Proteomics of appetite-regulating system influenced by menstrual cycle and intensive exercise in female athletes: a pilot study

Female athletes who endure intense training are at risk of developing the 'female athlete triad,' making energy intake management crucial. However, the fluctuations in estradiol and progesterone levels throughout the menstrual cycle present a challenge in maintaining consistent energy intake. This study aimed to uncover the underlying factors associated with appetite regulation linked to menstrual phases and exercise using proteomic approach. Five female athletes engaged in 60 min of bicycle exercise, followed by 90 min of rest, during both the follicular and luteal phases. Serum samples were collected before, during, and after exercise, and the serum proteome was analyzed using 2D-gel electrophoresis. A total of 511 spots were detected in the subjects' serum profiles, with significant decreases observed in haptoglobin during the luteal phase and complement component 3 during bicycle training. Unsupervised learning with a generalized estimating equation analysis showed that serum peptide YY (PYY), an appetite suppressor, significantly influenced the fluctuations of serum proteins induced by exercise (p < 0.05). Regression analysis demonstrated a positive correlation between PYY and serum IgM (R = 0.87), implying that the intestinal environment and the immune response in female athletes may contribute to appetite regulation.

Effects of the menstrual cycle on EPOC and fat oxidation after low-volume high-intensity interval training

BACKGROUND

Low-volume high-intensity interval training (HIIT) for weight loss has become prevalent in recent years, with increased excess post-exercise oxygen consumption (EPOC) as the mechanism. However, the influence of the menstrual cycle on EPOC and fat oxidation following low-volume HIIT is unclear. This study aimed to investigate the effect of the menstrual cycle on the increase in EPOC and fat oxidation after low-volume HIIT.

METHODS

Twelve eumenorrheic women participated during their early follicular and luteal phases. On each experimental day, they performed low-volume HIIT comprising fifteen repeated 8 s sprint cycling tests with 12 s rests, for 5 min. Expired gas samples were collected before and every 60 min until 180 min post-exercise. EPOC was defined as the increase in oxygen consumption from the resting state, and the total EPOC and fat oxidation were calculated from the total time of each measurement. Blood samples for serum estradiol, progesterone, free fatty acids, blood glucose, lactate, and plasma noradrenaline were collected and assessed before immediately after, and at 180 min post-exercise and were assessed.

RESULTS

Serum estradiol and progesterone were significantly higher in the luteal phase than the follicular phase (P<0.01 for both). No significant differences in total EPOC and fat oxidation were found between the menstrual phases. Serum free fatty acid, blood glucose, lactate, and plasma noradrenaline concentrations were not affected by the menstrual cycle.

CONCLUSIONS

These results suggest that the menstrual cycle does not affect the increase in EPOC or fat oxidation after low-volume HIIT.

Effects of acute aerobic exercise on arterial stiffness in transgender men

Testosterone replacement therapy (TRT) in transgender men (TM) results in side effects such as elevated triglycerides and increased arterial stiffness. Exercise may be useful to ameliorate such effects, but no studies have examined the effects of acute aerobic exercise in TM. This study aimed to investigate the effects of acute aerobic exercise on arterial stiffness in TM. Thirty-six participants were included, comprising 12 TM (duration of TRT: 57.4 ± 30.3 months), 12 males and 12 females. All participants performed acute aerobic exercise on a treadmill at 50% heart rate reserve for 30 min. Arterial stiffness as measured by brachial-ankle pulse wave velocity (baPWV) was measured before exercise (Pre), 30 min after exercise (Post30), and 60 min after exercise (Post60). Serum sex hormone levels, and serum lipid profile were determined only before exercise. Serum low-density lipoprotein cholesterol (LDL-C) levels before exercise were significantly higher in TM than in males or females (males: p < 0.01; females: p < 0.05). At all points, baPWV in TM was significantly higher than in females (p < 0.05) and significantly lower than in males (p < 0.05). However, when comparing changes in baPWV over time in each group, significant decreases in Post30 and Post60 were seen in males compared to Pre (both p < 0.05), but no significant change after aerobic exercise was seen in TM or females. These results suggest that acute aerobic exercise yield different effects in TM than in males, but is unlikely to reduce arterial stiffness in TM receiving TRT.

Influence of the Menstrual Cycle on Muscle Glycogen Repletion After Exhaustive Exercise in Eumenorrheic Women

ABSTRACT

Matsuda, T, Takahashi, H, Nakamura, M, Ogata, H, Kanno, M, Ishikawa, A, and Sakamaki-Sunaga, M. Influence of the menstrual cycle on muscle glycogen repletion after exhaustive exercise in eumenorrheic women. J Strength Cond Res 37(4): e273-e279, 2023-The purpose of this study was to investigate the effect of the menstrual cycle on muscle glycogen repletion postexercise. Eleven women with regular menstrual cycles (age: 20.2 ± 1.3 years, height: 161.1 ± 4.8 cm, and body mass: 55.5 ± 5.7 kg) were assessed in 3 phases of the cycle: the early follicular phase (E-FP), late follicular phase (L-FP), and luteal phase (LP). Each test day began with glycogen-depleting exercise, followed by 5 hours of recovery. Muscle glycogen concentrations, using 13 C-magnetic resonance spectroscopy, and estradiol, progesterone, blood glucose, blood lactate, free fatty acid (FFA), and insulin concentrations were measured at t = 0, 120, and 300 minutes postexercise. During the 5-hour recovery period, subjects consumed 1.2g·(kg body mass) -1 ·h -1 of carbohydrates every 30 minutes. The muscle glycogen concentrations increased at t = 120 and t = 300 minutes postexercise ( p < 0.01) but were not significantly different between the menstrual cycle phases ( p = 0.30). Blood lactate concentrations were significantly higher in the L-FP and LP than in the E-FP ( p < 0.05). Nonetheless, the blood glucose, FFA, insulin concentrations, and the exercise time until exhaustion in the E-FP, L-FP, and LP were similar (blood glucose, p = 0.17; FFA, p = 0.50; insulin, p = 0.31; exercise time, p = 0.67). In conclusion, the menstrual cycle did not influence muscle glycogen repletion after exercise.

Does resistance exercise lifting velocity change with different rest intervals?

BACKGROUND

In this study, we examined the sex difference of the effect of rest intervals on lifting velocity during resistance exercise.

METHODS

Twenty-two trained subjects (11 men and 11 women) were included. Each protocol consisted of 3 sets of 10 repetitions at 70% of 1- repetition maximum (1RM) with rest intervals of 90 s (R90), 150 s (R150), and 240 s (R240) in a crossover design. The exercise did parallel squats with free weights. The measurement items are lifting velocity (mean velocity) in each repetition and blood lactate concentration after exercise.

RESULTS

There was a significant interaction between changes in the average velocity of 10 repetition in each set (AV<inf>10rep</inf>) and sex in each protocol, indicating that AV<inf>10rep</inf> during squat exercise has decreased in men but not in women in each protocol (P=0.002-0.03).

CONCLUSIONS

Our results suggested that short rest intervals will not recover lifting velocity between short rest intervals until the next set at men, while women will be able to recover even with short rest intervals.

Influence of menstrual cycle on muscle glycogen utilization during high-intensity intermittent exercise until exhaustion in healthy women

The present study investigated the effects of the menstrual cycle on muscle glycogen and circulating substrates during high-intensity intermittent exercise until exhaustion in healthy women who habitually exercised. In total, 11 women with regular menstrual cycles completed three tests, which comprised the early follicular phase (E-FP), late follicular phase (L-FP), and luteal phase (LP) of the menstrual cycle. High-intensity intermittent exercise until exhaustion was performed on each test day. Evaluation of muscle glycogen concentration by ¹³C-magnetic resonance spectroscopy and measurement of estradiol, progesterone, blood glucose, lactate, free fatty acids (FFA), and insulin concentrations were conducted before exercise (Pre) and immediately after exercise (Post). Muscle glycogen concentrations from thigh muscles at Pre and Post were not significantly different between menstrual cycle phases (P = 0.57). Muscle glycogen decreases by exercise were significantly greater in L-FP (59.0 ± 12.4 mM) than in E-FP (48.3 ± 14.4 mM, P < 0.05). Nonetheless, blood glucose, blood lactate, serum FFA, serum insulin concentrations, and exercise time until exhaustion in E-FP, L-FP, and LP were similar. The study results suggest that although exercise time does not change according to the menstrual cycle, the menstrual cycle influences muscle glycogen utilization during high-intensity intermittent exercise until exhaustion in women with habitual exercise activity. Novelty: This study compared changes in muscle glycogen concentration across the menstrual cycle during high-intensity intermittent exercise until exhaustion using ¹³C-magnetic resonance spectroscopy. Our results highlight the influence of the menstrual cycle on muscle glycogen during high-intensity intermittent exercise in healthy women.

The Effect of Co-Ingestion of Carbohydrate with Milk after Exercise in Healthy Women: Study Considering the Menstrual Cycle

This study aimed to assess the effects of co-ingestion of carbohydrate with milk (MILK) and isocaloric carbohydrate beverage (CHO) on post-exercise recovery and subsequent exercise capacity, considering the menstrual cycle. This study included 12 women with regular menstrual cycles who completed four test days, which started with glycogen-depleting exercise using a cycle ergometer in the early follicular phase (EF) and late follicular phase (LF), followed by 240 min of recovery from the ingestion of 200 mL of CHO or MILK every 30 min immediately after the exercise (POST0) until 210 min post-exercise. After 240 min, participants performed an exercise capacity test. Blood samples and breathing gas samples were collected before the exercise (PRE), POST0, and 120 (POST120) and 240 min after the end of exercise (POST240) to determine the concentrations of estradiol, progesterone, blood glucose, blood lactate, free fatty acid (FFA), and insulin and the respiratory exchange ratio, fat oxidation, and carbohydrate oxidation. The exercise time at exercise capacity test was not significantly different in terms of menstrual cycle phases and recovery beverages ingested. However, there was a significant positive correlation between the exercise capacity test and area under the curve (AUC) of FFA concentrations from POST0 to POST240 in each group (EF + CHO, p < 0.05; LF + CHO, p < 0.05; EF + MILK, p < 0.01; and LF + MILK, p < 0.05). The AUC of FFA from POST120 to POST240 showed no difference between EF (CHO and MILK) and LF (CHO and MILK). However, the AUC of FFA concentrations from POST120 to POST240 was significantly greater in MILK (EF and LF) than that in CHO (EF and LF) (p < 0.05). In active women, circulating substrates and hormone concentrations during short recovery post-exercise are not affected by the menstrual cycle. However, MILK may affect circulating substrates during recovery and the exercise capacity after recovery.

Effects of menstrual cycle on appetite-regulating hormones and energy intake in response to cycling exercise in physically active women

Although ample evidence supports the notion that an acute bout of endurance exercise performed at or greater than 70% of maximum oxygen uptake suppresses appetite partly through changes in appetite-regulating hormones, no study has directly compared the influence between the phases of the menstrual cycle in women. The present study compared the effects of an acute bout of exercise on orexigenic hormone (acylated ghrelin) and anorexigenic hormones (peptide YY and cholecystokinin) between the early follicular phase (FP) and the mid luteal phase (LP) of the menstrual cycle in physically active women. Ten healthy women (age, 20.6 ± 0.7 years) completed two 3.5-h trials in each menstrual phase. In both trials, participants performed cycling exercises at 70% of heart rate reserve (at a corresponding intensity to 70% of maximum oxygen uptake) for 60 min followed by 90 min of rest. Following 90 min of rest, participants were provided with an ad libitum meal for a fixed duration of 30 min. Blood samples and subjective appetite were collected and assessed before, during, immediately post-, 45 min post-, and 90 min post-exercise. The exercise increased estradiol (327 %) and progesterone (681 %) in the LP more than the FP respectively (P < 0.001, f = 1.33; P < 0.001,f = 1.20). There were no between-trial differences in appetite-regulating hormones, subjective appetite, or energy intake of ad libitum meal. These findings indicate that exercise-induced increases in ovarian hormones in the LP may not influence appetite-regulating hormones in physically active women.

Relationship between weight management and menstrual status in female athletes: a cross-sectional survey

The aim of this study was to investigate the effects of weight management on menstrual status in female athletes. A total of 225 collegiate athletes and 27 para-athletes who belonged to teams affiliated with the Japanese Paralympic Committee were included in this cross-sectional survey. A self-reported questionnaire (containing information on the demographic characteristics, medical history, lifestyle habits, weight management, menstruation status, physical symptoms related to menstrual cycle, and the influence of physical symptoms experienced during the luteal phase of menstruation during training or competition.) was used to assess the results. In the collegiate athletes, the rate of regular menstrual cycle was significantly lower in those with weight loss than in those without (56.7% vs. 75.0%, P < .05). Furthermore, stress fractures were found significantly more often in those with weight loss than those without (36.1% vs. 20.3%, P < .05). In the para-athletes, 46.2% of experience in weight loss had irregular menstruations (P < .01), and all of them had physical symptoms that negatively affected their training or competition (P < .05). To prevent menstrual dysfunction related to energy deficiency in female athletes with weight management, menstrual status must be considered.

Effects of the menstrual cycle on oxidative stress and antioxidant response to high-intensity intermittent exercise until exhaustion in healthy women

BACKGROUND

This study aimed to investigate the effects of the menstrual cycle on the oxidative stress and antioxidant response during high-intensity intermittent exercise until exhaustion in healthy women who habitually exercised.

METHODS

Ten women with normal menstrual cycle completed 2 menstrual cycle phases, including the early follicular phase (FP) and the midluteal phase (LP). High-intensity exercise until exhaustion was performed on each test day. Blood samples were collected before the exercise (Pre), immediately after the exercise (Post0), and 60 minutes after the exercise (Post60). The levels of estradiol; progesterone; oxidative stress, which was measured as diacron reactive oxygen metabolites (d-ROMs); and antioxidant capacity, which was measured as the biological antioxidant potential (BAP), were assessed.

RESULTS

The levels of serum estradiol and progesterone at Pre were significantly higher in the LP than in the FP (P<0.01). There were no significant differences in the d-ROMs, BAP, and BAP/d-ROMs between the FP and the LP at Pre, Post0, and Post60. Compared with the FP, the LP had significantly lower d-ROMs change rate from Pre at Post0 and Post60 (P<0.05). Moreover, the BAP/d-ROMs change rate from Pre showed a significantly higher trend in the LP than in the FP at Post0 and Post60 (P=0.06).

CONCLUSIONS

In women with regular menstrual cycle, oxidative stress during exercise and recovery may be eliminated during the LP, when the estradiol and progesterone levels are higher, compared with those during the FP.

Effects of the Menstrual Cycle on Serum Carnitine and Endurance Performance of Women

This study aimed to investigate the effect of the menstrual cycle on serum carnitine and the endurance performance of healthy women. Fifteen eumenorrheic women underwent cycle ergometer exercise at 60% maximal oxygen uptake (V̇ O_2max) for 45 min, followed by exercise at an intensity that was increased to 80% V̇ O _2max until exhaustion, during two menstrual cycle phases, including the early follicular phase (FP) and the midluteal phase (LP). The blood levels of estradiol, progesterone, total carnitine, free carnitine, and acylcarnitine were assessed. Compared with the FP, the LP had significantly lower serum total carnitine (p<0.05) and free carnitine (p<0.01). Moreover, the group with decreased endurance performance in the LP than in the FP showed a significantly higher change in serum free carnitine compared with the group that showed improved endurance performance in the LP than in the FP (p<0.05). The results of this study suggested that the changes in serum free carnitine during the menstrual cycle might influence endurance performance.

Acute Effect of Interval Walking on Arterial Stiffness in Healthy Young Adults

The purpose of this study was to determine the acute effects of interval walking (IW) on arterial stiffness. The participants in this study were 14 healthy men and women (age 27.5±3.8 y). Carotid-femoral pulse wave velocity (cfPWV) was measured using an automatic oscillometric device at 30 min before (baseline) and at 30 and 60 min after walking. Participants repeated five sets of 3-min walks at 30% and 70% of maximum aerobic capacity for a total of 6 min per set in the IW trial. The participants also walked for 30 min at 50% (moderate intensity) of maximum aerobic capacity in a continuous walking (CW) trial. cfPWV was significantly decreased from baseline at 30 min (P=0.02) after the IW trial, and this reduction in cfPWV persisted for 60 min (P=0.01). In contrast, cfPWV was significantly decreased from baseline at 30 min (P=0.03) after the CW trial, but the reduction did not persist for 60 min. Moreover, changes in cfPWV in the IW trial after 30 and 60 min were significantly lower than in the CW trial (P<0.05). These results suggest that IW acutely reduces central arterial stiffness more than CW in healthy young adults.

Effect of Resistance Exercise on Arterial Stiffness during the Follicular and Luteal Phases of the Menstrual Cycle

Acute high-intensity resistance exercise increases arterial stiffness. Changes in blood concentrations of estrogen and progesterone associated with the menstrual cycle affect the degree of arterial stiffness. Therefore, high-intensity resistance exercise may affect arterial stiffness differently depending on the phase of the menstrual cycle. The purpose of this study was to investigate the effects of different phases of the menstrual cycle on arterial stiffness after one session of resistance exercise. The participants were 9 eumenorrheic females (21.3±0.8 years). All participants performed 5 sets of 5 repetitions using 80% of the one repetition maximum (1RM) bench press and 5 sets of 10 repetitions using 70% of the 1RM biceps curl during both the follicular and luteal phases. Brachial-ankle pulse wave velocity (baPWV), blood pressure, and heart rate were measured before (baseline) and at 30 and 60 min after completing the resistance exercises. During the follicular phase, baPWV was significantly increased at 30 and 60 min after the resistance exercise compared with baseline (P<0.05), whereas during the luteal phase, no significant differences were observed after the resistance exercise. These results suggest that high-intensity resistance exercise affects arterial stiffness differently depending on the phase of the menstrual cycle.

Effects of Menstrual Phase-Dependent Resistance Training Frequency on Muscular Hypertrophy and Strength

The present study investigated how different training frequencies during menstrual phases affect muscle hypertrophy and strength. Fourteen eumenorrheic women performed 3 sets of arm curls (8-15 repetitions) until failure for 12 weeks. Depending on the menstrual cycle phase, each subject trained each arm separately after either a 3- or a 1-d·wk training protocol during the follicular phase (FP-T) and a 3- or 1-d·wk training protocol during the luteal phase (LP-T). Cross-sectional area (CSA), 1 repetition maximum, and maximum voluntary contraction significantly increased 6.2 ± 4.4, 36.4 ± 11.9, and 16.7 ± 5.6%, respectively (p ≤ 0.05 vs. before training), in the FP-T group and 7.8 ± 4.2, 31.8 ± 14.1, and 14.9 ± 12.7%, respectively (p ≤ 0.05 vs. before training), in the LP-T group. Changes in CSA between the FP-T and the LP-T groups significantly and positively correlated (r = 0.54, p ≤ 0.05). There were no major differences among the different training protocols with regard to muscle hypertrophy and strength. Therefore, we suggest that variations in female hormones induced by the menstrual cycle phases do not significantly contribute to muscle hypertrophy and strength gains during 12 weeks of resistance training.

The ACTN3 R577X genotype is associated with muscle function in a Japanese population

Homozygosity for the common nonsense polymorphism R577X in the α-actinin-3 gene (ACTN3) causes complete α-actinin-3 deficiency in fast-twitch skeletal muscle fibers. This study investigated whether the ACTN3 R577X polymorphism affects fitness status using a battery of tests in a large Japanese cohort. In the present study, 1227 subjects (age: 25-85 years) were genotyped for the ACTN3 R577X polymorphism (rs1815739) using a TaqMan SNP genotyping assay (Applied Biosystems). All subjects were divided into 2 groups based on their age (<55 years and ≥55 years). All subjects completed a questionnaire about exercise habits and were subjected to a battery of tests to assess their fitness status (including grip strength test, chair stand test, and 8-foot walking test). A significant association between the ACTN3 R577X genotype and chair stand test performance was observed in the group of men ≥55 using ANCOVA adjusted for age and exercise habits (p = 0.036). The ACTN3 R577X genotype accounted for 2.5% of the variability in the results of the chair stand test among men in the ≥55 age group. Moreover, for the ≥55 age group, performance in the chair stand test was lower among those with the XX genotype than among those with the RR genotype (p = 0.024) or RX genotype (p = 0.005), unlike results for the <55 age group. No significant difference was noted for hand grip strength or 8-foot walking time. Thus, our results suggest that the ACTN3 R577X genotype is associated with lower-extremity muscle function in the Japanese population.

Arterial compliance and stiffness following low-intensity resistance exercise

PURPOSE

Although acute high-intensity resistance exercise to exhaustion decreases arterial compliance and increases arterial stiffness, the effect of low-intensity resistance exercise (LRE) to exhaustion on arterial compliance and stiffness remains unknown. The present study investigated the acute effects of LRE on arterial compliance and stiffness.

METHODS

Ten healthy individuals (age 26 ± 5 years) performed LRE (40% of 1 repetition maximum) and control (CON: seated rest in the exercise room) trials on separate days in a randomized controlled crossover fashion. The LRE comprised three sets of bench presses to exhaustion with an inter-set rest period of 2 min. In the CON trial, LRE was not performed. Carotid arterial compliance, the β-stiffness index (via simultaneous B-mode ultrasound and applanation tonometry), carotid and brachial blood pressure and heart rate were measured before and at 30 and 60 min after both trials.

RESULTS

Carotid arterial compliance and the β-stiffness index significantly increased and decreased, respectively (both P < 0.05), at 30 and 60 min after the LRE trials, but neither significantly differed after the CON trials. Carotid and brachial blood pressure and heart rate did not change at 30 and 60 min after both trials from baseline.

CONCLUSION

These results suggest that LRE acutely increases arterial compliance and decreases arterial stiffness.

Acute effect of brisk walking with graduated compression stockings on vascular endothelial function and oxidative stress

The purpose of this study was to investigate the acute effect of brisk walking with and without graduated compression stockings (GCSs) on vascular endothelial function and oxidative stress. Ten young healthy subjects walked briskly for 30 min with (GCS trial) and without (CON trial) GCSs in a randomized crossover trial. Brachial artery flow-mediated dilation (FMD) was measured as the per cent rise in the peak diameter from the baseline value at prior occlusion at each FMD measurement using B-mode ultrasonography before and 30 min after walking in the two trials. Derivatives of reactive oxygen metabolites (d-ROM), as an index of products of reactive oxygen species, and biological anti-oxidant potential (BAP), as an index of anti-oxidant potential, were also measured using a free radical elective evaluator before and 30 min after walking in both trials. FMD significantly decreased after brisk walking in both trials (P<0·05). However, FMD after brisk walking in the GCS trial was significantly higher than that in the CON trial (P<0·05). The d-ROM did not change before and after both trials, whereas the BAP significantly increased after walking in the GCS trial (P<0·05). These findings demonstrate that brisk walking while wearing GCSs suppresses the decrease in FMD and increases BAP.

Effects of high-intensity and blood flow-restricted low-intensity resistance training on carotid arterial compliance: role of blood pressure during training sessions

We examined the effects of high-intensity resistance training (HIT) and low-intensity blood flow-restricted (LI-BFR) resistance training on carotid arterial compliance. Nineteen young men were randomly divided into HIT (n = 9) or LI-BFR (n = 10) groups. The HIT and LI-BFR groups performed 75 and 30 %, respectively, of one-repetition maximum (1-RM) bench press exercise, 3 days per week for 6 weeks. During the training sessions, the LI-BFR group wore elastic cuffs around the most proximal region of both arms. Muscle cross-sectional area (CSA), 1-RM strength, and carotid arterial compliance were measured before and 3 days after the final training session. Acute changes in systolic arterial pressure (SAP), plasma endothelin-1 (ET-1), nitrite/nitrate (NOx), and noradrenalin concentrations were also measured during and after a bout of training session. The training led to significant increases (P < 0.01) in bench press 1-RM and arm and chest muscle CSA in the two training groups. Carotid arterial compliance decreased significantly (P < 0.05) in the HIT group, but not in the LI-BFR group. There was a significant correlation (r = -0.533, P < 0.05) between the change in carotid arterial compliance and the acute change in SAP during training sessions; however, ET-1 and NOx did not correlate with carotid arterial compliance. Our results suggest that muscle CSA and strength increased following 6 weeks of both HIT and LI-BFR training. However, carotid arterial compliance decreased in only the HIT group, and the changes were correlated with SAP elevations during exercise sessions.

Onset of blood lactate accumulation and peak oxygen uptake during graded walking test combined with and without restricted leg blood flow

The purpose of this study was to compare the peak oxygen uptake (VO2peak) and lactate threshold / onset of blood lactate accumulation (LT/OBLA) during an incremental exercise test with and without blood flow restriction (BFR). Six male subjects performed a graded walking test on a treadmill with and without BFR in random order, and oxygen uptake (VO2), minute ventilation (VE), and blood lactate concentration were measured during each test. During the BFR test, the subjects wore pressure cuff belts on the most proximal portion of each thigh. At a given workload (e.g. during walking at 100 m/min) VO2 was 17% higher in BFR than in free-flow. Exercise time to exhaustion during BFR was shorter compared with free-flow despite the ratings of perceived exertion being similar between both conditions. Peak heart rate did not reach same level in the BFR test as it did in free-flow, with the heart rate 5 beats lower with BFR. VO2peak and VE peak were also 17% and 9%, respectively, lower in BFR than in free-flow. Compared with the control, O2 pulse (an index of stroke volume) was 14% lower in BFR. During BFR, VO2 at LT and OBLA were lower compared with free-flow. However, percentages of VO2peak at LT and OBLA were similar between BFR and free-flow. Our results suggest that the BFR-induced decrease in VO2peak may be associated with reductions in venous return and stroke volume. Additionally, these results suggest that increased muscle fiber recruitment with BFR may relate to the earlier LT/OBLA observed at lower intensities.