensive information on the extent and pattern of muscle activation during running, we determined lower extremity muscle activation by using exercise-induced contrast shifts in magnetic resonance (MR) images during horizontal and uphill high-intensity (115% of peak oxygen uptake) running to exhaustion (2.0-3.9 min) in 12 young women. The mean percentage of muscle volume activated in the right lower extremity was significantly (P <0.05) greater during uphill (73 +/- 7%) than during horizontal (67 +/- 8%) running. The percentage of 13 individual muscles or groups activated varied from 41 to 90% during horizontal running and from 44 to 83% during uphill running. During horizontal running, the muscles or groups most activated were the adductors (90 +/- 5%), semitendinosus (86 +/- 13%), gracilis (76 +/- 20%), biceps femoris (76 +/- 12%), and semimembranosus (75 +/- 12%). During uphill running, the muscles most activated were the adductors (83 +/- 8%), biceps femoris (79 +/- 7%), gluteal group (79 +/- 11%), gastrocnemius (76 +/- 15%), and vastus group (75 +/- 13%). Compared with horizontal running, uphill running required considerably greater activation of the vastus group (23%) and soleus (14%) and less activation of the rectus femoris (29%), gracilis (18%), and semitendinosus (17%). We conclude that during high-intensity horizontal and uphill running to exhaustion, lasting 2-3 min, muscles of the lower extremity are not maximally activated, suggesting there is a limit to the extent to which additional muscle mass recruitment can be utilized to meet the demand for force and energy. Greater total muscle activation during exhaustive uphill than during horizontal running is achieved through an altered pattern of muscle activation that involves increased use of some muscles and less use of others.

Effects of concentric and eccentric training on muscle strength, cross-sectional area, and neural activation.

We compared the effects of concentric (Con) and eccentric (Ecc) isokinetic training on quadriceps muscle strength, cross-sectional area, and neural activation. Women (age 20.0 +/- 0.5 yr) randomly assigned to Con training (CTG; n = 16), Ecc training (ETG; n = 19), and control (CG; n = 19) groups were tested before and after 10 wk of unilateral Con or Ecc knee-extension training. Average torque measured during Con and Ecc maximal voluntary knee extensions increased 18.4 and 12.8% for CTG, 6.8 and 36.2% for ETG, and 4.7 and -1.7% for CG, respectively. Increases by CTG and ETG were greater than for CG (P < 0.05). For CTG, the increase was greater when measured with Con than with Ecc testing. For ETG, the increase was greater when measured with Ecc than with Con testing. The increase by ETG with Ecc testing was greater than the increase by CTG with Con testing. Corresponding changes in the integrated voltage from an electromyogram measured during strength testing were 21.7 and 20.0% for CTG, 7.1 and 16.7% for ETG, and -8.0 and -9.1% for CG. Quadriceps cross-sectional area measured by magnetic resonance imaging (sum of 7 slices) increased more in ETG (6.6%) than in CTG (5.0%) (P < 0.05). We conclude that Ecc is more effective than Con isokinetic training for developing strength in Ecc isokinetic muscle actions and that Con is more effective than Ecc isokinetic training for developing strength in Con isokinetic muscle actions. Gains in strength consequent to Con and Ecc training are highly dependent on the muscle action used for training and testing. Muscle hypertrophy and neural adaptations contribute to strength increases consequent to both Con and Ecc training.

Density of the fat-free mass and estimates of body composition in male weight trainers.

The purpose of this study was to determine whether the assumed density and composition of the fat-free mass (FFM) and estimates of percent fat (%Fat) from body density by use of the Siri equation (%Fatd) are valid in weight trainers with high musculoskeletal development. Measures of body density by underwater weighing (Db), body water by deuterium dilution, and bone mineral by whole body dual-energy X-ray absorptiometry were obtained in young white men: 14 weight trainers with high musculoskeletal development and 14 non-weight-training controls with average musculoskeletal development. %Fatd was significantly higher (P < or = 0.05) than %Fat estimated from body density, water, and mineral (%Fatd,w,m) by use of a four-component model in weight trainers (17.3 +/- 4.6 vs. 13.2 +/- 5.1%) but not in controls (14.8 +/- 3.1 vs. 14.2 +/- 3.6%). The greater discrepancy between %Fatd and %Fatd,w,m was explained by lower density of fat-free mass (Dffm) in weight trainers (1.089 +/- 0.005 g/ml) than in controls (1.099 +/- 0.007 g/ml). The lower Dffm in the weight trainers was due to higher water (74.8 +/- 1.2 vs. 72.6 +/- 20%) and lower mineral (5.3 +/- 0.6 vs. 5.9 +/- 0.4%) and protein (19.9 +/- 1.4 vs. 21.5 +/- 1.9%) fractions of the FFM. We conclude that, in young white men with high musculoskeletal development, Dffm is lower than the assumed value of 1.1 g/ml and %Fat is overestimated from Db by use of the Siri equation.

Effect of the slow-component rise in oxygen uptake on VO2max.

During constant-rate high-intensity (CRHI) exercise lasting longer than 3 min, VO2 has been reported to exceed VO2max measured with a traditional graded exercise test (GXT). This could be because VO2max was not achieved on the GXT or because the factors responsible for the slow-component rise in VO2 alter VO2max. The objective of this study was to test the hypothesis that the slow-component rise in VO2 measured during CRHI running leads to a total VO2 that exceeds VO2max measured during a running GXT. VO2max was determined in eight highly trained individuals using data collected from five grade-incremented, treadmill-running GXT. Each subject demonstrated a definitive plateau of VO2 as a function of exercise intensity. Three VO2max values based on different approaches for representing the VO2max plateau were obtained. Subjects also completed two exhaustive CRHI bouts of treadmill running lasting 7-13 min at speeds estimated from the ACSM equation to elicit an average of 99 +/- 5% VO2max. The mean (+/- SD) VO2peak determined during the CRHI runs (4.17 +/- 0.9 l.min-1) was not different form or less than the three VO2max values (4.19-4.32 +/- 0.09 l.min-1). We conclude that in highly trained individuals, the slow-component rise in VO2 during CRHI treadmill running does not lead to a total VO2 that exceeds the VO2max measured during a running graded exercise test.

A generalized equation for prediction of VO2peak from 1-mile run/walk performance.

The purpose of this study was to develop and cross-validate a generalized equation for predicting VO2peak from 1-mile run/walk (MRW) time and demographic variables in youth and young adults. Data for 753 males and females 8-25 yr of age were divided into validation (N = 495) and cross-validation (N = 258) samples. The validation sample was used to develop a multiple regression equation for predicting treadmill VO2peak (ml.kg-1.min-1) from gender (0 = F, 1 = M), age (yr), body mass index (kg.m-2; BMI) and MRW time (min). The multiple correlation (R) and standard error of estimate (SEE) were: R = 0.71, SEE = 4.8 ml.kg-1.min-1. The accuracy of this equation was confirmed when applied to the cross-validation sample. The regression equation for the total sample was: VO2peak = -8.41 (MRW) + 0.34 (MRW)2 + 0.21 (Age x Gender) -0.84 (BMI) + 108.94, R = 0.72, SEE = 4.8 ml.kg-1.min-1. We conclude that the generalized equation provides valid estimates of VO2peak in youth and young adults. The equation should be useful for educators, clinicians, and researchers who would like to interpret results of the MRW test in terms of VO2peak.

Autonomic responses of women with parental hypertension. Effects of physical activity and fitness.

We studied the moderating effects of cardiorespiratory fitness and physical activity on heart rate and blood pressure responses to psychophysiological stressors and the carotid-cardiac baroreflex in young normotensive women with a parental history of hypertension (n = 31). Testing occurred during the follicular menstrual phase. Subjects were divided into high versus moderate (46.6 +/- 6.5 versus 35.9 +/- 1.9 mL.kg-1.min-1) VO2peak and high versus moderate (1217.7 +/- 98.4 versus 1015.5 +/- 49.4 J.kg-1.wk-1) physical activity groups. The groups did not differ in heart rate or blood pressure responses to mental arithmetic or the cold-face test. However, the highly fit women had longer maximal R-R intervals compared with the moderately fit women when the carotid-cardiac baroreflex was stimulated by negative pressures applied to the neck during resting conditions (P < .01). The carotid-cardiac baroreflex was attenuated during mental arithmetic compared with rest in both the moderately fit and moderately active women but not in the highly fit and highly active groups. We find no evidence that aerobic fitness reduces sympathetic responses to laboratory stressors in young women with parental hypertension. Our findings are consistent with greater parasympathetic tone during sympathetic challenge for the highly fit and highly active subjects. Clarification of autonomic balance during carotid baroreflex stimulation at rest and during sympathetic challenge after exercise training would provide important information regarding mechanisms that regulate cardiovascular responses to autonomic challenge in women at risk for hypertension.