Similar Work Rate Research Articles

Analysis of electrical stimulation and voluntary muscle contraction on skeletal muscle oxygen uptake and mitochondrial recovery using near-infrared spectroscopy.

This investigation was to compare differences in skeletal muscle oxygen consumption ([Formula: see text]) and mitochondrial recovery between voluntary (VOL) and electrically stimulated (ES) plantarflexion contractions. Twelve men and women (26 ± 4.0years; 171.8 ± 5.1cm; 74.0 ± 13.7kg) were seated in a chair with their right knee fully extended and right foot secured to a force transducer. ES electrodes and a near-infrared spectroscopy device were placed on the gastrocnemius. Participants performed ES plantarflexion contractions across a range of stimulation intensities at frequencies of 1 and 2Hz and similar VOL contractions. Cuff occlusion occurred immediately following each series of contractions to measure [Formula: see text]. A standardized mitochondrial function assessment protocol was also performed to calculate K-constants between work-matched ES and VOL contractions. For mitochondrial assessments, there were no significant differences between ES and VOL rate constants (2.03 ± 0.98 vs. 1.25 ± 1.35min-1, p = 0.266). ES resulted in a significantly greater workrate-[Formula: see text] slope at 1Hz (0.007 ± 0.007 vs. 0.001 ± 0.002% [Formula: see text]/s/N, p = 0.014) and 2Hz (0.010 ± 0.010 vs. 0.001 ± 0.001% [Formula: see text]/s/N, p = 0.012), as well as a significantly greater workrate-[Formula: see text] Y-intercept at 2Hz (1.603 ± 1.513 vs. 0.556 ± 0.564% [Formula: see text]/s, p = 0.035) but not 1Hz (0.579 ± 0.448 vs. 0.442 ± 0.357% mV̇O2/s, p = 0.535) when compared to VOL. ES results in a significantly greater [Formula: see text] at similar work rates compared to VOL, however, the mitochondrial recovery rate constants were similar. The greater mVO2 with ES may partially contribute to the increased rate of fatigue during ES exercise in individuals with muscle paralysis.

Respiratory and Perceptual Responses to High-Intensity Interval Exercise in Obese Adults.

Although high-intensity interval exercise (HIIE) has emerged as an attractive alternative to continuous exercise (CE), the effects of HIIE on ventilatory constraints and dyspnea on exertion have not been studied in obese adults, and thus, tolerability of HIIE in obese adults is unknown. The purpose of this study was to examine differences in respiratory and perceptual responses between HIIE and CE in nonobese and obese adults. Ten nonobese (5 men; 24.1 ± 6.2 yr; body mass index, 23.0 ± 1.3 kg·m-2) and 10 obese (5 men; 24.2 ± 3.8 yr; body mass index, 37 ± 4.6 kg·m-2) adults participated in this study. Respiratory and perceptual responses were assessed during HIIE (eight 30-s intervals at 80% maximal work rate, with 45-s recovery periods) and two 6-min sessions of CE, completed below and above ventilatory threshold (Vth). Despite similar work rate, HIIE was completed at a higher relative intensity in obese when compared with nonobese participants (68.8% ± 9.4% vs 58.9% ± 5.6% maximal oxygen uptake, respectively; P = 0.01). Expiratory flow limitation and/or dynamic hyperinflation was present during HIIE in 50% of the obese but in none of the nonobese participants. Ratings of perceived breathlessness were highest during HIIE (5.3 ± 2.4), followed by CEaboveVth (2.5 ± 1.6), and CEbelowVth (0.9 ± 0.7; P < 0.05) in obese participants. Unpleasantness associated with breathlessness was higher in obese (4.2 ± 3.0) when compared with nonobese participants (0.6 ± 1.3; P = 0.005) during HIIE. HIIE, when prescribed relative to maximal work rate, is associated with greater ventilatory constraints and dyspnea on exertion when compared with CE in obese adults. CE may be more tolerable when compared with HIIE for obese adults.

Sex-differences In Exercising Hemodynamics: Role Of Exercising Muscle Mass

Sex-differences in O2 transport include O2 content (CaO2) and quantity of muscle mass. PURPOSE: To determine their consequences on exercising hemodynamics with large (e.g., 2-leg cycling (BIKE)) vs. small (e.g., 1-leg knee extension (KE)) muscle mass. METHODS: Healthy young subjects (4M, 3W) completed BIKE and KE exercise tests. The femoral artery and vein were catheterized to measure leg blood flow (Q), CaO2, and mean arterial pressure (MAP). Vascular conductance (VC), O2 delivery, and leg O2 uptake (VO2) were calculated. Measures were normalized to the right leg (BIKE) or quadriceps (KE) lean mass. Whole body VO2 was measured with a metabolic cart. Men and women were compared at similar and maximal work rates. RESULTS: Body mass was greater in men (M: 80±6 vs. W: 59±12 kg, p=0.03). Although quadriceps mass (3.3±0.2 vs. 2.0±0.3 kg, p<0.001) and CaO2 were lower, women had a higher mass-specific Q, VC (p=0.054), O2 delivery, and leg VO2 to maintain whole body VO2 during similar KE (Table 1). These differences were maintained during maximal KE, at which women tended to achieve a higher mass-specific work rate (21±2 vs. 25±3 W·kg-1, p=0.10). They were also apparent during similar BIKE despite a lower leg lean mass in women (8.7±0.3 vs. 5.3±0.7 kg, p<0.001). However, the differences were no longer present during maximal BIKE when mass-specific work rate was similar (21±2 vs. 20±2 W·kg-1, p=0.70) and whole body VO2 was lower in women. CONCLUSION: These findings highlight a greater hemodynamic capacity for women to overcome differences in CaO2 and maintain whole body VO2 at similar work rates during exercise. They also implicate the quantity of exercising muscle in facilitating the greater hemodynamic capacity and mass-specific work rate during maximal exercise with a small but not large muscle mass. Support: The Swedish National Centre for Research in Sports, Ministerio de Educacion y Ciencia of Spain, Dr. Manuel Morales Foundation, NSERCTable 1: Exercising hemodynamics (*p<0.05, **p<0.01, ***p<0.001 men vs. women)

The noninvasive simultaneous measurement of tissue oxygenation and microvascular hemodynamics during incremental handgrip exercise.

Limb blood flow increases linearly with exercise intensity; however, invasive measurements of muscle microvascular blood flow during incremental exercise have demonstrated submaximal plateaus. We tested the hypotheses that 1) brachial artery blood flow (Q̇BA) would increase with increasing exercise intensity until task failure, 2) blood flow index of the flexor digitorum superficialis (BFIFDS) measured noninvasively via diffuse correlation spectroscopy would plateau at a submaximal work rate, and 3) muscle oxygenation characteristics (total-[heme], deoxy-[heme], and percentage saturation) measured noninvasively with near-infrared spectroscopy would demonstrate a plateau at a similar work rate as BFIFDS. Sixteen subjects (23.3 ± 3.9 yr, 170.8 ± 1.9 cm, 72.8 ± 3.4 kg) participated in this study. Peak power (Ppeak) was determined for each subject (1.8 ± 0.4 W) via an incremental handgrip exercise test. Q̇BA, BFIFDS, total-[heme], deoxy-[heme], and percentage saturation were measured during each stage of the exercise test. On a subsequent testing day, muscle activation measurements of the FDS (RMSFDS) were collected during each stage of an identical incremental handgrip exercise test via electromyography from a subset of subjects ( n = 7). Q̇BA increased with exercise intensity until the final work rate transition ( P < 0.05). No increases in BFIFDS or muscle oxygenation characteristics were observed at exercise intensities greater than 51.5 ± 22.9% of Ppeak. No submaximal plateau in RMSFDS was observed. Whereas muscle activation of the FDS increased until task failure, noninvasively measured indices of perfusive and diffusive muscle microvascular oxygen delivery demonstrated submaximal plateaus. NEW & NOTEWORTHY Invasive measurements of muscle microvascular blood flow during incremental exercise have demonstrated submaximal plateaus. We demonstrate that indices of perfusive and diffusive microvascular oxygen transport to skeletal muscle, measured completely noninvasively, plateau at submaximal work rates during incremental exercise, even though limb blood flow and muscle recruitment continued to increase.

Impact of Wheel Size on Energy Expenditure during Mountain Bike Trail Riding

This study examined the energy expenditure during mountain bike trail rides on a 26-inch wheel (26er) compared to a 29-inch wheel (29er). Thirteen experienced bikers (four women, nine men, age=33.0±10.1 yrs), completed similar 6.7km trail rides on a 26er and 29er. GPS was used to measure distance and speed during each ride. Energy expenditure was determined by measuring oxygen consumption. Compared to the 26er, the 29er rides took less total time (24.2±3.2 vs. 25.5±3.5 minutes, p=0.015), hence faster speeds (4.7±0.6 vs. 4.4±0.6 m•s-1, p=0.022), lower average heart rates (155.0±19.2 vs. 162.2±16.8 bpm, p=0.047), and lower total calories (263.3±34.3 vs. 290.7± 36.9 kcals, p=0.001). Work rates represented by the rate of oxygen consumption (ml O2•min-1, p=0.65) were not different. At similar work rates, riders apparently gained a mechanical advantage on the 29ers allowing for 5% lower riding times and heart-rates, 6.8% faster speeds, and a 9.4% reduction in the total caloric expenditure for a standardized trail ride.

VO2 Kinetics during Different Forms of Cycling Exercise on Land and in Water

Background: It is generally assumed that the physical properties of water improve aerobic me- tabolism by O 2 utilization of the working muscle particular if a great muscle mass is recruited. This study investigated the changes in VO 2 (VO 2 -work rate relationship; ∆ VO 2 / ∆ WR) during increasing work rates in different exercise conditions in water immersed exercise and on land based exercise. Methods: In order to identify possible differences in VO 2 required for a given work rate twelve trained cyclists performed four incremental exercise tests. The tests comprised whole body work and leg work, both in water and on land and were conducted on the same, electromagneti- cally braked whole body ergometer. Results: The ∆ VO 2 / ∆ WR curves were found to be similar in the four exercise conditions reach- ing from 11.9 to 12.4 ml·W -1 during water immersed exercise and 12.6 to 12.7 ml·W -1 dur- ing land based exercise respectively. When coupling arms with leg exercise the ∆ VO 2 / ∆ WR curves shift upwards at similar work rates indicating a higher oxygen demand for an enlarged muscle mass. The extra O 2 cost ( ∆ VO 2 ) for recruited arms was lower in water immersed exercise compared to land based exercise (0.057±0.072 l ·min -1 and 0.367 1±0.057·min -1 , respectively; p=.000). Differences exist in the rate of performing physical work above ventilatory threshold two. Work load values attained on land based exercise surpass that of water immersed exercise (204.2 watts vs. 154.0 watts for whole body work and 227.1 watts vs. 150.0 watts for leg work, respectively). Conclusions: Differences in ∆ VO 2 at a given work rate are to be explained rather from a biome- chanical point of view. More likely ∆ VO 2 in water seems to be influenced by both familiarity of the task and fitness level. Exercise intensity in water need to be selected at lower levels than on land.

Rate Pressure Product During Upper and Lower Body Ergometer Exercise

PURPOSE: Rate Pressure Product (RPP) [the product of heart rate (HR) and systolic blood pressure (SBP)] is strongly correlated with and used as a marker of myocardial oxygen demands (MVO2), with specific utility during exercise in patients with angina pectoris. Subsequently, RPP is monitored during exercise to assure that patients do not exceed their ischemic threshold. Upper and lower body ergometry have different cardiovascular responses, which may alter the RPP response to exercise. Therefore, the purpose of this investigation was to measure HR, SBP and RPP during at similar workrates during upper body and lower body ergometer exercise. METHODS: Fifteen apparently healthy men (age: 22 ± 1.5 yrs) performed incremental (25 Watts every two minutes) arm and leg ergometry on an electronically braked ergometer to volitional fatigue. HR and SBP were measured at the end of each two-minute work stage. RPP was calculated as the product of HR and SBP. A two-way repeated measures ANOVA was used to determine differences between arm and leg ergometry across work stages. RESULTS: HR was significantly greater during arm ergometry when compared to leg ergometry at higher workrates (75 and 100 W) (p<0.001). SBP increased with increasing workrates (p<0.001) but did not differ between arm and leg ergometry. RPP was greater (p=0.003) during arm ergometry at higher workloads when compared to leg ergometry. CONCLUSIONS: HR increased to a greater magnitude during arm ergometry when compared to leg ergometry, particularly during higher workrates. There was a subsequent greater increase in RPP during arm ergometry at higher workrates. Therefore, caution should be practiced when using HR to assure the desired exercise intensity across exercise modalities for patients with ischemic heart disease. Although appropriate for leg ergometry, the prescribed training heart rate may exceed the patient’s ischemic threshold during arm ergometry.

Cardiopulmonary Exercise Testing Demonstrates Maintenance of Exercise Capacity in Patients With Hypoxemia and Pulmonary Arteriovenous Malformations

Patients with pulmonary arteriovenous malformations (PAVMs) are unusual because hypoxemia results from right-to-left shunting and not airway or alveolar disease. Their surprisingly well-preserved exercise capacity is not generally appreciated. To examine why exercise tolerance is preserved, cardiopulmonary exercise tests were performed while breathing room air in 21 patients with radiologically proven PAVMs, including five restudied 3 to 12 months after embolization when their PAVMs had regressed. Where physiologic matching was demonstrable, comparisons were made with 12 healthy control subjects. The majority of patients achieved their predicted work rate despite a resting arterial oxygen saturation (SaO₂) of 80% to 96%. Peak work rate and oxygen consumption (VO₂) were no lower in patients with more hypoxemia. Despite higher SaO₂ following embolization (median, 96% and 90%; P = .009), patients achieved similar work rates and similar peak VO₂. Strikingly, treated patients reset to virtually identical peak oxygen pulses (ie, VO₂ per heart beat) and in many cases to the same point on the peak oxygen pulse/work rate plot. The 21 patients had increased minute ventilation (VE) for given increases in CO₂ production (VE/VCO₂ slope), but perceived dyspnea was no greater than in the 12 control subjects or in the same patients before compared to after embolization comparison. Overall, work rate and peak VO₂ were associated not with oxygenation parameters but with VE/VCO₂ slope, BMI, and anaerobic threshold. Patients with hypoxemia and PAVMs can maintain normal oxygen delivery/VO₂ during peak exercise. Following improvement of SaO₂ by embolization, patients appeared to reset compensatory mechanisms and, as a result, achieved similar peak VO₂ per heart beat and peak work rates.

The role of incline, performance level, and gender on the gross mechanical efficiency of roller ski skating

The ability to efficiently utilize metabolic energy to produce work is a key factor for endurance performance. The present study investigated the effects of incline, performance level, and gender on the gross mechanical efficiency during roller ski skating. Thirty-one male and nineteen female elite cross-country skiers performed a 5-min submaximal session at approximately 75% of VO2peak on a 5% inclined treadmill using the G3 skating technique. Thereafter, a 5-min session on a 12% incline using the G2 skating technique was performed at a similar work rate. Gross efficiency was calculated as the external work rate against rolling friction and gravity divided by the metabolic rate using gas exchange. Performance level was determined by the amount of skating FIS points [the Federation of International Skiing (FIS) approved scoring system for ski racing] where fewer points indicate a higher performance level. Strong significant correlations between work rate and metabolic rate within both inclines and gender were revealed (r = −0.89 to 0.98 and P < 0.05 in all cases). Gross efficiency was higher at the steeper incline, both for men (17.1 ± 0.4 vs. 15.8 ± 0.5%, P < 0.05) and women (16.9 ± 0.5 vs. 15.7 ± 0.4%, P < 0.05), but without any gender differences being apparent. Significant correlations between gross efficiency and performance level were found for both inclines and genders (r = −0.65 to 0.81 and P < 0.05 in all cases). The current study demonstrated that cross-country skiers of both genders used less metabolic energy to perform the same amount of work at steeper inclines, and that the better ranked elite male and female skiers skied more efficiently.

The influence of incline and speed on work rate, gross efficiency and kinematics of roller ski skating

During competitions, elite cross-country skiers produce higher external work rates on uphill than on flat terrain. However, it is not presently known whether this reflects solely higher energy expenditure. Furthermore, the kinematic factors associated with these higher rates of uphill work have not yet been examined. Therefore, in the present investigation the work rate and associated kinematic parameters at similar metabolic rates during roller ski skating on flat and uphill terrains have been compared. Seven elite male skiers performed six 5-min sub-maximal exercise bouts at the same low, moderate and high metabolic rates on 2 and 8% inclines, while roller skiing on a treadmill employing the G3 skating technique. The work rate was calculated as work against gravity and friction, whereas the energetic equivalent of VO(2) was taken as the metabolic rate. Gross efficiency was defined as work rate divided by metabolic rate. Kinematic parameters were analyzed in three dimensions. At the same metabolic rate, the work rate, cycle rate, work per cycle and relative duration of propulsive phases during a cycle of movement were all higher on the 8% than on the 2% incline at all speeds (all P<0.05). At similar work rates, gross efficiency was greater on the 8% incline (P<0.05). In conclusion, these elite skiers consistently demonstrated higher work rates on the 8% incline. To achieve the higher work rates on the steeper incline, these elite skiers employed higher cycle rates and performed more work per cycle, in association with a longer relative propulsive phase.

Eccentric exercise-induced muscle damage dissociates the lactate and gas exchange thresholds

We tested the hypothesis that exercise-induced muscle damage would increase the ventilatory ([Vdot] E) response to incremental/ramp cycle exercise (lower the gas exchange threshold) without altering the blood lactate profile, thereby dissociating the gas exchange and lactate thresholds. Ten physically active men completed maximal incremental cycle tests before (pre) and 48 h after (post) performing eccentric exercise comprising 100 squats. Pulmonary gas exchange was measured breath-by-breath and fingertip blood sampled at 1-min intervals for determination of blood lactate concentration. The gas exchange threshold occurred at a lower work rate (pre: 136 ± 27 W; post: 105 ± 19 W; P < 0.05) and oxygen uptake ([Vdot]O2) (pre: 1.58 ± 0.26 litres · min−1; post: 1.41 ± 0.14 litres · min−1; P < 0.05) after eccentric exercise. However, the lactate threshold occurred at a similar work rate (pre: 161 ± 19 W; post: 158 ± 22 W; P > 0.05) and [Vdot]O2 (pre: 1.90 ± 0.20 litres · min−1; post: 1.88 ± 0.15 litres · min−1; P > 0.05) after eccentric exercise. These findings demonstrate that exercise-induced muscle damage dissociates the [Vdot] E response to incremental/ramp exercise from the blood lactate response, indicating that [Vdot] E may be controlled by additional or altered neurogenic stimuli following eccentric exercise. Thus, due consideration of prior eccentric exercise should be made when using the gas exchange threshold to provide a non-invasive estimation of the lactate threshold.

Short-term effects of bracing on exercise performance in mild idiopathic thoracic scoliosis.

In adolescent idiopathic thoracic scoliosis (ITS) working capacity may be reduced during exercise. Despite concern about its usefulness, bracing is still being used in ITS. Thus the effects of bracing on exercise performance need to be examined. We studied six females, ages 12-15 years who had mild ITS (Cobb angle range 20-35 degrees). Pulmonary volumes, maximal voluntary ventilation (MVV), breathing pattern, the lowest (most negative in sign) pleural pressure during sniff maneuver (Pplsn), and pleural pressure swings (Pplsw) were measured first. Then, Pplsw, O2 uptake (VO2), CO2 output (VCO2), heart rate (HR) at rest and during progressive incremental exercise on a cycling ergometer (10 watts/min) were recorded. The exercise test was performed under control conditions without bracing (C) and after 7 days of bracing with the braced on (B). Dyspnea was measured by a modified Borg scale. At rest, bracing mildly affected total lung capacity and forced vital capacity (p < 0.03 for both) but not breathing pattern, Pplsn, or Pplsw (%Pplsn), a measure of respiratory effort. Furthermore, bracing did not consistently affect maximum work rate (WRmax). In both B and C VO2 was below (< 70%) the predicted value, VE was below (< 45%) MVV, and HR reserve was < 15 beats/min, indicating some cardiovascular deconditioning. On the other hand, respiratory frequency (Rf) increased more in B than in C (p < 0.03). In addition, Pplsw, Pplsw (%Pplsn), and Pplsw (%Pplsn)/VT, an index of neuroventilatory dissociation (NVD) of the respiratory pump, were greater in B (p < 0.03 for all). At a similar work rate, the Borg rating score was greater with bracing on than off, and the difference (delta Borg) tended to relate to concurrent changes in Pplsw (%Pplsn)/VT (r2 = 0.71; p < 0.07). We conclude that bracing affects respiratory effort, NVD, and dyspnea score during progressive exercise. These effects are consistent with increased lung elastance. Diminished exercise tolerance in patients with mild ITS probably reflects impaired physical fitness but is not affected by bracing. Training programs proposed for this subset of patients to increase peripheral muscle performance might also consider NVD of the respiratory pump.

Lactate acidosis and the increase in VE/VO2 during incremental exercise.

The purpose of this investigation was to determine whether the onset of lactate acidosis is responsible for the increase in ventilatory equivalent (VE/VO2) during exercise of increasing intensity. Eight male subjects performed maximal incremental exercise tests on a cycle ergometer on two separate occasions. For the control (C) treatment, the initial work rates consisted of 4 min of unloaded pedaling (60 rpm) and 1 min of pedaling at a work rate of 30 W. Thereafter, the work rate was increased each minute by 22 W until volitional fatigue. Venous blood samples were taken before the onset of exercise and at the end of each work rate for determination of pH and lactate. Ventilatory parameters at each work rate were also monitored. Before the experimental treatment (E), the subjects performed two 3-min work bouts at high intensity (210-330 W) on the cycle ergometer in order to prematurely raise blood lactate levels and lower blood pH. The same incremental exercise test as C was then performed. The results indicated that the increase in VE/VO2 occurred at similar work rates and %VO2max although the venous H+ and lactate concentrations were significantly elevated during the E treatment. These results suggest that a decrease in the blood pH resulting from blood lactate accumulation is not responsible for the increase in VE/VO2 during incremental exercise.

The anaerobic threshold as determined before and during lactic acidosis

During this study the relationships between venous lactate concentration and accociated changes in respiratory gas exchange were investigated. Five men performed two successive incremental exercise tests to exhaustion on an electronically braked cycle ergometer. These tests were separated by a 5 min rest period. During the initial test venous lactate concentrations showed a characteristic curvilinear increase and the anaerobic threshold (AT1) was determined conventionally. During the second test lactate concentrations were still decreasing at higher work rates than the AT1, and a second anaerobic threshold (AT2) was determined as the point where lactate concentrations again increased. The departure from linearity of the ventilatory response to both exercise tests occurred at a similar work rate, irrespective of whether venous lactate concentrations were increasing or decreasing. Carbon dioxide production was similar during the two exercise tests. The anaerobic thresholds as determined by respiratory gas analysis (ATR) were therefore similar for both tests. Results of this study indicate that changing venous lactate concentrations were not responsible for the ventilatory drive which occurred at the ATR. The venous lactate response to work at a constant rate determined within the range AT1-AT2 was also investigated. It was concluded that the lactate response to constant work rate will vary predictably at work rates falling within the AT1 to AT2 range. At AT1 no increase in venous lactate concentrations occurred, while at AT2 these increased progressively, and the test was terminated at varying times (12-15 min) due to subject exhaustion. At work rates determined from the ATR venous lactate concentrations varied according to the placement of the ATR within the AT1 AT2 range.