PURPOSE: Prior research shows conflicting findings related to changes, or lack thereof, in exercise performance throughout the menstrual cycle in female athletes. The aim of this case study was to determine if menstrual cycle phase influences cardiorespiratory response and energy expenditure during near-maximal exercise in female endurance athletes. METHODS: A female endurance runner and endurance cyclist were recruited. Neither participant used hormonal birth control, and both exercised aerobically for over 300 minutes per week. Each athlete underwent testing in an exercise physiology laboratory during the follicular and luteal phases of their menstrual cycle to determine VO2max, resting and activity energy expenditure, relative perceived exertion (RPE), heart rate (HR), and respiratory exchange ratio (RER) during 30 minutes of exercise on a treadmill or stationary bike. Each athlete’s data was compared on an intraindividual basis. Significance was set at p = 0.05. RESULTS: RPE significantly differed between the follicular and luteal phase for the runner (p = .01). RER differed significantly between the follicular and luteal phase for the cyclist (p < .001) only. Both athletes experienced significantly higher heart rates during the luteal phase compared to the follicular phase (p < .001). Both athletes had a lower REE during the luteal phase relative to the follicular phase, but the difference was not significant. CONCLUSION: This case study demonstrates that menstrual cycle phase may influence cardiorespiratory response and energy expenditure during near-maximal exercise in female endurance athletes. Further research investigating this relationship is recommended and has the potential to influence fueling, training, recovery plans and ultimately the overall health and performance of female endurance athletes.

Estimating energy expenditure (EE) during exercise is important for tracking energy balance as well as maintaining EE as an individual becomes more accustom to exercise. Technological advances have led to the purported ability of heart rate (HR) monitors to accurately estimate EE based on user indicated activity (e.g., resistance training, interval training, etc.). However, the accuracy of these devices using “multi-sport” has yet to be established. PURPOSE. To determine the accuracy of user indicated activity HR chest strap monitors for estimating EE. METHODS. Fourteen males (n=14) ages 20-36 yrs completed two circuit weight training protocols with integrated high-intensity interval training. Both trials were equated for total volume-load and lasted exactly 43.25 min. Following the exercise portion, each participant completed a 20-min excess post-exercise oxygen consumption measurement. Prior to each exercise protocol the HR monitor watch was set using individual subject anthropometric data and age. Heart rate was continuously monitored during the trials by watch device and portable metabolic analyzer. Comparisons of EE (kcal) were performed between estimations by HR monitor and via indirect calorimetry. Device comparisons for EE were made using paired t-tests, Pearson correlation and Bland-Altman analysis (SPSS v22; p ≤.05). RESULTS. Estimated EE was significantly higher with the user indicated activity HR monitor chest strap compared to indirect calorimetry (596.9 ±121.2 kcal vs. 484.2 ±44.9 kcal, p<.001). Correlational analysis determined there was a significant moderate-strong positive relationship between HR monitor and indirect calorimetry (r=0.56, p=.002) Average HR during the protocol was 149.7 ±14.3 bpm and percent-maximum HR was 78.5 ±5.9%. CONCLUSION. Despite accounting for activity type in the EE estimation software, HR derived estimations of EE appear to be far higher than those estimated by indirect calorimetry during high-intensity activity. Specifically, this is true for vigorous intensity exercise as indicated by %HRmax.

Skeletal muscle contractions are associated with physical stimuli that act upon muscle vasculature, including increased shear stress and blood pressure. It is unclear if acute dynamic exercise alters local vascular function. The purpose of this study was to examine the role of exercise hemodynamics on the effects of acute exercise on vascular function, as evaluated by brachial artery flow-mediated dilation (FMD). Healthy individuals (n = 14; age, 18-34 years) performed 30 min of handgrip exercise at fast and slow contractions. Blood pressure during exercise was measured using a Vasotrac system (Medwave Inc.), while shear rate during exercise and FMD at rest and after 30 min of recovery from exercise were measured in the brachial artery of the active arm using Doppler ultrasound. Estimated contractile work was correlated with blood pressure (r = 0.61, p < 0.01) and retrograde shear rate (r = -0.78, p < 0.01). As a result, blood pressure was higher (p < 0.05) and oscillatory shear index was lower (p < 0.05) during slow as compared with fast contractions. On average, FMD was unchanged following fast contractions (5.4 ± 3.4%dilation to 6.1 ± 3.8%dilation; p = 0.19), but significantly reduced following slow contractions (6.9 ± 4.2%dilation to 3.6 ± 2.5%dilation; p = 0.01). Within slow contractions, subgroup analysis revealed blood pressure to associate with the change in FMD; such that individuals with mean blood pressure >100 mm Hg (range, 102-139 mm Hg) during exercise had larger decreases in FMD than individuals with lower exercise blood pressure. These results indicate that impaired local vascular function following acute exercise with high contractile activity is associated with blood pressure stimuli in healthy individuals.

Skeletal muscle contractions induce physical and chemical stress upon the peripheral vasculature; however, little is known about the acute effects of exercise on endothelial function. PURPOSE: The purpose of this study was to test the hypothesis that endothelial-dependent dilation, as evaluated by brachial artery flow-mediated dilation (FMD), would be unaltered following acute exercise. METHODS: Young men and women (N=15, 18-34 y) performed 30 min of dynamic handgrip exercise at fast and slow contraction rates in order to vary contractile work. The hemodynamic response to exercise and FMD was measured using Doppler ultrasound. FMD was measured at rest and after 30 min of recovery from exercise. Plasma markers of oxidative stress (protein carbonyls and TBARS) were measured using standard assays. RESULTS: External workload was identical between contraction rates (3.4 ± 0.9 kg), but estimated contractile work was higher during exercise with slow versus fast contractions (P<0.05). Shear stress during exercise was similar between contraction rates. Exercise with fast contractions did not change plasma oxidative stress and had no effect on FMD (5.4 ± 3.4 to 6.1 ± 3.8 %dilation; P=0.19). In contrast, exercise with slow contractions increased protein carbonyls by 78% (P<0.05), decreased TBARS by 22% (P<0.05), and decreased FMD (6.9 ± 4.2 to 3.6 ± 2.5 %dilation; P<0.05). The change in FMD was associated with contractile work (r = -0.50, P < 0.05) but not with shear stress or plasma oxidative stress. CONCLUSIONS: We conclude that acute dynamic handgrip exercise with high contractile activity can attenuate endothelial function in healthy humans.

UNLABELLED Participation in regular aerobic exercise has been shown to increase arterial size and that exercise-induced vascular remodeling may be regional rather than systemic. However, these issues have been minimally investigated concerning resistance training. PURPOSES To determine whether 1) resistance training of the nondominant arm elicits an increase in diameter of the brachial artery and 2) unilateral training induces arterial remodeling in the contralateral arm. METHODS Twenty-four previously untrained participants, consisting of 18 females (aged 22.3 +/- 5.1 yr) and 6 males (aged 21.7 +/- 1.8 yr), participated in unilateral strength training of the biceps and triceps for 12 wk using their nondominant arm. Isotonic (one-repetition maximum, 1RM) and isometric (ISO) strength of the biceps were assessed before and after training on both arms. Brachial artery diameter and biceps muscle cross-sectional area (CSA) of both arms were also measured before and after training using magnetic resonance imaging (MRI). RESULTS Brachial artery diameter increased 5.47% (P < 0.05) in the nondominant trained arm with no change observed in the dominant untrained arm. Biceps CSA increased 18.3% (P < 0.05) in the trained arm with no change (P > 0.05) in the untrained limb. Nondominant 1RM and ISO strength increased by 35.1% and 16.8%, respectively (P < 0.05 for both), although there were no significant changes (P > 0.05) in the contralateral arm. A modest correlation was found between the increases in CSA and in brachial artery diameter (r2 = 0.19, P = 0.039). CONCLUSIONS These results indicate that upper arm vascular remodeling, manifesting as increased brachial artery diameter, can result from resistance training and that these changes are localized to the trained limb and associated with increases in CSA.

Shear stress is the frictional force of blood against the endothelium, a stimulus for endothelial activation and the release of von Willebrand factor (vWF). This study tested the hypothesis that the increase in shear stress associated with exercise correlates with plasma vWF. Young (n = 14, 25.7 ± 5.4 years) and older (n = 13, 65.6 ± 10.7 years) individuals participated in 30 min of dynamic handgrip exercise at a moderate intensity. Brachial artery diameter and blood flow were measured using ultrasound Doppler and blood samples were collected before, immediately after, and following 30 min of recovery from exercise with plasma levels of vWF. Plasma levels of vWF increased (P < 0.05) by 6 ± 2% in young individuals and 4 ± 1% in older individuals immediately after exercise. The change in plasma vWF was linearly correlated with the increase in shear stress during exercise in older individuals (post-exercise: r = 0.78, 30 min recovery: r = 0.77, P < 0.01), but no association was found in the young individuals. These changes in plasma levels of vWF in humans suggest that aging influences endothelial activation and hemostasis.

To test the hypothesis that retrograde flow influences the shear stimulus of exercise blood flow, eight healthy men [25.6+/-3.1 years (SD)] performed 20 min of single-leg knee-extension exercise at two contraction velocities: fast (FR, 1.5 m s(-1)) and slow (SR, 0.4 m s(-1)). Contraction frequency (30 cpm) and workload (5 kg) were kept constant resulting in a work rate of 15.25 W for both contraction velocities. Common femoral artery diameter and blood velocity were measured at rest and during exercise using ultrasound Doppler. Mean blood flow was not different between contraction velocities while antegrade (2012.4+/-379.9 versus 1745.6+/-601.5 ml min(-1); P=0.05) and retrograde (121.7+/-43.0 versus 11.2+/-6.6 ml min(-1); P<0.001) flows were higher during FR than SR contractions, respectively. Despite the similar mean blood flow response, vascular resistance was lower during FR than SR contractions (0.06+/-0.01 versus 0.08+/-0.03 units; P=0.03) and was closely related to shear rate (pooled data: r=-0.77, P<0.01). Retrograde flow was associated with a lower vascular resistance during exercise (pooled data: r=-0.48, P<or=0.05). In addition, calculated oscillatory flow indices were higher during FR than SR contractions and were significantly correlated to retrograde flow, shear rate and vascular resistance. These results indicate that retrograde blood flow influences the shear stimulus of exercise blood flow by enhancing the oscillatory behaviour of flow.

This study examined the magnitude of the oxygen uptake slow component (VO(2) SC) during heavy exercise when preceded by heavy knee extension (KE) exercise. Nine males (26.6 +/- 1.7 years, +/-SE) performed repeated bouts of heavy exercise, each lasting 6 min with 6 min of recovery. Cycling-cycling trials (CYC(1), CYC(2)) involved step transitions to a workrate corresponding to 50% of the difference between peak VO(2) and the lactate threshold (Delta 50%). During bilateral KE-cycling trails (KE, CYC(3)), KE was performed at an intensity requiring twofold greater muscle activation relative to CYC(1) followed by a cycling transition to Delta 50%. VO(2) was measured breath-by-breath and was modeled using three exponentials to determinate the amplitudes (A (2)', A (3)') and time constants (tau (2), tau (3)) of the primary phase and VO(2) SC. Electromyography (EMG) recorded from the vastus lateralis and medialis was averaged and reported relative to maximal voluntary contraction (%MVC). EMG was higher (p < 0.05) during KE (37.6 +/- 8.1 %MVC) than CYC(1) (20.8 +/- 1.9 %MVC), CYC(2) (21.6 +/- 5.7 %MVC) and CYC(3) (19.8 +/- 6.3 %MVC). The amplitude of the VO(2) SC was lower (p < 0.05) in CYC(2) (197 +/- 120 ml min(-1)) and CYC(3) (163 +/- 51 ml min(-1)) compared to CYC(1) (325 +/- 126 ml min(-1)). No difference in VO(2) SC was observed between CYC(2) and CYC(3). Although the activation of additional motor units during KE exercise reduced the amplitude of the VO(2) SC, the decrease was similar to that observed following heavy cycling exercise. Thus, the activation of motor units in excess of those required for the activity does not alter the VO(2) response during a subsequent bout of exercise.

To test the hypothesis that sex influences forearm blood flow (FBF) during exercise, 15 women and 16 men of similar age [women 24.3 +/- 4.0 (SD) vs. men 24.9 +/- 4.5 yr] but different forearm muscle strength (women 290.7 +/- 44.4 vs. men 509.6 +/- 97.8 N; P < 0.05) performed dynamic handgrip exercise as the same absolute workload was increased in a ramp function (0.25 W/min). Task failure was defined as the inability to maintain contraction rate. Blood pressure and FBF were measured on separate arms during exercise by auscultation and Doppler ultrasound, respectively. Muscle strength was positively correlated with endurance time (r = 0.72, P < 0.01) such that women had a shorter time to task failure than men (450.5 +/- 113.0 vs. 831.3 +/- 272.9 s; P < 0.05). However, the percentage of maximal handgrip strength achieved at task failure was similar between sexes (14% maximum voluntary contraction). FBF was similar between women and men throughout exercise and at task failure (women 13.6 +/- 5.3 vs. men 14.5 +/- 4.9 ml.min(-1).100 ml(-1)). Mean arterial pressure was lower in women at rest and during exercise; thus calculated forearm vascular conductance (FVC) was higher in women during exercise but similar between sexes at task failure (women 0.13 +/- 0.05 vs. men 0.11 +/- 0.04 ml.min(-1).100 ml(-1).mmHg(-1)). In conclusion, the similar FBF during exercise was achieved by a higher FVC in the presence of a lower MAP in women than men. Still, FBF remained coupled to work rate (and presumably metabolic demand) during exercise irrespective of sex.

Muscle blood flow has been discussed as a possible factor contributing to observed sex differences in exercise tolerance. PURPOSE: To determine if forearm blood flow (FBF) is related to sex differences in exercise tolerance during dynamic forearm muscle contractions performed during a similar absolute task. METHODS: Fifteen females [24.3 ± 4.0 (SD) yr] and 16 males (24.9 ± 4.5 yr) of similar age performed intermittent handgrip exercise in a ramp function (0.5 kg-min-1) while supine with forearm at heart level. Task failure was denned as the inability to maintain contraction frequency (30 cpm) or duty cycle (0.2 s: 1.8 s). Motor unit recruitment and FBF were measured continuously during the exercise test using surface electromyography and Doppler ultrasound, respectively. RESULTS: Forearm volume was smaller (P<0.05) in females (836.9 ± 185.7 ml) than males (1291.9 ± 282.6 ml) along with isometric maximal voluntary contraction (MVC) force (F: 290.7 ± 44.4 N, M: 509.6 ± 97.8 N, P<0.05). Muscle strength was linearly related to forearm volume (pooled data, r2 = 0.79, P<0.01). Time to task failure was less for females than males (F: 450 ± 113 s, M: 831 ± 273 s, P<0.05) thus the workload achieved at task failure was greater (P<0.05) in males (M: 7.4 ±1.9 kg) than females (F: 4.2 ± 0.8 kg). However, exercise intensity achieved at task failure as a percent of their initial isometric MVC was similar between sexes (F: 14.3 ± 2.5% MVC, M: 14.2 ± 2.1 % MVC). No sex difference was found in FBF throughout forearm exercise or at task failure (F: 13.6 ± 5.3 ml-mm-1-lOOml-1, M: 14.5 ± 4.9 ml-min-l-100ml-l). In addition, the percent increase in motor unit recruitment from unloaded contractions to task failure was similar between females (425.6 ± 149.1%) and males (528.9 ± 302.9%). CONCLUSION: These findings suggest that FBF is not a contributing factor to sex differences in exercise tolerance during dynamic submaximal handgrip exercise.

Previous studies suggest that women experience less vascular occlusion than men when generating the same relative contractile force. This study examined forearm blood flow (FBF) in women and men during isometric handgrip exercise requiring the same relative force. Thirty-eight subjects [20 women and 18 men, 22.8 +/- 0.6 yrs old (means +/- SE)] performed low- and moderate-force handgrip exercise on two occasions. Subjects performed five maximum voluntary contractions (MVC) before exercise to determine 20% and 50% MVC target forces. Time to task failure (TTF) was determined when the subject could not maintain force within 5% of the target force. Mean blood velocity was measured in the brachial artery with the use of Doppler ultrasonography. Arterial diameter was measured at rest and used to calculate absolute FBF (FBFa; ml/min) and relative FBF (FBFr; ml.min(-1).100 ml(-1)). Women generated less (P < 0.05) absolute maximal force (208 +/- 10 N) than men (357 +/- 17 N). The TTF was longer (P < 0.05) at 20% MVC for women (349 +/- 32 s) than for men (230 +/- 23 s), but no difference between the sexes was observed at 50% MVC (women: 69 +/- 5 s; men: 71 +/- 8 s). FBFa and FBFr increased (P < 0.05) from rest to TTF in both women and men during 20% and 50% MVC trials. FBFr was greater in women than in men at > or =30% TTF during 50% MVC. At exercise durations > or =60% of TTF, FBFa was lower (P < 0.05) in women than in men during handgrip at 20% MVC. Despite the longer exercise duration for women at the lower contraction intensity, FBFr was similar between the sexes, suggesting that muscle perfusion is matched to the exercising muscle mass independent of sex.

During a progressive exercise test, the relationship between oxygen uptake and work rate is dependent on the slope of the ramp forcing function. It is unclear however, the extent that muscle blood flow may be affected by either fast or slow ramp exercise. PURPOSE: To examine the forearm blood flow (FBF) response to dynamic handgrip exercise during fast (FR) and slow (SR) ramp exercise to fatigue. METHODS: Six subjects (5 male and 1 female; age 28 ± 3 yrs (±sem)) performed dynamic handgrip exercise in the supine position on two separate occasions. The forcing function consisted of fast ramp (FR, 0.50 kg/min) or slow ramp (SR, 0.25 kg/min) exercise until the contraction rate (30/min) could no longer be maintained. Maximal FBF was determined by post occlusive reactive hyperemia (PORH). During exercise, FBF was measured continuously by Doppler ultrasound and expressed relative to forearm volume. Forearm flexor muscle activity was measured using surface electromyography (EMG) and analyzed in the time (iEMG, % of maximum voluntary contraction, MVC) and frequency domains (MdPF; % change from unloaded contractions). RESULTS: Fatigue was associated with a higher load and shorter exercise duration during FR (6.5 ± 0.5 kg; 686 ± 70s) than SR (5.4 ±0.4 kg; 1408 ± 143 s, p<0.05). HR and MAP increased (p<0.05) from rest to end exercise during FR and SR; no difference in HR or MAP was observed between ramp protocols. FBF was similar between FR and SR protocols at end exercise (FR, 14.1 ±1.6 ml/min/100ml; SR, 14.5 ±1.7 ml/min/100ml). FBF at end exercise, expressed as a percent of PORH, was similar between protocols (FR, 30.9 ± 4.1%; SR, 31.8 ± 4.5%) suggesting that blood flow was not limited during either FR or SR exercise. In addition, there was no difference in either iEMG (FR, 15.9 ± 3.2% MVC; SR, 12.8 ± 2.4% MVC) or MdPF (FR, −15.6 ± 5.6%; SR, −11.3 ± 4.4%) at end exercise between ramp tests. However, motor unit recruitment was closely coupled to exercise load since the ratio of iEMG to end exercise WR was similar between FR (5.3 ± 1.3) and SR(5.4± 1.3). CONCLUSION: In spite of the differences in the load and work rate achieved at fatigue during FR and SR handgrip exercise, no difference was observed between FBF, HR or MAP suggesting that the slope of the ramp forcing function does not alter cardiovascular adaptations to dynamic handgrip exercise.

At exercise intensities above the lactate threshold (LT), an additional increase in oxygen uptake (VO) of delayed onset leads to a VO that is higher than predicted from the VO2/work rate relationship for exercise below the LT. The mechanism underlying this additional O2 cost during heavy exercise (i.e. slow component, VO2 SC) is unclear. Previous studies suggest that the progressive recruitment of less-efficient type II muscle fibers may contribute to the VO2 SC. PURPOSE: To examine if the magnitude of the VO SC is altered during heavy exercise when preceded by heavy warm-up exercise involving significantly different motor unit recruitment patterns. METHODS: Nine males (26.6 ± 1.7 yrs, ±SE) performed two bouts of heavy exercise, each bout lasting 6 min with 6 min of recovery. Surface EMG was recorded from the vastus lateralis and medialis for monitoring motor unit recruitment. The sEMG signal was normalized relative to a maximum voluntary contraction obtained prior to exercise. During cyc ling-to-cyc ling trials (CYC1, CYC2) step transitions to a work rate (WR) corresponding to 50% of the difference between peak VO2 and LT (A50%) were performed. During knee extension-cyc ling trials (KE, CYC3), bilateral KE exercise was performed at an intensity that elicited twice the motor unit recruitment compared to CYC1 and followed by a single cycling transition to a WR corresponding to A50%. Pulmonary VO was measured breath-by-breath. VO was modeled using 3 exponentials for the determination of amplitudes (A2', A3') and time constants (τ2, τ3) of the primary response and VO2 SC. RESULTS: EMG was higher (p<0.05) during KE (37.6±2.7 %MVC) than CYC1 (20.8±1.9 %MVC), CYC2 (21.6±1.9 %MVC) and CYC3 (19.8±2.1 %MVC). No difference between ? or A ' was observed between CYC trials. The gain (as AVO / AWR) for the primary response was not different between CYC trials. The amplitude of the VO2 SC (A/) was lower (p<0.05) in CYC2 (197±40 ml/min) and CYC3 (163±17 ml/min) compared to CYC1 (325±42 ml/min); no difference in A3' was observed between CYC2 and CYC3. CONCLUSION: Consistent with previous studies, heavy warm-up exercise does not effect the gain or ? for the primary rise in VO during subsequent heavy exercise. The additional recruitment of presumably type II motor units during warm-up KE exercise did not alter A3' during subsequent heavy exercise differently than prior heavy cycling exercise suggesting that the additional recruitment of type II muscle fibers during warm-up exercise does not appreciably affect muscle metabolism during subsequent exercise. Funded by deArce Memorial Endowment Fund, The University of Toledo

Results from studies using animal preparations suggest that increases in muscle blood flow (MBF) are matched to the metabolic demand of the muscle rather than to the contractile work which may be contraction duration dependent. Although the effect of contraction frequency on MBF has been examined in humans such as those performed during intermittent isometric compared to dynamic exercise, the extent that differences in muscle contraction duration influences MBF and exercise tolerance has received little attention. PURPOSE: To examine the relationship between muscle blood flow and exercise tolerance during intermittent isometric and rhythmic dynamic handgrip exercise. METHODS: Nine healthy subjects (4 male, 5 female, age = 24 ±6 yrs, ± SE) participated in this study. Maximal voluntary contraction (MVC) handgrip force was determined for each subject. Brachial artery blood velocity was measured continuously during exercise using Doppler ultrasound and corrected to MBF using the diameter of the brachial artery measured at rest using 2-D Doppler imaging. Subjects performed one bout each of dynamic (DYN, 2 s concentric: 2 s eccentric) and intermittent isometric (INT, 2 s contraction; 2 s rest) handgrip exercise at 10% MVC. The timing of the contraction-relaxation cycles were designed to elicit a similar time-tension index (TTI) in DYN and INT. TTI was determined by integrating the force tracings. Exercise was performed until task failure (TTF) which was denned as the time at which the subject could no longer maintain contraction timing. RESULTS: TTF was greater (p<0.05) for the INT (878 ± 166 s) compared to DYN exercise (240 ± 27 s) which resulted in the TTI also being greater (p<0.05) for INT than DYN exercise (INT, 4129 ± 727 N-s; DYN, 950 ± 100 N-s). There was no difference in MBF at rest (DYN, 24.1 ± 6.0 ml/min; INT, 26.7 ± 9.8 ml/min). Although MBF increased (p<0.05) from rest with exercise, no difference in MBF was observed at task failure between conditions (DYN, 92.8 ± 22.4 ml/min; INT, 91.7 ± 21.9 ml/ min). When MBF was compared at an equal TTI across trials, MBF was also similar between protocols (DYN, 92.8 ± 22.4 ml/min; INT, 82.9 ± 11.3 ml/min). CONCLUSIONS: Although the TTI was similar across contraction cycles, DYN exercise resulted in considerably lower exercise tolerance compared to INT. The results of the present study indicate that MBF and presumably O2 delivery to the working muscles was similar between conditions and therefore, is not a primary determinant of exercise tolerance during handgrip exercise. Supported by deArce Memorial Endowment Fund, The University of Toledo