Heavy-intensity Exercise Research Articles

Oxygen Uptake and Lactate Kinetics in Patients with Chronic Obstructive Pulmonary Disease during Heavy Intensity Exercise: Role of Pedaling Cadence

Oxygen uptake slow component (sc) is associated with lactate accumulation, likely a contribution of poorly oxidative muscle fibers. We aimed to test the hypothesis that higher muscle tension during slow pedaling rates would yield more prominent sc in healthy subjects, but not in COPD patients. Eight severe COPD patients and 8 age-matched healthy individuals performed 4 rest-heavy exercise transitions at 40 and 80 RPM. Work rates at the two cadences were balanced. Venous blood was sampled for measurement of lactate concentration at rest and every 2 minutes until the end of exercise. kinetics were analyzed utilizing nonlinear regression. phase II amplitudes at the two cadences were similar in both groups. In healthy individuals, sc was steeper at 40 than 80 RPM (46.6 ± 12.0 vs. 29.5 ± 11.7 mL/min2, p = 0.002) but not in COPD patients (16.2 ± 14.7 vs. 13.3 ± 7.6 mL/min2). End-exercise lactate concentration did not differ between cadences in either group. In healthy individuals, greater slow-cadence sc seems likely related to oxidative muscle fiber recruitment at higher muscular tension. COPD patients, known to have fast-twitch fiber predominance, might be unable to recruit oxidative fibers at high muscle tension, blunting sc response.

Influence Of “Priming” Exercise On Pulmonary Oxygen Uptake Kinetics During Heavy‐Intensity Cycle Exercise From An Elevated Baseline In Type 2 Diabetes.

In healthy individuals phase II oxygen uptake (V̇ O2) kinetics (τ V̇ O2p) is slower when heavy‐intensity exercise is initiated from a moderate‐intensity exercise baseline (work‐to‐work) than unloaded cycling; but τ V̇ O2p is not enhanced when work‐to‐work exercise is preceded by a prior bout of heavy‐intensity priming exercise (PE). This negates an insufficient muscle O2 availability as the primary culprit in healthy individuals.PurposeGiven that type 2 diabetes (T2D) induces a lengthened τ V̇ O2p during unprimed submaximal exercise compared with healthy controls, which is attributed, at least in part, to limitations in O2 supply, the purpose of the study was to test the hypothesis that heavy‐intensity PE would subsequently accelerate τ V̇ O2p in T2D.MethodsSeven middle‐aged individuals with T2D (46 ± 8 yr) and 7 controls (ND) (41 ± 10 yr) performed four bouts of constant‐load, heavy‐intensity exercise each commencing from a baseline of moderate‐intensity exercise. Two of these work‐to‐work bouts were completed without PE and two bouts were undertaken preceded by PE. V̇O2 kinetics was calculated from continuously measured breath‐by‐breath V̇O2 data, whilst the rate of muscle deoxygenation (i.e., deoxygenated haemoglobin and myoglobin, HHb+Mb) was continuously measured by near‐infrared spectroscopy at the vastus lateralis muscle. Diabetes and priming comparisons were made using two‐way ANOVA with repeated measures.ResultsThe amplitude of the V̇O2 slow component was reduced (P < 0.05) in both groups following PE (T2D: from 0.13 ± 0.15 to 0.08 ± 0.10 l/min; ND: from 0.20 ± 0.18 to 0.12 ± 0.11 l/min). In addition, PE tended to reduce τ V̇ O2p during work‐to‐work cycling transitions in T2D (from 54 ± 14 to 42 ± 17 s) but not in ND (42 ± 11 vs. 41 ± 11 s), bringing the τ V̇ O2p in T2D on a par with their ND counterparts, in the absence of significant changes in the dynamic response of (HHb+Mb). It is likely inter‐individual variability in response precluded the attainment of statistical significance.ConclusionIn middle‐aged individuals with T2D, the enhanced V̇ O2 kinetics response was likely consequent to a priming‐induced increase in muscle blood flow and/or improved muscle perfusion to metabolic rate.Support or Funding InformationThis publication has emanated from research conducted with the financial support of the Health Research Board of Ireland (Grant No HRA_POR/2073/274)This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Oxygen Uptake Kinetics Is Slower in Swimming Than Arm Cranking and Cycling during Heavy Intensity.

Oxygen uptake () kinetics has been reported to be influenced by the activity mode. However, only few studies have compared O2 kinetics between activities in the same subjects in which they were equally trained. Therefore, this study compared the O2 kinetics response to swimming, arm cranking, and cycling within the same group of subjects within the heavy exercise intensity domain. Ten trained male triathletes (age 23.2 ± 4.5 years; height 180.8 ± 8.3 cm; weight 72.3 ± 6.6 kg) completed an incremental test to exhaustion and a 6-min heavy constant-load test in the three exercise modes in random order. Gas exchange was measured by a breath-by-breath analyzer and the on-transient O2 kinetics was modeled using bi-exponential functions. O2peak was higher in cycling (65.6 ± 4.0 ml·kg−1·min−1) than in arm cranking or swimming (48.7 ± 8.0 and 53.0 ± 6.7 ml·kg−1·min−1; P < 0.01), but the O2 kinetics were slower in swimming (τ1 = 31.7 ± 6.2 s) than in arm cranking (19.3 ± 4.2 s; P = 0.001) and cycling (12.4 ± 3.7 s; P = 0.001). The amplitude of the primary component was lower in both arm cranking and swimming (21.9 ± 4.7 and 28.4 ± 5.1 ml·kg−1·min−1) compared with cycling (39.4 ± 4.1 ml·kg−1·min−1; P = 0.001). Although the gain of the primary component was higher in arm cranking compared with cycling (15.3 ± 4.2 and 10.7 ± 1.3 ml·min−1·W−1; P = 0.02), the slow component amplitude, in both absolute and relative terms, did not differ between exercise modes. The slower O2 kinetics during heavy-intensity swimming is exercise-mode dependent. Besides differences in muscle mass and greater type II muscle fibers recruitment, the horizontal position adopted and the involvement of trunk and lower-body stabilizing muscles could be additional mechanisms that explain the differences between exercise modalities.

Respiratory muscle endurance training reduces the O2 cost of cycling and perceived exertion in obese adolescents.

In obesity, the increased O2 cost of breathing negatively affects the O2 cost of exercise and exercise tolerance. The purpose of the study was to determine whether, in obese adolescents, the addition of respiratory muscle endurance training (RMET) (isocapnic hyperpnea) to a standard body mass reduction program decreases the O2 cost of exercise and perceived exertion. Nine male obese adolescents [16.0 ± 1.4 yr (x ± SD), body mass 114.4 ± 22.3 kg] underwent 3 wk of RMET (5 days/week) in addition to a standard body mass reduction program. Eight age- and sex-matched obese adolescents underwent only the standard program (CTRL). Before and after interventions, patients performed on a cycle ergometer: incremental exercise; 12-min exercises at a constant work rate (CWR) of 65% and 120% at the gas exchange threshold (GET) determined before the intervention. Breath-by-breath pulmonary ventilation (V̇e) and O2 uptake (V̇o2), heart rate (HR), and ratings of perceived exertion for dyspnea/respiratory discomfort (RPER) and leg effort (RPEL) were determined. Body mass decreased (by ~3.0 kg) after both RMET (P = 0.003) and CTRL (P = 0.002). Peak V̇o2 was not affected by both interventions. Peak work rate was slightly, but significantly (P = 0.04), greater after RMET but not after CTRL. During CWR < GET, no changes were observed after both interventions. During CWR > GET, the O2 cost of cycling at the end of exercise (P = 0.02), the slope of V̇o2 vs. time (3-12 min) (P = 0.01), RPER (P = 0.01), and RPEL (P = 0.01) decreased following RMET, but not following CTRL. HR decreased after both RMET (P = 0.02) and CTRL (P = 0.03), whereas V̇e did not change. In obese adolescents RMET, superimposed on a standard body mass reduction program, lowered the O2 cost of cycling and perceived exertion during constant heavy-intensity exercise.

Effect of acute nitrate ingestion on V̇O2 response at different exercise intensity domains.

While nitrate supplementation influences oxygen uptake (V̇O2) response to exercise, this effect may be intensity dependent. The purpose of this study was to investigate the effect of acute nitrate supplementation on V̇O2 response during different exercise intensity domains in humans. Eleven men ingested 10 mg·kg-1 body mass (8.76 ± 1.35 mmol) of sodium nitrate or sodium chloride (placebo) 2.5 h before cycling at moderate (90% of gas exchange threshold; GET), heavy (GET + 40% of the difference between GET and peak oxygen uptake (V̇O2peak), Δ 40) or severe (GET + 80% of the difference between GET and V̇O2peak, Δ 80) exercise intensities. Volunteers performed exercise for 10 min (moderate), 15 min (heavy) or until exhaustion (severe). Acute nitrate supplementation had no effect on any V̇O2 response parameters during moderate and severe exercise intensities. However, the V̇O2 slow amplitude (nitrate: 0.93 ± 0.36 L·min-1 vs. placebo: 1.13 ± 0.59 L·min-1, p = 0.04) and V̇O2 slow gain (nitrate: 5.81 ± 2.37 mL·min-1·W-1 vs. placebo: 7.09 ± 3.67 mL·min-1·W-1, p = 0.04) were significantly lower in nitrate than in placebo during the heavy exercise intensity. There was no effect of nitrate on plasma lactate during any exercise intensity (p > 0.05). Time to exhaustion during the severe exercise intensity was also not affected by nitrate (p > 0.05). In conclusion, acute nitrate supplementation reduced the slow component of V̇O2 only when performing heavy-intensity exercise, which might indicate an intensity-dependent effect of nitrate on V̇O2 response.

Far-infrared Emitting Fabric Improves Aerobic Metabolism, Oxidative Stress and Exercise Tolerance, Independent of Nitric Oxide

Studies have shown that FIR emitted by materials can, without change temperature, enhance cell metabolism and function, increase cellular availability of nitric oxide (NO) and Ca2+, improve blood circulation and an ex-vivo study of skeletal muscle has shown the effect of delay fatigue. However, the effectiveness of FIR fabric as ergogenic aid and its related mechanism in humans remains unknown. PROPOSE: Analyze the effect of fabric made by polyamide fiber mixed to FIR emitting substances on exercise bioenergetics, oxidative stress, NO and exercise tolerance. METHODS: Eighteen active men performed two ergoespirometric tests, two familiarizations and two testing days composed by a square-wave cycling exercise at moderate intensity (2 sets of 10 min), followed by very heavy intensity until exhaustion. Tests occurred two weeks apart and after 96 hours of FIR or Placebo fabric usage, in a crossover, double-blind, placebo-controlled design. The exercise oxygen uptake, lactate accumulation and fast VO2 off-kinetics were used to calculate Aerobic (Ae), Anaerobic Lactic (AnL) and Anaerobic Alactic (AnA) metabolism relative to total energy expenditure values, using the GEDAE-LaB software. Thigh temperature was measured by an infrared thermometer, oxidative stress by gas chromatography–tandem mass spectrometry measurements of F2-isoprostanes, NO by chemiluminescence analysis of Nitrite and Nitrate. RESULTS: There were no differences for any variable between FIR and Placebo fabrics pre-tests and post-moderate exercise. For the very heavy exercise until exhaustion, exercise time was higher for FIR than Placebo (403±127s vs. 338±110s, p=0.004). Relative energy system contributions (%) were as followed: Ae (FIR 66.48±10.91 - Placebo 61.44±15.58, p=0.04); AnL (FIR 21.41±5.63 - Placebo 23.02±6.53, p>0.05); AnA (FIR 12.10±9.38 - Placebo 15.53±13.69, p>0.05). Temperature (°C) were not different between fabrics (FIR 31.8±1.6 - Placebo 31.9±2.2, p>0.05). F2-isoprostanes (pg/dl) just increase for Placebo (pre 216.75±52.78 – post-VH 291.53±88.95, p=0.005). CONCLUSION: Far-infrared emitting fabric enhances aerobic metabolism, reduced oxidative stress and improves exercise tolerance during very heavy intensity exercise, independent of NO availability.

Recreationally-Trained Subjects are Unable to Attenuate VO2 Slow Component During Severe Exercise Using RPE

Previous research indicates that recreationally-trained subjects are able to attenuate the slow component of oxygen uptake (VO2) during heavy intensity exercise using rating of perceived exertion (RPE). Little is known, however, about the use of RPE to attenuate the slow component when exercising in the severe exercise domain. PURPOSE: The present study examined the degree to which recreationally-trained subjects could attenuate the VO2 slow component while cycling in the severe exercise domain. METHODS: A total of 15 volunteer subjects, 9 males, and 6 females (mean age ± SD = 22.3 ± 1.8), completed a 3-minute all-out exercise test for the determination of critical power (CP) and the curvature constant (W’). Subjects then returned and completed two separate bouts at 10% > CP. The constant bout required subjects to sustain their preferred cadence until exhaustion. The regulated bout involved subjects attempting to maintain their RPE from 2-min into the bout by adjusting power output until their power output declined to a value ≤ CP. STATISICAL ANALYSIS: Paired t-tests were conducted. RESULTS: The constant bout evoked a VO2 value (43.3 ± 7.3 ml·kg-1·min-1) that was not different from VO2max (43.1 ± 7.4 ml·kg-1·min-1) (t = 0.17, p = 0.87), confirming that the intensity was in the severe exercise domain. In the regulation bout, there was a significant gain (∼7 ml·kg-1·min-1) in VO2 between 2 min and the end of exercise (t = 6.25, p < 0.01). A wide range of utilization for the work capacity above CP was observed (2.0 - 13.7 kJ). CONCLUSION: In contrast to exercise in the heavy domain, recreationally-trained subjects are unable to attenuate the VO2 slow component using their RPE in the severe domain. Future research is needed on fitter subjects and/or different psychometric scales.

The Effects of Maximally Achievable Cycling Cadence on Carbohydrate Management at Moderate and Heavy Exercise Intensity.

Effects of different cycling cadences (revolutions/min [rpm]) on metabolic rate, blood lactate concentration (BLC), and reliance on carbohydrate (CHO) defined as the fraction of oxygen uptake used for CHO oxidation (relCHO) are highly individual. Whether this depends on the individually maximal achievable rpm obtained at minimized cycling resistance (rpmmax) is unknown. The authors tested the hypotheses that the individual freely chosen rpm in an incremental cycle-ergometer test (ILT) and relCHO at given BLC levels both depend on rpmmax. Seven master cyclists and 8 not specifically trained leisure athletes performed an ILT at individually freely chosen rpm and an rpmmax test. Respiratory data and BLC were measured; relCHO was plotted as a function of the BLC for the determinations of the individual BLC at relCHO of 75% and 95% (BLC75% and BLC95%). With 16.7%, the between-subjects variability of individual rpm was high but independent from rpmmax. In the master athletes,rpmmax explained 59.3% and 95.2% of BLC75% (P = .043) and BLC95% (P = .001), respectively. Irrespective of cycling experience, the individually preferred average rpm at submaximal stages of an ILT is highly variable and independent of rpmmax. In experienced cyclists, carbohydrate management defined as the ratio between substrate availability as indicated by BLC and relCHO depends on rpmmax.

Attenuation of the Oxygen Uptake Slow Component During Intermittent Compared to Continuous Heavy Intensity Exercise

Attenuation of the Oxygen Uptake Slow Component During Intermittent Compared to Continuous Heavy Intensity Exercise

The effect of different intensity exercise on skeletal muscle fiber MHC subtype transformation and CaN/NFATc1 signaling pathways

To study the effect of different intensity exercise on skeletal muscle fiber myosin heavy chain(MHC) subtype transformation and CaN/NFATc1 signaling pathways. Twenty-four Male SD rats (2-month old) were randomly divided into normal control group (NC), moderate intensity exercise group (ME, grade 5°, speed 18 m/min), heavy intensity exercise group (HE, grade 10°, 26.8 m/min). The rats in exercise groups were treated with treadmill training for eight weeks. The type I and type Ⅱ muscle fibers were determined by ATPase staining method. MHC subtype was separated by SDS-PAGE. The activity of CaN was determined by colorimetric method. The content of NFATc1 protein in skeletal muscle was detected by immune imprinting technology. ①Skeletal muscle fiber density changes:the type I and Ⅱ fiber number density of quadriceps in ME group were increased significantly (P<0.05), but in HE group, only the type Ⅱ fiber surface density was increased significantly (P<0.05). The type I fiber number density of soleus in ME and HE group was increased significantly (P<0.05). ②The changes of fibers MHC subtype percentage in skeletal muscle:the percentages of MHC I and type Ⅱa of quadriceps in ME group were increased (P<0.05), while the percentage of MHC Ⅱb was decrease (P<0.05). The percentage of MHC I in soleus was increased, while the percentages of MHCⅡa and Ⅱb were decreased. ③The activity of CaN and the content of NFATc1 protein in ME group were increased significantly (P<0.05). The heavy and moderate intensity exercise may induce skeletal muscle MHC type transforming from fast to slow. At the same time, the activity of CaN and the expression of NFATc1 protein are increased accompanying the changes of skeletal muscle fibers subtype.

Imposed expiratory resistance, hyperinflation, and dyspnea are dissociated from locomotor fatigue during moderate exercise

Expiratory flow resistance (e.g. asthma, chronic obstructive pulmonary disease) results in dyspnea, dynamic hyperinflation, and premature exercise intolerance during heavy intensity exercise. This cascade seems to be primarily precipitated by abnormal lung mechanics that result in exacerbated symptoms and reduced maximal evocable limb motor activity. We do not know whether this cascade behaves in the same way during moderate exercise where only modest locomotor fatigue is expected to develop.We hypothesized that expiratory flow resistance would result in dynamic hyperinflation, dyspnea, and exacerbated locomotor fatigue during moderate intensity exercise in a similar manner to that during heavy intensity exercise.Volunteers (N=10, 27±6 yr) completed constant power moderate exercise (50% peak ramp power) with 3 levels of imposed expiratory flow resistance (7, 9, 11 cm H2O·L·s−1) or control (no imposed flow resistance). We measured operating lung volumes during exercise with inspiratory capacity maneuvers. Participants reported dyspnea and leg effort using a Borg 10‐point scale. At the termination of exercise we used a rapid switch from hyperbolic to isokinetic cycling to measure the decline in peak isokinetic power (Piso).Decline in Piso was not different when expiratory flow resistance was imposed (p&gt;0.05). Inspiratory capacity was smaller at the end of exercise in the most severe resistance (11 cm H2O·L·s−1) as compared to control (2.31±1.52 vs. 3.15±0.71 L; p&lt;0.05). Similarly, inspiratory reserve volume was smaller at the end of exercise in the most severe resistance as compared to control (−0.07±1.28 vs. 0.82±0.43 L; p&lt;0.05). Dyspnea was greater at the end of exercise in both mild and severe resistance (7 and 11 cm H2O·L·s−1) as compared to control (5.7±2.5 and 5.2±1.9 vs. 3.7±1.6; p&lt;0.05). Piso was not related to inspiratory reserve volume, inspiratory capacity, or dyspnea (p&gt;0.05).Imposed severe expiratory flow resistance results in hyperinflation and exacerbated dyspnea in healthy volunteers. Unlike what we have found during heavy exercise, however, abnormal lung mechanics and dyspnea were not related to maximal locomotor power during moderate exercise.

Pulmonary oxygen uptake and muscle deoxygenation kinetics during heavy intensity cycling exercise in patients with emphysema and idiopathic pulmonary fibrosis

BackgroundLittle is known about the mechanistic basis for the exercise intolerance characteristic of patients with respiratory disease; a lack of clearly defined, distinct patient groups limits interpretation of many studies. The purpose of this pilot study was to investigate the pulmonary oxygen uptake ( overset{.}{V} O2) response, and its potential determinants, in patients with emphysema and idiopathic pulmonary fibrosis (IPF).MethodsFollowing a ramp incremental test for the determination of peak overset{.}{V} O2 and the gas exchange threshold, six emphysema (66 ± 7 years; FEV1, 36 ± 16%), five IPF (65 ± 12 years; FEV1, 82 ± 11%) and ten healthy control participants (63 ± 6 years) completed three repeat, heavy-intensity exercise transitions on a cycle ergometer. Throughout each transition, pulmonary gas exchange, heart rate and muscle deoxygenation ([HHb], patients only) were assessed continuously and subsequently modelled using a mono-exponential with ( overset{.}{V} O2, [HHb]) or without (HR) a time delay.ResultsThe overset{.}{V} O2 phase II time-constant (τ) did not differ between IPF and emphysema, with both groups significantly slower than healthy controls (Emphysema, 65 ± 11; IPF, 69 ± 7; Control, 31 ± 7 s; P < 0.05). The HR τ was slower in emphysema relative to IPF, with both groups significantly slower than controls (Emphysema, 87 ± 19; IPF, 119 ± 20; Control, 58 ± 11 s; P < 0.05). In contrast, neither the [HHb] τ nor [HHb]:O2 ratio differed between patient groups.ConclusionsThe slower overset{.}{V} O2 kinetics in emphysema and IPF may reflect poorer matching of O2 delivery-to-utilisation. Our findings extend our understanding of the exercise dysfunction in patients with respiratory disease and may help to inform the development of appropriately targeted rehabilitation strategies.

Tracking changes in the upper boundary of the heavy-intensity exercise domain:

&lt;div&gt;The aim of this study was to compare how respiratory compensation point (RCP) and end-test power (EP) change in response to the same four-week high intensity interval training (HIIT). The power output associated with RCP and EP before and after HIIT were recorded in 24 recreationally-active participants (14 men and 10 women). RCP was determined from an incremental exercise test and EP was derived from a three-minute maximal effort test on a cycle ergometer. A significant time (pretest/posttest) × measurement (EP/RCP) interaction was found (F(1, 23)=5.119, p&amp;lt;.05). Results from a paired-sample t-test indicated that both EP (t(23)= -5.221, p&amp;lt;.05) and RCP (t(23)=-3.049, p&amp;lt;.05) increased significantly from pretest to posttest. Furthermore, a small effect size (d=.36, 90%CI=[.13, .58]) was calculated for the pre/posttest changes in the examined thresholds indicating greater potential improvements in EP compared to RCP. The pre/posttest change in EP (mean=21 W, 90%CI=[14, 28 W]) exceeded its standard error of estimate (14 W), while RCP did not. Correlation analysis revealed that EP correlated with RCP at both pretest (r=.813, p&amp;lt;.05) and posttest (r=.873, p&amp;lt;.05), however, delta values between the two measures were not significantly related. Both EP and RCP can be used to assess the change of aerobic capacity after HIIT, but may be reflective of different physiological adaptations. Further, EP may be preferred over RCP when assessing the effects of HIIT.&lt;/div&gt;

Effect of heavy-intensity ‘priming’ exercise on oxygen uptake and muscle deoxygenation kinetics during moderate-intensity step-transitions initiated from an elevated work rate

We examined the effect of heavy-intensity ‘priming’ exercise on the rate of adjustment of pulmonary O2 uptake (τV˙O2p) initiated from elevated intensities. Fourteen men (separated into two groups: τV˙O2p≤25s [Fast] or τV˙O2p>25s [Slow]) completed step-transitions from 20W to 45% lactate threshold (LT; lower-step, LS) and 45% to 90%LT (upper-step, US) performed (i) without; and (ii) with US preceded by heavy-intensity exercise (HUS). Breath-by-breath V˙O2p and near-infrared spectroscopy-derived muscle deoxygenation ([HHb+Mb]) were measured. Compared to LS, τV˙O2p was greater (p<0.05) in US in both Fast (LS, 19±4s; US, 30±4s) and Slow (LS, 25±5s; US, 40±11s) with τV˙O2p in US being lower (p<0.05) in Fast. In HUS, τV˙O2p in Slow was reduced (28±8s, p<0.05) and was not different (p>0.05) from LS or Fast group US. In Slow, τ[HHb+Mb] increased (p<0.05) in US relative to HUS; this finding coupled with a reduced τV˙O2p indicates a priming-induced improvement in matching of muscle O2 delivery-to-O2 utilization during transitions from elevated intensities in those with Slow but not Fast V˙O2p kinetics.

Gender differences in V˙O2 and HR kinetics at the onset of moderate and heavy exercise intensity in adolescents.

The majority of the studies on V˙O2 kinetics in pediatric populations investigated gender differences in prepubertal children during submaximal intensity exercise, but studies are lacking in adolescents. The purpose of this study was to test the hypothesis that gender differences exist in the V˙O2 and heart rate (HR) kinetic responses to moderate (M) and heavy (H) intensity exercise in adolescents. Twenty‐one healthy African‐American adolescents (9 males, 15.8 ± 1.1 year; 12 females, 15.7 ± 1 year) performed constant work load exercise on a cycle ergometer at M and H. The V˙O2 kinetics of the male group was previously analyzed (Lai et al., Appl. Physiol. Nutr. Metab. 33:107–117, 2008b). For both genders, V˙O2 and HR kinetics were described with a single exponential at M and a double exponential at H. The fundamental time constant (τ 1) of V˙O2 was significantly higher in female than male at M (45 ± 7 vs. 36 ± 11 sec, P < 0.01) and H (41 ± 8 vs. 29 ± 9 sec, P < 0.01), respectively. The functional gain (G1) was not statistically different between gender at M and statistically higher in females than males at H: 9.7 ± 1.2 versus 10.9 ± 1.3 mL min−1 W−1, respectively. The amplitude of the slow component was not significantly different between genders. The HR kinetics were significantly (τ 1, P < 0.01) slower in females than males at M (61 ± 16 sec vs. 45 ± 20 sec, P < 0.01) and H (42 ± 10 sec vs. 30 ± 8 sec, P = 0.03). The G1 of HR was higher in females than males at M: 0.53 ± 0.11 versus 0.98 ± 0.2 bpm W−1 and H: 0.40 ± 0.11 versus 0.73 ± 0.23 bpm W−1, respectively. Gender differences in the V˙O2 and HR kinetics suggest that oxygen delivery and utilization kinetics of female adolescents differ from those in male adolescents.

Heart Rate and Energy Expenditure in Division I Field Hockey Players During Competitive Play.

Sell, KM and Ledesma, AB. Heart rate and energy expenditure in Division I field hockey players during competitive play. J Strength Cond Res 30(8): 2122-2128, 2016-The purpose of this study was to quantify energy expenditure and heart rate data for Division I female field hockey players during competitive play. Ten female Division I collegiate field hockey athletes (19.8 ± 1.6 years; 166.4 ± 6.1 cm; 58.2 ± 5.3 kg) completed the Yo-Yo intermittent endurance test to determine maximal heart rate. One week later, all subjects wore a heart rate monitor during a series of 3 matches in an off-season competition. Average heart rate (AvHR), average percentage of maximal heart rate (AvHR%), peak exercise heart rate (PExHR), and percentage of maximal heart rate (PExHR%), time spent in each of the predetermined heart rate zones, and caloric expenditure per minute of exercise (kcalM) were determined for all players. Differences between positions (backs, midfielders, and forwards) were assessed. No significant differences in AvHR, AvHR%, PExHR, PExHR%, and %TM were observed between playing positions. The AvHR% and PExHR% for each position fell into zones 4 (77-93% HRmax) and 5 (>93% HRmax), respectively, and significantly more time was spent in zone 4 compared with zones 1, 2, 3, and 5 across all players (p ≤ 0.05). The kcalM reflected very heavy intensity exercise. The results of this study will contribute toward understanding the sport-specific physiological demands of women's field hockey and has specific implications for the duration and schedule of training regimens.

Reply from Glenn M. Stewart, Justin J. Kavanagh, Luke J. Haseler and Surendran Sabapathy

We thank the authors of the Letter to the Editor for their interest in our recent publication in The Journal of Physiology, where we examined cardiac responses – ventricular strain and cardiac troponin – to two acute bouts of prolonged constant-load exercise of different intensities and duration but matched for total work. The exercise intensities we selected straddled the gas exchange threshold (GET), which we used as a non-invasive estimate of the onset of blood lactate accumulation, or lactate threshold. The GET is an important exercise intensity descriptor as it demarcates the boundary between the moderate and heavy exercise intensity domains (Whipp, 1996). Our primary conclusions from this study were that the magnitude and time course of exercise-induced cardiac perturbations are intensity dependent. Nicolo et al. (2016b) question our methodological approach of matching the exercise bouts for total work completed and, consequently, our conclusions drawn from the results of the study. The authors propose matching exercise bouts based on perceived effort (‘isoeffort’), rather than total work, as a superior approach that will provide clearer outcomes.

The First Muscle Oxyhemoglobin Inflection Point Is Correlated To Gas Exchange Threshold And Time-To-Exhaustion During Heavy Intensity Exercise

PURPOSE: The twofold aim of the study was to: 1) compare the gas exchange threshold (GET), the first oxyhemoglobin inflection point ([O2Hb]-T), and perceptual threshold as determined during an incremental exercise test, and 2) investigate the link between each threshold and time-to-exhaustion during heavy intensity exercise. METHODS: Fourteen competitive cyclists performed an incremental exercise test to exhaustion on a cycloergometer to determine the different thresholds and peak workload (Wpeak). The participants then performed a sub-maximal constant workload test (90% Wpeak) to exhaustion to determine time-to-exhaustion. The thresholds were identified from: 1) the first breakpoint in the oxygen uptake vs carbon dioxide output curve (GET), 2) the first muscle oxyhemoglobin inflection point ([O2Hb]-T), and 3) a rating of 13 in perceived exertion (perceptual threshold: RPE13-T). RESULTS: Oxygen uptake at the different thresholds was not significantly different (P > 0.05). Moreover, GET and [O2Hb]-T were significantly correlated: (1) to each other (r ≥ 0.79; P ≤ 0.001) and (2) to time-to-exhaustion (r = 0.81 and r = 0.72, respectively; P < 0.01). RPE13-T, however, was not significantly correlated with the time-to-exhaustion (P = 0.148). CONCLUSIONS: The ‘anaerobic threshold’ as identified from GET was concomitant to [O2Hb]-T. Both thresholds were correlated to time-to-exhaustion, and could therefore be used as a performance index in middle-duration events.

Effect of Blood Flow Restricted Cycle Training on Oxygen uptake kinetics during Exercise

A number of studies have illustrated that blood flow restricted (BFR) resistance training increasing muscle function even when low-intensity training is utilized. Recently BFR has also applied to aerobic training; however less is known about the effect of aerobic training with BFR on the oxygen uptake (VO2) kinetic responses during exercise with or without BFR. PURPOSE: To elucidate the effects of 8-weeks cycle training with BFR on VO2 kinetics at the onset of constant-load cycle exercise with or without BFR. METHODS: Eighteen healthy subjects were randomly assigned to BFR (n = 9; 22±5 yrs) or no BFR group serving as the control (CON; n = 9; 21±2 yrs). Both groups trained for 30 minutes, 3 days/week for 8 weeks. BFR was performed for 5 minutes every 10 minutes by applying cuffs to the upper thighs. Breath-by-breath VO2 was measured during the performance of 5-min moderate intensity (below the lactate threshold) or 6-min heavy intensity exercise (above the lactate threshold) without BFR at Pre-, 4 weeks after (Mid-), and Post-training. At Post, we also measured VO2 kinetics during exercise with BFR (Post+BFR). Two-way repeated ANOVAs were used (BFR vs CON and Pre vs Mid vs Post vs Post+BFR) with significance accepted as p<0.05; and Tukey’s post hoc tests utilized as needed. RESULTS: Although time constant (τ) of VO2 kinetics at the fast component during moderate exercise fitted the exponential model was significantly faster in Mid and Post than that of Pre (26.8 to 16.3 and 15.5 s and 27.5 to 22.1 and 18.5 s in BFR and CON, p<0.05, respectively), significant group-by-time interaction was not detected. The amplitude of the VO2 slow component during heavy exercise significantly decreased in Mid and Post than that of Pre (281 to 103 and 128 mL/min and 300 to 154 and 160 mL/min in BFR and CON, p<0.05, respectively), while a significant group-by-time interaction was not detected. Both τ of VO2 kinetics during moderate exercise and the amplitude of the VO2 slow component during heavy exercise significantly increased from Post to Post+BFR (19.1 and 28.0 s, and 266 and 256 mL/min in BFR and CON, p<0.05, respectively); however significant group-by-time interactions were not detected either. CONCLUSION: Appling the BFR to eight-weeks cycle training showed no further change in VO2 kinetics at the onset of exercise. Supported by KAKENHI (23700788)

Moderate Versus Heavy Intensity Interval Training For Vascular Health In Post-menopausal Women

PURPOSE: Whilst the menopause has been associated with a decline in vascular function, sedentary postmenopausal women report a dislike of heavy intensity exercise. This study aimed to compare the impact of moderate (MOD) versus heavy (HVY) intensity interval exercise training upon vascular function and endothelial integrity. METHODS: 27 sedentary post-menopausal women completed either MOD (90% lactate threshold (LT) 10:10 s duty cycle) or HVY (120% LT 30:30 s duty cycle) interval exercise training twice per week for 12 weeks. Endothelial function (FMD), peak oxygen uptake (VO2peak), LT, circulating angiogenic cell number (FACS) and adhesive capacity to cultured saphenous vein vascular smooth muscle cells (VSMCs) were recorded prior to and following training. Group and time differences were assessed via two-way mixed mode ANOVA. RESULTS: VO2peak and LT increased in HVY only (VO2peak: MOD: 29.97 ±5.5 to 29.65 ± 5.4; HVY: 30.18 ±5.3 to 32.25 ±6.5 ml/kg/min; interaction P=0.02; LT: MOD: 1.13 ±0.19 to 1.11 ±0.18; HVY 1.09 ±0.15 to 1.22 ±0.17 L/min; interaction P=0.005). FMD (group mean: 4.7 ±2.4 %), brachial diameter (group mean: 3.7 ±0.3 mm) and blood pressure were unaffected by training (P>0.05), whilst peripheral arterial stiffness decreased post training in both groups (-0.58 a.u). [CD34+CD45dim] increased after MOD but not after HVY intensity interval training (MOD: 5.3 ±3.8 to 8.9 ±6.3; HVY: 6.34 ±3.1 to 5.7 ±2.6 CAC/105 leucocytes: interaction P=0.02). The adhesive capacity of CACs to VSMCs was seen to increase by 70% following MOD but only 12 % following HVY (P>0.05), this capacity persisted over 60 min in the MOD group (time x group interaction: P=0.05). CONCLUSION: In post-menopausal women HVY intensity interval training provided greater benefits for cardiorespiratory fitness. However, MOD intensity intervals produced equivalent reductions in arterial stiffness and greater modulation of CAC function perceived as beneficial to endothelial integrity. Neither intensity was sufficient to produce significant changes in FMD. Varying the intensities used in interval exercise prescription may provide the most effective cardiovascular benefits in post-menopausal women.