Biomedical subjects

D P Heil

Publications and source records attributed to D P Heil.

9 recordsLinked to original sources

PubMed2001

Body mass scaling of projected frontal area in competitive cyclists.

The primary purpose of this study was to evaluate the scaling relationship between body mass (mb) and projected frontal area (AP) of competitive male cyclists whilst allowing statistically for the influence of bicycle geometry. A group of 21 cyclists [mean mb 74.4 (SD 7.2) kg, mean height 1.82 (SD 0.06) m, mean age 23.6 (SD 5.1) years] volunteered to have AP determined from photographs at three trunk angles (TA: 5 degrees, 15 degrees, 25 degrees) for each of three seat-tube angles (STA: 70 degrees, 75 degrees, 80 degrees) using a modified cycle ergometer. Using multiple log-linear regression analysis procedures, the following equation was developed: Body AP (meters squared) = 0.00433 x (STA0.172) x (TA0.0965) x (mb0.762) (r2 = 0.73, SEE = 0.017 m2) (n = 183 images total). This equation indicates that after allowing for the independent influence of STA and TA on AP, AP was proportional to mb raised to the +0.762 power (i.e. Ap is directly proportional to 0.762). The 95% confidence interval for this exponent (0.670-0.854) barely included the theoretical two-thirds value but not the +0.55 value for AP or the +0.32 value for submaximal metabolic power (Ws) of outdoor cycling reported in the literature. Further analysis of wind tunnel data reported in the literature suggests that the coefficient of drag (CD) is proportional to mb raised to the -0.45 power. When combined with the present study findings, it is suggested that the drag area (CD x AP), which should be proportional to Ws at submaximal cycling velocities, is proportional to mb to the +0.312 power (i.e. CD x AP is directly proportional to mb-0.45) x (mb+0.762) = mb+0.312), which is consistent with the +0.32 exponent for Ws in the literature.

Bicycling↗

PubMed2001

Prediction of uphill time-trial bicycling performance in humans with a scaling-derived protocol.

The present study sought to create a scaling-derived cycle ergometer protocol (SDP) that was derived theoretically and would correlate highly with actual uphill time-trial (TT) cycling performance. Local competitive cyclists each completed the SDP (an incremental test to exhaustion) using their own bicycle mounted on a stationary trainer, together with either a short (6.2 km, 2.9% grade; n = 8 men and 5 women) or long-course (12.5 km, 2.7% grade; n = 8 men) uphill TT. Maximal power output (Wmax) and power at the ventilatory threshold (WVT) were determined from the SDP results, as well as maximal oxygen uptake (VO2max), using standard indirect calorimetry procedures. Actual TT speed correlated very highly with both SDP completion time (r = 0.97-0.98) and relative Wmax (watts per kilogram; r = 0.92-0.97) for both uphill TT races. Correlations between TT speed and more demanding measurements (VO2max, WVT) (VO2max, WVT) were generally lower and more variable (r = 0.54-0.97). These results would indicate that two non-laboratory dependent measurements (SDP completion time and relative Wmax) derived from the SDP are valid markers for predicting actual uphill TT performance. This protocol may be useful to cycling coaches and athletes in identifying talented cyclists or for tracking changes in cycling performance outside of the sports science laboratory environment.

Bicycling↗

PubMed1999

Classification of cardiorespiratory fitness without exercise testing.

PURPOSE: We examined the ability of a nonexercise based VO2max, prediction model to classify cardiorespiratory fitness (CRF) in a population of men and women aged 19-79 yr of age (N = 799). METHODS: A VO2max (mL.kg(-1).min(-1)) prediction model was developed in the study group using multiple linear regression from the independent variables age, age2, gender, physical activity status, height, and body mass. The classification accuracy of this model was examined by cross-tabulating age and gender specific quintiles of measured and predicted CRF. RESULTS: Overall classification accuracy of the model was modest (36%); however, 83% of all subjects were either classified correctly or within one quintile of measured CRF. Extreme misclassification (e.g., misclassifying a low fit individual as high fit) was only rarely observed (0.13%). CONCLUSIONS: The present results support the concept that CRF prediction models can be used to reasonably characterize the fitness level of a cohort using data that can be obtained from a questionnaire. Accordingly, predicted CRF values may be useful as an exposure variable in large epidemiologic studies in which exercise testing is not feasible.

Adult↗

PubMed1998

Scaling of submaximal oxygen uptake with body mass and combined mass during uphill treadmill bicycling.

This study examined the scaling relationships of net O2 uptake [V(O2)(net) = V(O2) - resting V(O2)] to body mass (MB) and combined mass (MC = MB + bicycle) during uphill treadmill bicycling. It was hypothesized that V(O2)(net) (l/min) would scale proportionally with MC [i.e., VO2(net) approximately M1.0C] and less than proportionally with MB [i.e., V(O2)(net) approximately MB]. Twenty-five competitive cyclists [73.9 +/- 8.8 and 85.0 +/- 9.0 (SD) kg for MB and MC, respectively] rode their bicycles on a treadmill at 3.46 m/s and grades of 1.7, 3.5, 5.2, and 7.0% while V(O2) was measured. Multiple log-linear regression procedures were applied to the pooled V(O2)(net) data to determine the exponents for MC and MB after statistically controlling for differences in treadmill grade and dynamic friction. The regression models were highly significant (R2 = 0.95, P < 0.001). Exponents for MC (0.99, 95% confidence interval = 0.80-1.18) and MB (0.89, 95% confidence interval = 0.72-1. 07) did not differ significantly from each other or 1.0. It was concluded that the 0.99 MC exponent was due to gravitational resistance, whereas the MB exponent was <1.0 because the bicycles were relatively lighter for heavier cyclists.

Adipose Tissue↗

PubMed1997

The relationship between preferred and optimal positioning during submaximal cycle ergometry.

This study was designed to determine how changes in oxygen uptake (VO2) and heart rate (HR) during submaximal cycle ergometry were determined by changes in cycle geometry and/or lower-limb kinematics. Fourteen trained cyclists [Mean (SD): age, 25.5 (6.4) years; body mass 74.4 (8.8) kg; peak VO2, 4.76 (0.79) 1 x min(-1) peak] were tested at three seat-tube angles (70 degrees, 80 degrees, 90 degrees) at each of three trunk angles (10 degrees, 20 degrees, 30 degrees) using a modified Monark cycle ergometer. All conditions were tested at a power output corresponding to 95% of the VO2 at each subject's ventilatory threshold while pedalling at 90 rpm and using aerodynamic handlebars. Sagittal-view kinematics for the hip, knee, and ankle joints were also recorded for all conditions and for the subjects' preferred positioning on their own bicycles. No combination of seat-tube and trunk angle could be considered optimal since many of the nine conditions elicited statistically similar mean VO2 and HR values. Mean hip angle (HA) was the only kinematic variable that changed consistently across conditions. A regression relationship was not observed between mean VO2 or HR and mean hip angle values (P > 0.45). Significant curvilinear relationships were observed, however, between deltaVO2 (VO2 - minimum VO2) and deltaHA (mean HA - preferred HA) using the data from all subjects (R = 0.45, SEE = 0.13 1 x min(-1)) and using group mean values (R = 0.93, SEE = 0.03 1 x min(-1)). In both cases deltaVO2 minimized at deltaHA = 0, which corresponded to the subjects' preferred HA from their own bicycles. Thus, subjects optimized their VO2 cost at cycle geometries that elicited similar lower-limb kinematics as the preferred geometries from their own bicycles.

Adult↗

PubMed1997

The pressor response to submaximal cycle ergometry while using aerodynamic handlebars.

This study hypothesized that changes in static shoulder loading while using aerobars during submaximal cycle ergometry would elicit a combined static and dynamic pressor response. Seven trained cyclists (mean +/- SD: 22 +/- 3 years, 77 +/- 12 kg, 1.8 +/- 1.1 m) rode a modified Monark cycle ergometer at three inclines (+5 degrees, 0 degree, -5 degrees) for five minutes each using aerobars at a power output (144 +/- 21 W) eliciting 60-65% of each subject's age-predicted HR maximum (120 +/- 4.9 bts.min-1). The positive to negative incline changes were designed to increase the static load experienced by the shoulder musculature. Mean HR, VE, VO2, and rectified EMG for the triceps brachii (TB), anterior (AD) and posterior deltoid muscles were computed over each minute of each condition. All variables exhibited steady-state responses at +5 degrees and 0 degree inclines and nonsteady-state responses at -5 degrees.HR, VO2, and VE correlated highly with EMG from AD (mean r = 0.75-0.79) and TB (mean r = 0.68-0.75) at -5', but only moderately correlated for HR at +5 degrees and 0 degree (mean r = 0.21-0.86). Y-intercepts for HR-VO2 and VE-VO2 relationships shifted positively with increased static load. Thus, static loading of AD and TB may disassociate the HR-VO2 relationship during submaximal cycle ergometry and may be responsible for torso positioning preferences by time-trial cyclists.

Adult↗

PubMed1997

Body mass scaling of peak oxygen uptake in 20- to 79-yr-old adults.

Despite growing evidence in support of the power function ratio (PFR) for body mass (MB) scaling of peak oxygen uptake (VO2PEAK), research literature preferentially reports VO2PEAK values scaled by the simple ratio (SR) method. Theory suggests that VO2PEAK should scale with MB to the 0.67 power (i.e., PFR), while SR scaling assumes an MB exponent of 1.0. This study was designed to determine whether statistically derived MB exponents for a heterogenous sample supported PFR or SR scaling of VO2PEAK. Two hundred thirty women (mean +/- SD: 47.5 +/- 16.8 yr and 64.7 +/- 11.5 kg) and 210 men (45.6 +/- 16.4 yr, 81.77 +/- 12.73 kg) between 20 and 79 yr were evaluated using multiple log-linear regression analysis to determine the MB exponent for VO2PEAK after statistically controlling for age, gender, percent body fat, height, and a self-reported physical activity score. The resulting MB exponent was 0.653 (95% CI: 0.530-0.775) after controlling for all five covariates but increased to 0.756 (0.651-0.862) when height was dropped from the model. Both exponents differed significantly from 1.0 (P < 0.001). These results support the use of PFR scaled VO2PEAK values in adults.

Adult↗

PubMed1995

Cardiorespiratory responses to seat-tube angle variation during steady-state cycling.

The effect of seat-tube angle (STA) variation on oxygen consumption (VO2), heart rate (HR), ventilation (VE), and rating of perceived exertion (RPE) on 25 trained competitive triathletes and cyclists was evaluated during 10-min submaximal tests at each of four STAs (69 degrees, 76 degrees, 83 degrees, 90 degrees). Subjects averaged (mean +/- SD) 26.5 +/- 6.4 yr of age, 68.5 +/- 9.8 kg, 4.26 +/- 0.58 l.min-1 for VO2peak, and 76.2 +/- 1.5 degrees for preferred STA. Tests occurred on a modified cycle ergometer (at each subject's preferred dimensions, except for STA) at a power output that averaged 73% of the subjects' VO2peak and pedaling 90 rpm while using aerodynamic handlebars. Mean VO2, HR, and RPE values at 83 degrees and 90 degrees were significantly lower than values at 69 degrees (3.09, 3.10 vs 3.17 l.min-1; 149.6, 149.9 vs 152.9 bpm; 13.5, 13.5 vs 14.2, respectively; P < 0.05). VE at 83 degrees was significantly lower than VE at 69 degrees (65.2 vs 68.2 l.min-1; P = 0.011). A kinematic analysis found greater hip extension, ankle plantar flexion, and a lower-limb orientation more directly over the crank axis when STA increased. Therefore, only the 69 degrees STA appeared to be a detriment to steady-state cardiorespiratory responses during cycling, whereas the 76 degrees, 83 degrees, and 90 degrees STAs elicited similar cardio-respiratory responses.

Adult↗

PubMed1995

Nonexercise regression models to estimate peak oxygen consumption.

The purpose of this study was to develop a VO2peak prediction model derived from nonexercise (N-EX) based predictors. VO2peak was measured using a walking treadmill protocol with 229 females and 210 males between 20 and 79 yr of age (mean +/- SD: 38.62 +/- 10.36 ml.kg-1.min-1). Subjects were randomly divided into validation (V) (85% of total; N = 374) and cross-validation (CV) (15% of total; N = 65) groups. The V group was used to validate generalized and gender-specific models using stepwise multiple regression procedures with gender, age and age2, percent body fat, and a physical activity code (AC). The generalized ml.kg-1.min-1 (R2 = 0.77, SEE = 4.90 ml.kg-1.min-1, SEE% = 12.7%) and gender-specific (females: R2 = 0.72, SEE = 4.64 ml.kg-1.min-1; males: R2 = 0.72, SEE = 5.02 ml.kg-1.min-1) models were highly accurate relative to N-EX and exercise based models in the literature. Cross-validation procedures were used to evaluate model stability. The generalized model was stable across the total CV group and various CV subsamples (by gender, decade-wide age groups, and AC groups), but not across groups similar in VO2peak. These results suggest that N-EX models can be valid predictors of VO2peak for heterogenous samples.

Adult↗