The addition of blood flow restriction during resistance exercise does not increase prolonged low-frequency force depression.

At a given exercise intensity, blood flow restriction (BFR) reduces the volume of exercise required to impair post-exercise neuromuscular function. Compared to traditional exercise, the time course of recovery is less clear. After strenuous exercise, force output assessed with electrical muscle stimulation is impaired to a greater extent at low versus high stimulation frequencies, a condition known as prolonged low-frequency force depression (PLFFD). It is unclear if BFR increases PLFFD after exercise. This study tested if BFR during exercise increases PLFFD and slows recovery of neuromuscular function compared to regular exercise. Fifteen physically active participants performed six low-load sets of knee-extensions across four conditions: resistance exercise to task failure (RETF), resistance exercise to task failure with BFR applied continuously (BFRCONT) or intermittently (BFRINT), and resistance exercise matched to the lowest exercise volume condition (REVM). Maximal voluntary contraction (MVC) force output, voluntary activation and a force-frequency (1-100 Hz) curve were measured before and 0, 1, 2, 3, 4 and 24 h after exercise. Exercise to task failure caused similar reductions at 0 h for voluntary activation (RETF = 81.0 ± 14.2%, BFRINT = 80.9 ± 12.4% and BFRCONT = 78.6 ± 10.7%) and MVC force output (RETF = 482 ± 168 N, BFRINT = 432 ± 174 N, and BFRCONT = 443 ± 196 N), which recovered to baseline values between 4 and 24 h. PLFFD occurred only after RETF at 1 h supported by a higher frequency to evoke 50% of the force production at 100 Hz (1 h: 17.5 ± 4.4 vs. baseline: 15 ± 4.1 Hz, P = 0.0023), BFRINT (15.5 ± 4.0 Hz; P = 0.03), and REVM (14.9 ± 3.1 Hz; P = 0.002), with a trend versus BFRCONT (15.7 ± 3.5 Hz; P = 0.063). These findings indicate that, in physically active individuals, using BFR during exercise does not impair the recovery of neuromuscular function by 24 h post-exercise.

A comparison of low volume 'high-intensity-training' and high volume traditional resistance training methods on muscular performance, body composition, and subjective assessments of training.

Most studies of resistance training (RT) examine methods that do not resemble typical training practices of persons participating in RT. Ecologically valid RT programs more representative of such practices are seldom compared. This study compared two such approaches to RT. Thirty participants (males, n = 13; females, n = 17) were randomised to either a group performing low volume 'High Intensity Training' (HIT; n = 16) or high volume 'Body-building' (3ST; n = 14) RT methods 2x/week for 10 weeks. Outcomes included muscular performance, body composition, and participant's subjective assessments. Both HIT and 3ST groups improved muscular performance significantly (as indicated by 95% confidence intervals) with large effect sizes (ES; 0.97 to 1.73 and 0.88 to 1.77 respectively). HIT had significantly greater muscular performance gains for 3 of 9 tested exercises compared with 3ST (p < 0.05) and larger effect sizes for 8 of 9 exercises. Body composition did not significantly change in either group. However, effect sizes for whole body muscle mass changes were slightly more favourable in the HIT group compared with the 3ST group (0.27 and -0.34 respectively) in addition to whole body fat mass (0.03 and 0.43 respectively) and whole body fat percentage (-0.10 and -0.44 respectively). Significant muscular performance gains can be produced using either HIT or 3ST. However, muscular performance gains may be greater when using HIT. Future research should look to identify which components of ecologically valid RT programs are primarily responsible for these differences in outcome.

Blood flow restricted and traditional resistance training performed to fatigue produce equal muscle hypertrophy.

This study investigated the hypertrophic potential of load-matched blood-flow restricted resistance training (BFR) vs free-flow traditional resistance training (low-load TRT) performed to fatigue. Ten healthy young subjects performed unilateral BFR and contralateral low-load TRT elbow flexor dumbbell curl with 40% of one repetition maximum until volitional concentric failure 3 days per week for 6 weeks. Prior to and at 3 (post-3) and 10 (post-10) days post-training, magnetic resonance imaging (MRI) was used to estimate elbow flexor muscle volume and muscle water content accumulation through training. Acute changes in muscle thickness following an early vs a late exercise bout were measured with ultrasound to determine muscle swelling during the immediate 0-48 h post-exercise. Total work was threefold lower for BFR compared with low-load TRT (P < 0.001). Both BRF and low-load TRT increased muscle volume by approximately 12% at post-3 and post-10 (P < 0.01) with no changes in MRI-determined water content. Training increased muscle thickness during the immediate 48 h post-exercise (P < 0.001) and to greater extent with BRF (P < 0.05) in the early training phase. In conclusion, BFR and low-load TRT, when performed to fatigue, produce equal muscle hypertrophy, which may partly rely on transient exercise-induced increases in muscle water content.

Optimal criteria and sampling interval to detect a V̇O2 plateau at V̇O2max in patients with metabolic syndrome.

This study sought to determine the optimal criteria and sampling interval to detect a V̇O2 plateau at V̇O2max in patients with metabolic syndrome. Twenty-three participants with criteria-defined metabolic syndrome underwent a maximal graded exercise test. Four different sampling intervals and three different V̇O2 plateau criteria were analysed to determine the effect of each parameter on the incidence of V̇O2 plateau at V̇O2max. Seventeen tests were classified as maximal based on attainment of at least two out of three criteria. There was a significant (p < 0.05) effect of 15-breath (b) sampling interval on the incidence of V̇O2 plateau at V̇O2max across the ≤ 50 and ≤ 80 mL ∙ min(-1) conditions. Strength of association was established by the Cramer's V statistic (φc); (≤ 50 mL ∙ min(-1) [φc = 0.592, p < 0.05], ≤ 80 mL ∙ min(-1) [φc = 0.383, p < 0.05], ≤ 150 mL ∙ min(-1) [φc = 0.246, p > 0.05]). When conducting maximal stress tests on patients with metabolic syndrome, a 15-b sampling interval and ≤ 50 mL ∙ min(-1) criteria should be implemented to increase the likelihood of detecting V̇O2 plateau at V̇O2max.

A reduced core to skin temperature gradient, not a critical core temperature, affects aerobic capacity in the heat.

The purpose of this study was to determine the impact of the core to skin temperature gradient during incremental running to volitional fatigue across varying environmental conditions. A secondary aim was to determine if a "critical" core temperature would dictate volitional fatigue during running in the heat. 60 participants (n=49 male, n=11 female; 24±5 yrs, 177±11 cm, 75±13 kg) completed the study. Participants were uniformly stratified into a specific exercise temperature group (18 °C, 26 °C, 34 °C, or 42 °C) based on a 3-mile run performance. Participants were equipped with core and chest skin temperature sensors and a heart rate monitor, entered an environmental chamber (18 °C, 26 °C, 34 °C, or 42 °C), and rested in the seated position for 10 min before performing a walk/run to volitional exhaustion. Initial treadmill speed was 3.2 km h(-1) with a 0% grade. Every 3 min, starting with speed, speed and grade increased in an alternating pattern (speed increased by 0.805 km h(-1), grade increased by 0.5%). Time to volitional fatigue was longer for the 18 °C and 26 °C group compared to the 42 °C group, (58.1±9.3 and 62.6±6.5 min vs. 51.3±8.3 min, respectively, p<0.05). At the half-way point and finish, the core to skin gradient for the 18 °C and 26 °C groups was larger compared to 42 °C group (halfway: 2.6±0.7 and 2.0±0.6 vs. 1.3±0.5 for the 18 °C, 26 °C and 42 °C groups, respectively; finish: 3.3±0.7 and 3.5±1.1 vs. 2.1±0.9 for the 26 °C, 34 °C, and 42 °C groups, respectively, p<0.05). Sweat rate was lower in the 18 °C group compared to the 26 °C, 34 °C, and 42 °C groups, 3.6±1.3 vs. 7.2±3.0, 7.1±2.0, and 7.6±1.7 g m(-2) min(-1), respectively, p<0.05. There were no group differences in core temperature and heart rate response during the exercise trials. The current data demonstrate a 13% and 22% longer run time to exhaustion for the 18 °C and 26 °C group, respectively, compared to the 42 °C group despite no differences in beginning and ending core temperatures or baseline 3-mile run time. This capacity difference appears to result from a magnified core to skin gradient via an environmental temperature advantageous to convective heat loss, and in part from an increased sweat rate.

Blood flow restriction does not alter the early hypertrophic signaling and short-term adaptive response to resistance exercise when performed to task failure.

Previous research supports that low-load resistance exercise with blood flow restriction (LL-BFR) acutely increases physiological responses and muscle mass accrual compared with low-load resistance exercise (LL-RE) alone. However, most studies have work-matched LL-BFR and LL-RE. Completing sets to similar perceived efforts, thereby allowing for a variable amount of work, may provide a more ecologically valid approach to compare LL-BFR and LL-RE. This study aimed to examine acute signaling and training responses following LL-RE or LL-BFR performed to task failure. Ten participants had each leg randomly assigned to perform LL-RE or LL-BFR. Muscle biopsies were obtained before and 2-h after the first exercise bout and after 6-wk of training for Western blot and immunohistochemistry analyses. Repeated measure ANOVA and intraclass coefficients (ICCs) were used to compare responses of each condition. After exercise, AKT(T308) phosphorylation increased after LL-RE and LL-BFR (both ∼145% of baseline, P < 0.05) and trended for p70 S6K(T389) (LL-RE: ∼158% and LL-BFR: ∼137%, P = 0.06). BFR did not alter these responses, resulting in fair-excellent ICCs for signaling proteins involved in anabolism (ICCAKT(T308) = 0.889, P = 0.001; ICCAKT(S473) = 0.519, P = 0.074; ICCp70 S6K(T389) = 0.514, P = 0.105). After training, muscle fiber cross-sectional area and vastus lateralis whole muscle thickness were similar between conditions (ICC ≥ 0.637, P ≤ 0.031). Similar acute and chronic responses between conditions and high ICC values between legs suggest that both LL-BFR and LL-RE performed by the same person result in similar adaptations. These data support the concept that sufficient muscular exertion is a key factor for training-induced muscle hypertrophy with low-load resistance exercise independent of total work and blood flow.NEW & NOTEWORTHY The addition of blood flow restriction during low-load resistance exercise is considered to increase the signaling events and muscle growth responses to a greater extent than low-load resistance exercise alone. It remains unclear whether blood flow restriction accelerates or increases these adaptive responses, as most studies have each condition perform the same amount of work. Despite different amounts of work performed, we show similar signaling and muscle growth responses occur after low-load resistance exercise with and without blood flow restriction. Our work supports that blood flow restriction accelerates fatigue but does not increase the signaling events and muscle growth responses during low-load resistance exercise.