Effects of Sex and Cuff Pressure on Physiological Responses during Blood Flow Restriction Resistance Exercise in Young Adults

Skeletal Muscle Resaturation Relates to Aerobic Fitness in Adults Participating in Strength and Aerobic Exercises

Purpose: This study examined differences in metrics of skeletal muscle re-saturation between strength and aerobically oriented individuals and potential relations between re-saturation and aerobic fitness. Methods: Forty-nine healthy young adult men and women completed body composition analysis, a maximal lower-body strength assessment, a maximal aerobic fitness (V . O 2 max ) test, and a near-infrared spectroscopy vascular occlusion test (NIRS+VOT). Skeletal muscle tissue oxygenation (StO2), oxygenated hemoglobin (O2Hb), and deoxygenated (HHb) hemoglobin were collected from a NIRS device attached to the vastus lateralis. Re-saturation measures (e.g. upslope, re-saturation max, and hypersaturation area under the curve (AUC)) were derived from the reperfusion phase of the NIRS+VOT. Results: All O2Hb and StO2 re-saturation metrics, particularly upslope (r = 0.622 and r = -.613, respectively), were significantly (p < .05) related to V . O 2 max . In the strength group, O2Hb and HHb upslope (r = 0.584; p < .001; r = -.550; p = .001, respectively) and re-saturation max (r = 0.372; p = .036; r = .562, p < .001, respectively) were significantly related to V . O 2 max . For the aerobic group, O2Hb upslope (r = .486; p = .048), re-saturation max (r = 0.535; p = .027), and hypersaturation AUC (r = 0.564; p = .018) were significantly related to V . O 2 max . The aerobic group had significantly (p = .011; BF10 = 8.043) greater O2Hb upslope (1.6 ± .789 vs. 1.1 ± .474 A.U.s-1) and (p = .027; BF10 = 2.929) hypersaturation AUC (1158.3 ± 545.02 vs. 860.4 ± 365.35 A.U.s-1) than the strength group. Conclusion: Upslope was the most related to V . O 2 max in strength and aerobically oriented adults. Interestingly, O2Hb re-saturation max may not be sensitive to differences between routine strength and aerobic exercise and may reflect shared underlying physiological mechanisms of the predominant fitness orientation.

Physiological Sensor Modality Sensitivity Test for Pain Intensity Classification in Quantitative Sensory Testing

Chronic pain is prevalent and disproportionately impacts adults with a lower quality of life. Although subjective self-reporting is the "gold standard" for pain assessment, tools are needed to objectively monitor and account for inter-individual differences. This study introduced a novel framework to objectively classify pain intensity levels using physiological signals during Quantitative Sensory Testing sessions. Twenty-four participants participated in the study wearing physiological sensors (blood volume pulse (BVP), galvanic skin response (GSR), electromyography (EMG), respiration rate (RR), skin temperature (ST), and pupillometry). This study employed two analysis plans. Plan 1 utilized a grid search methodology with a 10-fold cross-validation framework to optimize time windows (1-5 s) and machine learning hyperparameters for pain classification tasks. The optimal time windows were identified as 3 s for the pressure session, 2 s for the pinprick session, and 1 s for the cuff session. Analysis Plan 2 implemented a leave-one-out design to evaluate the individual contribution of each sensor modality. By systematically excluding one sensor's features at a time, the performance of these sensor sets was compared to the full model using Wilcoxon signed-rank tests. BVP emerged as a critical sensor, significantly influencing performance in both pinprick and cuff sessions. Conversely, GSR, RR, and pupillometry demonstrated stimulus-specific sensitivity, significantly contributing to the cuff session but with limited influence in other sessions. EMG and ST showed minimal impact across all sessions, suggesting they are non-critical and suitable for reducing sensor redundancy. These findings advance the design of sensor configurations for personalized pain management. Future research will focus on refining sensor integration and addressing stimulus-specific physiological responses.

Hemodynamic analysis of blood flow restriction training: a systematic review

Blood Flow Restriction Training (BFRT) is a low-load training technique that involves applying pressure to partially restrict arterial blood flow while occluding venous return. Despite its growing popularity, there is still no consensus on how combining BFRT with resistance or aerobic training influences hemodynamic responses, or on the safest and most effective methods for implementing it. This review aims to systematically identify the effects of BFRT on hemodynamic parameters. A systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement guidelines. The Chinese literature search was performed in the China National Knowledge Infrastructure (CNKI) database. English literature search was conducted in the Web of Science, PubMed, and Google Scholar databases. The studies included human subjects, the outcome indicators included hemodynamic evaluation indicators, and only randomized controlled trials and randomized crossover trials were considered. Non-Chinese or English literature, duplicate studies, and those with missing data were excluded. The adapted STROBE checklist was used to assess the risk of bias, 44 articles were included in this review. Results indicated that BFRT has increased heart rate and blood lactate levels, while its effect on blood oxygen saturation varies. Additionally, BFRT significantly enhances cardiac output but may either have no significant effect or cause a decrease in stroke volume. Furthermore, BFRT improves pulse wave velocity from the femur to the posterior tibia, suggesting a positive influence on cardiovascular function. BFRT induces changes in arterial structure and function, with these indicators interacting to produce both positive and negative effects on cardiovascular health. The primary mechanisms by which BFRT influences hemodynamics include the activation of the sympathetic and vagus nerves, as well as the regulation of chemical mediators in body fluids that modulate cardiovascular function. Convenient, economical, non-invasive, and easily measurable hemodynamic indicators are expected to become an efficient tool for evaluating the effects of exercise training. Further research is needed to establish the optimal compression thresholds and durations for different populations and exercise types, as well as to assess the long-term impact of BFRT on hemodynamic parameters.

Blood flow restriction during high load bench press does not increase bar velocity or cause physiological changes in non-occluded agonist muscles

PURPOSE

Blood blow restriction (BFR) can increase peak velocity and power during high load resistance training. However, previous research primarily utilized high occlusion pressures (i.e., greater than 80% arterial occlusion pressure (AOP)), and rarely measured the physiological response during or after the bench press stimuli. The aim of this study was to investigate the application of 50%AOP during acute high load bench press exercise on barbell power, velocity, and the physiological responses to this stimulus.

METHODS

Resistance trained males (n = 12, 26.2 ± 6.6 yrs., 84.0 ± 10.8 kg, 176.3 ± 10.4 cm) completed a maximum strength test followed by two experimental sessions which consisted of four sets of 4 reps of the barbell bench press at 75%1RM, with or without BFR applied to both arms at 50% AOP. Significance was set to p ≤ 0.05. A series of two-way repeated measures ANOVAs with Bonferroni post hoc corrections tested for potential changes in bar velocity, power, blood lactate, and muscle thickness and activation of the anterior deltoid and pectoralis major.

RESULTS

There were no main effects for the interaction terms "Condition×Set" or "Condition×Time," nor for "Condition" for any variables (all p > 0.05). There was a "Time" effect for blood lactate (p < 0.001) with lactate increasing from pre- to postexercise, and a main effects for "Set" for mean (p = 0.016) and peak velocity (p = 0.005).

CONCLUSION

There was no difference in the change in velocity, or physiological responses during high load bench press with or without BFR at 50%AOP. While promising, use of BFR for upper body power may require pressures >50%AOP.

Tissue oxygenation in response to low-load and high-load back squats with continuous blood flow restriction in athletes

To determine muscle oxygenation with continuous blood flow restriction (BFR) training in high load (HL), 80% one-repetition maximum (1RM) and low load (LL), 30% 1RM squat exercises. In week-2 of a 4-week resistance training programme as part of their 3-set training routine, two groups of athletes (n = 4 each), one performing HL training with low cuff pressure (20% arterial occlusion pressure (AOP)), the other LL training with high cuff pressure (60% AOP) had muscle oxygenation assessed with near-infrared spectrophotometry (NIRS), arterial oxygen saturation (SPO2), heart rate (HR), barbell velocity and ratings of perceived exertion (RPE) during barbell back squats (BBS). Changes in the vastus lateralis oximetry were compared to pre- and post-training squat (1RM). Across athletes, there were significant associations between two pre-set-3 exercise variables and post-training 1RM, Tissue Saturation Index (TSI) (R2 = 0.92, p < 0.0002) and HHb concentration (R2 = 0.79, p < 0.003). Generalised regression models indicated that TSI % and HHb concentrations before and after set 3 timepoints were significant predictors of post-training 1RM in the LL group (R2 = 0.99, BIC = -24.9). Well-tolerated continuous LL-BFR training provided greater increases in strength than HL-BFR in athletes.

Salivary testosterone and cortisol responses to seven weeks of practical blood flow restriction training in collegiate American football players

Purpose

The purpose of this study was to examine the effects of a 7-week supplemental BFR training intervention on both acute and chronic alterations in salivary testosterone (sTes) and cortisol (sCort) in collegiate American football players.

Methods

58 males were divided into 4 groups: 3 completed an upper- and lower-body split resistance training routine (H, H/S, H/S/R; H = Heavy, S = Supplemental, R = BFR), with H/S/R performing end-of-session practical BFR training, and H/S serving as the volume-matched non-BFR group. The final group (M/S/R) completed modified resistance training programming with the same practical BFR protocol as H/S/R. Athletes were further split into AM and PM training groups based upon their pre-determined training schedules, in cooperation with University strength and conditioning staff. Practical BFR consisted of end-of-session barbell bench press and back squat using 20% 1 repetition maximum (1RM) for 30-20-20-20 repetitions across 4 sets, with 45-seconds rest. Saliva samples were taken pre- and post- the first lower-body training sessions in week 1 and week 7 (i.e., test 1 and test 2) of the program, yielding four total. sTes and sCort were analyzed using 4-way (4 × 2 × 2 × 2) mixed model ANOVA's.

Results

Hormonal variables all exhibited main effects for time-of-day (p < 0.001). A significant group × time interaction effect (F3,50 = 3.246, p < 0.05) indicated increases in sTes post-training cycle for the H/S/R group only. Further, PM post-exercise sCort decreased from test 1 to test 2 (nmol·L-1: 95% CI: PM test 1 post-exercise = 10.7-17.1, PM test 2 post-exercise = 5.0-8.9). For the testosterone-to-cortisol ratio (T/C), AM pre-exercise was lower than PM (p < 0.05), with no change in post-exercise T/C for both AM and PM conditions when collapsed across testing times.

Discussion

Overall, these findings suggest an ecologically valid method of BFR implementation is capable of inducing heightened concentrations of sTes in well-resistance trained American football athletes, providing additional insight on possible physiological mechanisms underpinning BFR's ability to elicit beneficial muscle hypertrophy and maximal strength adaptations when performed during regimented training programs. Additionally, notable rises in T/C, and a null sCort response post-exercise were observed post-program for all groups, possibly indicative of positive physiological adaptation.

Blood flow restriction increases motor unit firing rates and input excitation of the biceps brachii during a moderate-load muscle action

This study examined the effects of blood flow restriction (BFR) on motor unit (MU) behaviour of the biceps brachii (BB) during a single non-exhausting submaximal muscle action. Twenty adults performed maximal voluntary contractions (MVCs) of the elbow flexors, followed by an isometric trapezoidal muscle action at 40% MVC during BFR and control (CON) visits. Surface electromyographic signals recorded from the BB during the 40% MVCs were decomposed. Recruitment thresholds (RTs), MU action potential amplitudes (MUAPAMPS), initial firing rates (IFRs), mean firing rates (MFRs) at steady force, and normalized EMG amplitude (N-EMGRMS) were analysed. Y-intercepts and slopes were calculated for the MUAPAMP, IFR, and MFR vs. RT relationships. Y-intercepts for the IFR and MFR vs. RT relationships and N-EMGRMS increased during BFR (p < 0.05) collapsed across sex. The slopes for the IFR and MFR vs. RT relationships decreased during BFR (p < 0.05) collapsed across sex. The y-intercepts and slopes for the MUAPAMP vs. RT relationships were not different (p > 0.05) between treatments or sex. BFR during the 40% MVC increased IFRs, MFRs, and N-EMGRMS. However, the similar MUAPAMPS observed between treatments may suggest that a greater load is necessary to recruit additional MUs when performing a single submaximal short-duration muscle action with BFR.

Effects of occlusion pressure on hemodynamic responses recorded by near-infrared spectroscopy across two visits

Ischemic Preconditioning (IPC) has emerged as a promising approach to mitigate the impact of hypoxia on physiological functions. However, the heterogeneity of occlusion pressures for inducing arterial occlusion has led to inconsistent hemodynamic outcomes across studies. This study aims to evaluate the peripheral hemodynamic responses to partial and total blood-flow occlusions on the left arm at rest, using absolute or individualized pressures, on two occasions. Thirty-five young males volunteered to participate in this study. IPC procedure (3 × 7-min) was performed on the left upper arm with cuff pressures at 50 mmHg (G1), 50 mmHg over the systolic blood pressure (SBP + 50 mmHg) (G2) or 250 mmHg (G3). NIRS-derived parameters were assessed for each occlusion and reperfusion phase in the brachioradialis. Results showed a significantly lower magnitude of deoxygenation (TSIAUC) for G1 compared to G2 (-1959.2 ± 1417.4 vs. -10908.1 ± 1607.5, P < 0.001) and G3 -1959.2 ± 1417.4 vs. -11079.3 ± 1828.1, P < 0.001), without differences between G2 and G3. However, G3 showed a significantly faster reoxygenation only for tissue saturation index (TSIslope) compared to G2 (1.3 ± 0.1 vs. 1.0 ± 0.2, P = 0.010), but without differences in the speed of recovery of deoxyhemoglobin [(HHb) slope], or in the magnitude of post-occlusive hyperemia (PORH). Besides TSI reoxygenation speed, G2 and G3 elicit comparable resting hemodynamic responses measured by NIRS. Thus, this study highlights the practicality and effectiveness of using relative occlusion pressures based on systolic blood pressure (SBP) rather than relying on excessively high absolute pressures.

The Discrepancy Between External and Internal Load/Intensity during Blood Flow Restriction Exercise: Understanding Blood Flow Restriction Pressure as Modulating Factor

Physical exercise induces acute psychophysiological responses leading to chronic adaptations when the exercise stimulus is applied repeatedly, at sufficient time periods, and with appropriate magnitude. To maximize long-term training adaptations, it is crucial to control and manipulate the external load and the resulting psychophysiological strain. Therefore, scientists have developed a theoretical framework that distinguishes between the physical work performed during exercise (i.e., external load/intensity) and indicators of the body's psychophysiological response (i.e., internal load/intensity). However, the application of blood flow restriction (BFR) during exercise with low external loads/intensities (e.g., ≤ 30% of the one-repetition-maximum, ≤ 50% of maximum oxygen uptake) can induce physiological and perceptual responses, which are commonly associated with high external loads/intensities. This current opinion aimed to emphasize the mismatch between external and internal load/intensity when BFR is applied during exercise. In this regard, there is evidence that BFR can be used to manipulate both external load/intensity (by reducing total work when exercise is performed to exhaustion) and internal load/intensity (by leading to higher physiological and perceptual responses compared to exercise performed with the same external load/intensity without BFR). Furthermore, it is proposed to consider BFR as an additional exercise determinant, given that the amount of BFR pressure can determine not only the internal but also external load/intensity. Finally, terminological recommendations for the use of the proposed terms in the scientific context and for practitioners are given, which should be considered when designing, reporting, discussing, and presenting BFR studies, exercise, and/or training programs.

Various modalities of resistance exercise promote similar acute cognitive improvements and hemodynamic increases in young, healthy adults

The aim was to examine the effects of modalities of acute resistance exercise (RE) on cognition and hemodynamics including internal carotid artery (ICA) blood flow (BF). Twenty adults completed familiarization and experimental visits. One-repetition maximum (1RM) for bilateral leg extension was quantified, and baseline executive functioning was determined from three run-in visits. Subsequent visits included three randomized, volume-equated, acute exercise bouts of 30 %1RM+blood flow restriction (BFR), 30 %1RM, and 70 %1RM. Both 30 %1RM trials completed four sets of exercise (1 × 30, 3 × 15), and the 70 %1RM condition completed four sets of 8 repetitions. BFR was induced with 40 % of the pressure to occlude the femoral arteries. 11 min following each exercise, participants completed the Stroop and Shifting Attention Tests. Baseline and post-exercise values were used to calculate change scores. The resulting mean change scores were evaluated with mixed factorial ANOVAs. A p≤0.05 was considered significant. All measured outcome variables increased in response to exercise. The ANOVAs for cognitive scores indicated no significant (p>0.05) interactions. For cognitive flexibility and executive function index, there were main effects of Sex. Change scores of the females were significantly greater than the males for cognitive flexibility (7.6 ± 5.9 vs. -2.6 ± 8.4 au; p=0.007) and executive function index (7.4 ± 4.6 vs. -2.5 ± 6.5 au; p=0.001). For ICA BF, there was no significant interaction or any main effect. The females exhibited a smaller exercise-induced increase in blood pressure compared to the males (17.7 ± 5.9 vs. 11.0 ± 4.1 mmHg; p=0.010). Each RE modality yielded acute improvements in cognition, but only for females. There were no cognitive improvements related to BFR such that each RE bout yielded similar results.

Innovations in the Assessment of Skeletal Muscle Health: A Glimpse into the Future

Skeletal muscle is the largest organ system in the human body and plays critical roles in athletic performance, mobility, and disease pathogenesis. Despite growing recognition of its importance by major health organizations, significant knowledge gaps remain regarding skeletal muscle health and its crosstalk with nearly every physiological system. Relevant public health challenges like pain, injury, obesity, and sarcopenia underscore the need to accurately assess skeletal muscle health and function. Feasible, non-invasive techniques that reliably evaluate metrics including muscle pain, dynamic structure, contractility, circulatory function, body composition, and emerging biomarkers are imperative to unraveling the complexities of skeletal muscle. Our concise review highlights innovative or overlooked approaches for comprehensively assessing skeletal muscle in vivo. We summarize recent advances in leveraging dynamic ultrasound imaging, muscle echogenicity, tensiomyography, blood flow restriction protocols, molecular techniques, body composition, and pain assessments to gain novel insight into muscle physiology from cellular to whole-body perspectives. Continued development of precise, non-invasive tools to investigate skeletal muscle are critical in informing impactful discoveries in exercise and rehabilitation science.

Sex-specific microvascular and hemodynamic responses to passive limb heating in young adults

OBJECTIVE

We examined sex-specific microvascular reactivity and hemodynamic responses under conditions of augmented resting blood flow induced by passive heating compared to normal blood flow.

METHODS

Thirty-eight adults (19 females) completed a vascular occlusion test (VOT) on two occasions preceded by rest with or without passive heating in a randomized, counterbalanced order. Skeletal muscle tissue oxygenation (StO2, %) was assessed with near-infrared spectroscopy (NIRS), and the rate of desaturation and resaturation as well as maximal StO2 (StO2max) and prolonged hypersaturation (area under the curve, StO2AUC) were quantified. Before the VOT, brachial artery blood flow (BABF), vascular conductance, and relative BABF (BABF normalized to forearm lean mass) were determined. Sex × condition ANOVAs were used. A p-value ≤.05 was considered statistically significant.

RESULTS

Twenty minutes of heating increased BABF compared to the control (102.9 ± 28.3 vs. 36.0 ± 20.9 mL min-1; p < .01). Males demonstrated greater BABF than females (91.9 ± 34.0 vs. 47.0 ± 19.1 mL min-1; p < .01). There was no sex difference in normalized BABF. There were no significant interactions for NIRS-VOT outcomes, but heat did increase the rate of desaturation (-0.140 ± 0.02 vs. -0.119 ± 0.03% s-1; p < .01), whereas regardless of condition, males exhibited greater rates of resaturation and StO2max than females.

CONCLUSIONS

These results suggest that blood flow is not the primary factor causing sex differences in NIRS-VOT outcomes.

Myofascial release induces declines in heart rate and changes to microvascular reactivity in young healthy adults

OBJECTIVES

The purpose of this study was to compare physiological responses to myofascial release (MFR) and passive limb movement (PLM).

DESIGN

Nineteen (23 ± 2.6yrs) adults (10 men and 9 women) completed two experiments on separate days: MFR and PLM. Participation included collecting ultrasound images, blood pressure, and heart rate (HR) as well as performing a vascular occlusion test (VOT). The VOT assessed muscle tissue oxygenation (StO2) with near-infrared spectroscopy. Experiments consisted of moving the upper limb to release subtle barriers of resistance in the muscle/fascia (MFR) and passive, assisted range of motion (PLM).

RESULTS

There was a significantly (p = 0.012) greater decrease in HR following MFR (-7.3 ± 5.2 BPM) than PLM (-1.3 ± 0.9 BPM). There was an equivalent change in brachial blood flow (-17.3 ± 23.0 vs. -11.9 ± 14.9 mL min-1; p = 0.37) and vascular conductance (-19.3 ± 31.1 vs. -12.4 ± 15.3 mL min-1 mmHg-1; p = 0.38). Microvascular responses differed between the experiments such that MFR exhibited greater area under the curve (AUC, 1503 ± 499.1%∙s-1 vs. 1203 ± 411.1%∙s-1; p = 0.021) and time to maximum StO2 (40.0 ± 8.4s vs. 35.8 ± 7.3s; p = 0.009).

CONCLUSIONS

As evidenced by HR, MFR induced greater parasympathetic activity than PLM. The greater AUC and time to StO2max following MFR suggested a spillover effect to induce prolonged hyper-saturation. These results may be of interest to those investigating possible MFR-related rehabilitative benefits.

Effects of blood flow restriction on spine postural control using a robotic platform: A pilot randomized cross-over study

BACKGROUND

Blood flow restriction (BFR) training improves muscle strength and functional outcomes, but the proprioceptive implications of this technique in the rehabilitation field are still unknown.

OBJECTIVE

The present study aimed at assessing the effects of BFR in terms of stabilometric and balance performance.

METHODS

In this pilot randomized cross-over study, healthy young adults were included and randomly assigned to Groups A and B. Both groups underwent a postural assessment with and without wearing a BFR device. Study participants of Group A underwent postural baseline assessment wearing BFR and then removed BFR for further evaluations, whereas subjects in Group B performed the baseline assessment without BFR and then with BFR. Stabilometric and balance performance were assessed by the robotic platform Hunova, the Balance Error Scoring System (BESS), the self-reported perceived balance (7-point Likert scale), and discomfort self-rated assessment. Moreover, the safety profile was recorded.

RESULTS

Fourteen subjects were included and randomly assigned to Group A (n: 7) and Group B (n: 7). Significant differences were shown in balance tests in static conditions performed on the Hunova robot platform in terms of average distance RMS (root-mean-square) with open eyes (OE), anteroposterior (AP) trunk oscillation range with OE, mediolateral (ML) average speed of oscillation with OE, and total excursion AP range with closed eyes (CE) (BFR: 3.44 ± 1.06; without BFR: 2.75 ± 0.72; p= 0.041). Moreover, elastic balance test showed differences in Romberg index (BFR: 0.16 ±0.16; without BFR: 0.09 ± 0.07; p= 0.047). No adverse events were reported.

CONCLUSION

Taken together, our data showed that BFR affects balance performance of healthy subjects. Further studies are needed to better characterize the possible role of BFR treatment in the context of a specific rehabilitation protocol.