Ventilatory Threshold Related to V̇O 2 reserve, Heart Rate Reserve, and Rating of Perceived Exertion in a Large Varied Sample.

PURPOSE: ACSM guidelines state that aerobic exercise intensity should be 30%/40% to 89% V̇O 2 reserve (V̇O 2 R) or heart rate reserve (HRR). Determining the proper intensity within this range is the "art" of exercise prescription, often relying on rating of perceived exertion (RPE) as the adjunctive intensity modulator. Current guidelines do not consider the use of ventilatory threshold (VT) due to the need for specialized equipment and methodological issues. The purpose of this investigation was to evaluate VT related to V̇O 2peak , V̇O 2 R, HRR, and RPE across the full spectrum of very low to very high V̇O 2peak values. METHODS: Eight hundred and sixty-three records of exercise tests were retrospectively examined. Data were stratified for V̇O 2peak , activity level, age, test modality, and sex. RESULTS: When stratified for V̇O 2peak , V̇O 2 at VT (V̇O 2 vt) had a lower mean value of ~14 mL·kg -1 ·min -1 in the lowest fit, rose gradually until median V̇O 2peak , and rose steeply thereafter. When graphed relative to V̇O 2peak , V̇O 2 vt as a percentage of V̇O 2 R (VT%V̇O 2 R) resembled a U-shaped curve, with a nadir ~43% V̇O 2 R at V̇O 2peak ~40 mL·kg -1 ·min -1 . Average VT%V̇O 2 R increased to ~75% in groups with the lowest or highest V̇O 2peak . There was a large variance in the value of VT at all V̇O 2peak levels. Mean RPE at VT was 12.5 ± 0.93, regardless of V̇O 2peak . CONCLUSIONS: Given the relationship of VT as the transition from moderate- to higher-intensity exercise, these data may help the understanding of aerobic exercise prescription in persons across the spectrum of V̇O 2peak values.

Metabolic Demand of Hiking in Wildland Firefighting.

INTRODUCTION: The objective of this study was to document characteristics of hiking during wildland firefighter (WLFF) training and wildfire suppression. For the first time, the overall physical demands during wildland firefighting were evaluated in the field using global positioning systems coupled with wireless physiological monitoring and load carriage prediction models. METHODS: Male (n=116) and female (n=15) interagency hotshot crew and type II WLFFs on wildfires volunteered for this direct observation study. Participants' heart rate, internal temperature, speed, and elevation gain were monitored throughout training and during wildfire suppression. The Pandolf and Santee equations were used to predict metabolic rate to estimate oxygen consumption of uphill and downhill hiking. RESULTS: Equipment weight varied by crew type (type II: 24±9 kg and interagency hotshot crew: 28±6 kg; P<0.05). Grade of terrain was steepest during training hikes, and ingress hikes were statistically different from egress and training hikes (ingress: 4±9%, shift: 4±9%, egress: 1±8%, training hikes: 10±9%; P<0.01). Estimated oxygen consumption was highest during ingress hikes and was significantly different from all other hike types on fire assignments (ingress: 22±12, shift: 19±12, egress: 19±12 mL·kg-1·min-1; P=0.01). Oxygen consumption was higher during training hikes (34±14 mL·kg-1·min-1) than during job-related hikes (P<0.01). CONCLUSIONS: The greatest metabolic demand during wildfire assignments occurred during ingress hikes. On average, this was close to the estimated metabolic demand of the job qualification arduous pack test. However, greater metabolic demand occurred for periods during both shift (on the job) and training hikes. These data quantify the demands associated with actual wildland performance of WLFFs and can help define future work capacity testing and training procedures.

Current considerations related to physiological differences between the sexes and physical employment standards.

The use of physical employment standards (PES) has helped ensure that workers have the physical attributes necessary to complete their jobs in a safe and efficient manner. However, PES used in the selection processes have not always reflected the critical physical requirements of the job tasks. Women generally have smaller anthropometric stature than men, less muscle mass, and therefore less strength, power, and endurance, particularly in the upper body. Nonetheless, these attributes in themselves are not valid grounds for exclusion from employment in physically demanding occupations. Selection standards based upon size or strength, irrespective of the job requirements, have resulted in the barring of capable women from physically demanding jobs, claims of gender bias, and costly litigations. To ensure all individuals are provided with equal access to employment, accurate characterization of the critical physical requirements of the job is paramount. This paper summarizes the existing research related to disparities between the sexes that contribute to sex differences in job performance in physically demanding occupations including physical and legal factors. Strategies for mitigating these differences in the setting of PES and the meeting of minimum employment standards are discussed. Where available, injury rates for women and men in physically demanding occupations are presented and the etiology considered. Finally, areas for further research are identified.

Exogenous carbohydrate spares muscle glycogen in men and women during 10 h of exercise.

PURPOSE: The purpose of the study was to evaluate the effects of carbohydrate (CHO) supplementation on whole-body and net muscle substrate use during 10 h of discontinuous exercise, simulating occupational settings in men and women. METHODOLOGY: Recreationally trained subjects (N = 7 males, N = 6 females) performed a graded exercise test on a treadmill (TM) and cycle ergometer (CE) to determine ventilatory threshold (VT) and V O2peak. In a double-blind, randomized crossover design, subjects received either CHO [20% maltodextrin (0.6 g.kg FFM.h)] or flavored placebo (PLA) drink each hour across 10 h of exercise. Exercise intensity was 71.3 +/- 3% and 72.4 +/- 4% VT for TM and CE, respectively. Hourly exercise included 9 min of upper-body ergometery, 19 min of cycling, and 20 min of treadmill walking, with a 1-min transition between modes, followed by a 10-min rest and feeding period. The protocol was selected to simulate arduous occupational settings. Vastus lateralis biopsies were obtained before and after exercise. Expired gases were collected every other hour to establish average rates of whole-body CHO and fat oxidation. Blood glucose (BG) was measured continuously. RESULTS: Whole-body CHO oxidation was maintained during CHO trial compared with the PLA trial. Net muscle glycogen use was 52% higher for the PLA trial (176.0 +/- 16.7, 117.0 +/- 20.9 and 164.5 +/- 11.0, 133.8 +/- 10.9 mmol.kg w.w. for PLA and CHO, respectively, P < 0.05). There were no significant sex-specific differences in glycogen use, whole-body substrate oxidation, or BG values. CONCLUSION: The ingestion of CHO during long-duration exercise decreases net muscle glycogen use while better maintaining whole-body carbohydrate oxidation, and potentially increasing performance in field settings. There are limited differences in sex-specific substrate oxidation.

Supplemental feedings increase self-selected work output during wildfire suppression.

PURPOSE: The purpose of this study was to determine the impact of supplemental feeding strategies on self-selected activity during wildland fire suppression. METHODS: Seventy-six wildland firefighters were studied in three experiments for three fire seasons. During the first two seasons, subjects consumed, in addition to their sack lunch, 1) liquid carbohydrate (CHO) (200 mL.h, 20% CHO (40 g.h, 160 kcal.h)) or placebo (PLA) every hour, or 2) liquid CHO (200 mL.h, 20% CHO (40 g.h, 160 kcal.h) every even hour and solid CHO (25 g of CHO, 10 g of protein, 2 g of fat, and 160 kcal.h) every odd hour, or PLA, using counterbalanced crossover designs. During the third season, subjects consumed their sack lunch halfway through their workday, or shift food items of approximately 150-400 kcal at 90-min intervals after breakfast in a randomized crossover design (isocaloric intake, 1534+/-265 kcal per workday). Work output was monitored using CSA and MiniMitter actigraphy units. RESULTS: During the liquid CHO trials, subjects consuming CHO demonstrated significantly higher average activity counts throughout the day compared with PLA (50,262+/-36,560 and 40,159+/-35,969 counts per hour for 12 h for the CHO and PLA trials, respectively; P<0.05). For the liquid+solid CHO trials, subjects consuming CHO demonstrated higher average activity counts per minute 2 h before lunch and the last 4 h of the workday compared with PLA (P<0.05). For the sack lunch and shift food trials, subjects consuming shift foods demonstrated higher average counts per minute during the final 2 h compared with those consuming sack lunch (521+/-421 vs 366+/-249 counts per minute during 2 h; P<0.05). CONCLUSION: Liquid and/or solid supplemental CHO and regular feedings increased self-selected work rates during wildland fire suppression, particularly during the latter hours of the workday.

Effects of high intensity / low volume and low intensity / high volume isokinetic resistance exercise on postexercise glucose tolerance.

The purpose of this study was to determine the effects of high intensity/ low volume (HILV) and low intensity/high volume (LIHV) isokinetic resistance exercise on postexercise glucose tolerance. Subjects (n = 10) participated in a counterbalanced, randomized design of 2 separate isokinetic resistance exercise trials (HILV and LIHV) of reciprocal concentric knee flexion and knee extension in a fasted state. Each bout was followed by a 45-minute oral glucose tolerance test (OGTT; 1.8 g.kg fat free mass(-1)). Blood samples were obtained every 15 minutes to determine glucose and insulin concentrations. There was no difference in total work between the 2 trials (p = 0.229). Blood glucose was significantly higher at all time points compared with time 0 following the LIHV trial (p < 0.05). Following the HILV trial, blood glucose was significantly elevated at 15 and 30 minutes (p < 0.05), but returned to resting values by 45 minutes. Insulin concentration was significantly elevated following both trials at all time points (p < 0.05). Blood glucose and insulin were significantly higher following the LIHV at 30 and 45 minutes compared with the HILV trial (p < 0.05). These results demonstrate that although the total work output was similar across trials, high intensity muscle contraction is associated with an enhanced normalization of glucose homeostasis following a large postexercise oral glucose feed.

Substrate oxidation during incremental arm and leg exercise in men and women matched for ventilatory threshold.

The aim of this study was to determine the variations in substrate utilization between men and women matched for ventilatory threshold (Tvent) during incremental arm cranking and leg cycling exercise at 70, 85, 100 and 115% of the mode-specific Tvent. Recreationally active men (n=12) and women (n=10) with similar values for percentage of peak oxygen consumption at Tvent participated in the study. Ventilatory equivalence, excess CO2 and modified V-slope methods were used concurrently to determine Tvent. The participants performed 5 min of exercise at each of 70, 85, 100 and 115% Tvent during both arm cranking and leg cycling exercise. The females were tested during the early follicular phase for all trials. A two-way mixed-design analysis of variance was performed to test for differences between the sexes. When carbohydrate and fat oxidation were expressed relative to total fat-free mass, carbohydrate oxidation during arm cranking and leg cycling was significantly higher in men than women at each percentage of Tvent. In contrast, women showed significantly higher fat oxidation across intensities during both arm cranking and leg cycling. Our results suggest that when substrate utilization is expressed relative to total fat-free mass, women appear to maintain a higher rate of fat and lower rate of carbohydrate oxidation than men during both incremental arm cranking and leg cycling exercise relative to Tvent.

Hydration status and water turnover of dogsled drivers during an endurance sled dog event in the arctic.

OBJECTIVES: To determine changes in common urinary markers of hydration maintained by the drivers (mushers) during a wilderness endurance event in the arctic and to determine water turnover in this select group of individuals. STUDY DESIGN: During this descriptive study, data was systematically collected on hydration, water turnover, changes in resting and exercise heart rate, fatigue and rating of perceived exertion during an arduous dogsled race in the arctic. METHODS: Sixteen mushers were recruited for the study, 13 of whom completed the entire race. At five different checkpoints along the 1049-mile trail (symbolic distance), urine was collected. Urine osmolality (U(osm)) was determined using freezing point depression. Urine specific gravity (U(sg)) was determined using a hand-held refractometer. Water turnover was measured in 5 mushers from rates of deuterium (2H2O) elimination (rH2O). Prior to the start of the race, and at five checkpoints along the trail, a resting heart rate, fatigue rating scale and a rating of perceived exertion (RPE), were collected. RESULTS: Out of the 13 subjects that completed the event, four of the mushers had a U(sg) > or = 1.030 (mean 1.023 +/- 0.007) at some point during the event. Ten had a urine osmolality > or = 900 mOsm L(-1) at some point during the event, with an average U(osm) of 868 +/- 277 mOsm L(-1) over the duration of the event. Water turnover demonstrated that rH2O averaged 2.85 +/- 1.18 ml kg(-1) day(-1) (range 2.03 -4.60) over the duration of the event. Resting heart rate increased significantly over the course of the race. The RPE was related to the overall fatigue rating scale. CONCLUSIONS: These data demonstrate that the majority of mushers studied showed signs of dehydration based on common urinary markers during the long-distance dogsled race. The dehydration appears to have had an influence on the resting heart rate, overall fatigue and the rating of perceived exertion during the race.

Development of upper body power in junior cross-country skiers.

With the advent of the ski-skating technique, upper body power has increasingly been shown to be a major factor in cross-country skiing success. The purpose of this study was to evaluate 4 commonly used training methods (weight, circuit, rollerboard, and ski-specific training) for the development of upper body power (UBP) in junior cross-country skiers. Fifty-eight adolescent cross-country skiers (Boys: n = 29, age = 16.0 +/- 1.2 y and Girls: n = 29, age = 15.5 +/- 1.5 y) were assigned to one of the UBP training methods for a 10-week training program. Fourteen cross-country runners served as controls (boys: n = 7, age = 15.8 +/- 1.7 y; girls: n = 7, age = 14.9 +/- 1.3 y). Skiers were evaluated pre- and post-training for upper body strength (UBS) using a 10 repetition maximum (RM) rollerboard test, for UBP using a double-poling ergometer and for upper body endurance (UBE) with a 3-km, arms-only, rollerski endurance time trial. Competitive race results were collected during the winters before and after training as were all training data. Only the rollerboard training group improved significantly greater than the control group (p < 0.05) in UBP and UBS. Improvements in UBP, UPS, and UBE were significantly related (r = 0.545, 0.303, and 0.407, respectively) to improvements in competitive performance. These data suggest that training using a rollerboard with 5-12RM and explosive speed is more effective in developing UBP than other common training methods for adolescent cross-country skiers. The practical importance of these data was verified by the significant relationships between improvements in UBP, UBS, and UBE related to improvements in competitive race performance.

Heart rate versus %VO2max: age, sex, race, initial fitness, and training response--HERITAGE.

PURPOSE: In the HERITAGE Family Study, heart rate (HR) associated with various percentages of maximal oxygen intake (VO2max) was used to prescribe exercise intensity. When fitness improved, HR at the same power output (PO) decreased, and PO was increased to produce the prescribed HR. Although we assumed that subjects were again working at the same %VO2max, there were no studies with a large heterogeneous population to determine whether this was correct. METHODS: Therefore, 653 subjects with complete data were classified by age, sex, race, initial VO2max, and VO2max response after 20 wk of training. RESULTS: All groups had a significant increase in VO2max and a significant decrease in HR at the same absolute PO after training but no difference in HR at the same relative intensity. CONCLUSIONS: Training does not affect HR at a given %VO2max in a heterogeneous population of men and women, blacks and whites aged 17-65 yr with different initial VO2max values and different responses to training.

Major gene effects on exercise ventilatory threshold: the HERITAGE Family Study.

This study investigates whether there are major gene effects on oxygen uptake at the ventilatory threshold (VO(2VT)) and the VO(2VT) maximal oxygen uptake (VT%VO(2 max)), at baseline and in response to 20 wk of exercise training by using data on 336 whites and 160 blacks. Segregation analysis was performed on the residuals of VO(2VT) and VT%VO(2 max). In whites, there was strong evidence of a major gene, with 3 and 2% of the sample in the upper distribution, that accounted for 52 and 43% of the variance in baseline VO(2VT) and VT%VO(2 max), respectively. There were no genotype-specific covariate effects (sex, age, weight, fat mass, and fat-free mass). The segregation results were inconclusive for the training response in whites, and for the baseline and training response in blacks, probably due to insufficient power because of reduced sample sizes or smaller gene effect or both. The strength of the genetic evidence for VO(2VT) and VT%VO(2 max) suggests that these traits should be further investigated for potential relations with specific candidate genes, if they can be identified, and explored through a genome-wide scan.