Christopher A. Fahs

The anabolic benefits of venous blood flow restriction training may be induced by muscle cell swelling

Venous blood flow restriction (VBFR) combined with low intensity resistance exercise (20-30% concentric 1-RM) has been observed to result in skeletal muscle hypertrophy, increased strength, and increased endurance. Knowledge of the mechanisms behind the benefits seen with VBFR is incomplete, but the benefits have traditionally been thought to occur from the decreased oxygen and accumulation of metabolites. Although many of the proposed mechanisms appear valid and are likely true with VBFR combined with resistance exercise, there are certain situations in which benefits are observed without a large accumulation of metabolites and/or large increases in fast twitch fiber type recruitment. Cell swelling appears to be a likely mechanism that appears to be present throughout all studies. VBFR may be able to induce cell swelling through a combination of blood pooling, accumulation of metabolites, and reactive hyperemia following the removal of VBFR which may contribute to skeletal muscle adaptations that occur with VBFR. We hypothesize that cell swelling is important for muscle growth and strength adaptation but when coupled with higher metabolic accumulation, this adaptation is even greater.

Blood flow restriction: the metabolite/volume threshold theory.

Traditionally it has been thought that muscle hypertrophy occurs primarily from an overload stimulus produced by progressively increasing an external load using at least 70% of ones concentric one repetition maximum (1RM). Blood flow restricted exercise has been demonstrated to result in numerous positive training adaptions, specifically muscle hypertrophy and strength at intensities much lower than this recommendation. The mechanisms behind these adaptions are currently unknown but a commonly cited concept is that acute elevations of systemic hormones, specifically growth hormone (GH), play a large role with resistance training induced muscle hypertrophy, possibly through stimulating muscle protein synthesis (MPS). We hypothesize that the alterations in the intramuscular environment which results in the rapid recruitment of FT fibers, is the large driving force behind the skeletal muscle hypertrophy seen with blood flow restriction, whereas the external load and systemic endogenous hormone elevations may not be as important as once thought. It is further hypothesized that although skeletal muscle hypertrophy can be achieved at low intensities without blood flow restriction when taken to muscular failure, the overall volume of work required is much greater than that needed with blood flow restriction.

Resistance exercise training reduces central blood pressure and improves microvascular function in African American and white men

OBJECTIVE African American men have stiffer large central arteries and impaired dilation of smaller peripheral arteries when compared to their white peers. The purpose of this study was to examine the effect of resistance exercise training (RT) on vascular function and central blood pressure (BP) in young (22 years) African American and white men. METHODS Vascular and hemodynamic measures were made in 19 African American and 18 white men at baseline and following 6-weeks of RT. Carotid BP and carotid/brachial artery beta-stiffness were measured by tonometry and ultrasonography, respectively. Aortic BP was measured by radial artery tonometry and a generalized transfer function. Aortic stiffness was measured by pulse wave velocity (PWV). Forearm blood flow (FBF) was measured by strain-gauge plethysmography before and during reactive hyperemia (RH) induced by 5-min of brachial artery occlusion. RESULTS There were similar reductions in central BP and similar increases in FBF-RH in both African American and white men following RT (p<0.05). There were no changes in brachial systolic BP, carotid stiffness, and aortic PWV in either group (p>0.05). There was an increase in brachial stiffness in African American but not white men following RT (p<0.05). CONCLUSIONS RT led to reductions in central BP and increases in microvascular endothelial function with no effect on central artery stiffness in both groups of young men. RT increased brachial stiffness in African American men. Measurement of conventional brachial BP does not capture the central hemodynamic and vascular response to exercise training due to disparate racial changes in regional vascular properties.

Hemodynamic and Vascular Response to Resistance Exercise with L-Arginine

PURPOSE L-arginine, the precursor to nitric oxide (NO), has been shown to improve endothelial function in patients with endothelial dysfunction. Resistance exercise has been shown to increase arterial stiffness acutely with no definitive cause. It is possible that a reduction in NO bioavailability is responsible for this. The purpose of this study was to examine the effect of acute L-arginine supplementation and resistance exercise on arterial function. METHODS Eighteen (N = 18) young men (24.2 +/- 0.7 yr) volunteered for this study. In a crossover design, subjects underwent body composition testing, 1-repetition maximum testing for the bench press and the biceps curls and performed two acute bouts of resistance exercise in which they consumed either placebo or 7 g L-arginine before each resistance exercise bout. Anthropometric measures, augmentation index (AIx), arterial stiffness, and forearm blood flow (FBF) were assessed before and after each treatment condition. RESULTS There were significant (P < 0.05) time effects after the resistance exercise; there was a reduction in brachial stiffness (P = 0.0001), an increase in central aortic stiffness (P = 0.004), an increase in AIx (P = 0.023), an increase in FBF (P = 0.000), and an increase in arm circumference (P = 0.0001) after exercise. CONCLUSIONS The increase in central arterial stiffness and wave reflection was not attenuated by acute supplementation with L-arginine; furthermore, blood flow was not augmented with supplementation. On the basis of these data, l-arginine does not appear to change the hemodynamic and vascular responses to resistance exercise.

Impact of Excess Body Weight on Arterial Structure, Function, and Blood Pressure in Firefighters

Cardiovascular disease is the leading cause of death among firefighters. The purpose of the present study was to examine the effect of excess body weight on arterial structure and function and blood pressure (BP) in relatively young, apparently healthy, firefighters. The body mass index, brachial BP, carotid BP, aortic BP, radial augmentation index, central pulse wave velocity, forearm blood flow, forearm vasodilatory capacity, carotid arterial compliance, carotid intima-media thickness, and brachial flow-mediated dilation were assessed in 110 firefighters (aged 29.7 +/- 8.0 years). The group was divided into equal tertiles according to the body mass index (<25.9, 25.9 to 29.4, and >or=29.5 kg/m(2)). Group differences in hemodynamics, anthropometrics, microvascular function, and macrovascular structure and function were tested using multivariate analysis of variance. The obese group was older, heavier, and had a larger waist circumference compared to the lean and overweight groups (p <0.05). The overweight group was also older, heavier, and had a larger waist circumference than the lean group (p <0.05). Compared to the lean group, the overweight and obese groups had a greater systolic BP (p <0.05). The obese group also had a significantly greater mean arterial BP and carotid systolic BP than the lean group (p <0.05). The obese group had greater beta stiffness and elastic modulus compared to the lean and overweight groups (p <0.05), but no group differences were found in endothelial function. In conclusion, in a population of relatively young firefighters, an increased body mass index was associated with elevated peripheral BP and arterial stiffness, with no apparent decrements in endothelial function.

Exercise intensity and muscle hypertrophy in blood flow–restricted limbs and non‐restricted muscles: a brief review

Although evidence for high‐intensity resistance training–induced muscle hypertrophy has accumulated over the last several decades, the basic concept of the training can be traced back to ancient Greece: Milo of Croton lifted a bull‐calf daily until it was fully grown, which would be known today as progressive overload. Now, in the 21st century, different types of training are being tested and studied, such as low‐intensity exercise combined with arterial as well as venous blood flow restriction (BFR) to/from the working muscles. Because BFR training requires the use of a cuff that is placed at the proximal ends of the arms and/or legs, the BFR is only applicable to limb muscles. Consequently, most previous BFR training studies have focused on the physiological adaptations of BFR limb muscles. Muscle adaptations in non‐BFR muscles of the hip and trunk are lesser known. Recent studies that have reported both limb and trunk muscle adaptations following BFR exercise training suggest that low‐intensity (20–30% of 1RM) resistance training combined with BFR elicits muscle hypertrophy in both BFR limb and non‐BFR muscles. However, the combination of leg muscle BFR with walk training elicits muscle hypertrophy only in the BFR leg muscles. In contrast to resistance exercise with BFR, the exercise intensity may be too low during BFR walk training to cause muscle hypertrophy in the non‐BFR gluteus maximus and other trunk muscles. Other mechanisms including hypoxia, local and systemic growth factors and muscle cell swelling may also potentially affect the hypertrophic response of non‐BFR muscles to BFR resistance exercise.

Physiological recovery from firefighting activities in rehabilitation and beyond.

Abstract Objectives. The primary objective of this study was to document the timeline of physiologic recovery from firefighting activities in order to inform emergency medical services (EMS) of vital sign values that might be expected during incident rehabilitation and in developing rehabilitation protocols to make decisions about when to return personnel to the fireground. Secondarily, we compared two different incident rehabilitation strategies to determine effectiveness in reducing physiologic strain following firefighting. Methods. A repeated-measures randomized crossover design was utilized in which firefighters conducted a controlled set of firefighting activities, after which they completed incident rehabilitation in one of two conditions: 1) similar to currently used rehabilitation protocols and 2) with active cooling and nutritional intervention. Following 15 minutes of rehabilitation, each firefighter was asked to perform a simulated rescue “dummy drag” and then recover for 120 minutes in a quiet area. Core temperature and heart rate were recorded throughout the study. Blood pressures and subendocardial viability ratios were obtained before firefighting, after firefighting, and at standardized times during rehabilitation and recovery. Results. Heart rate and core temperature increased during firefighting, and core temperature continued to increase for 7 minutes after completion of firefighting activities. These values did not return to baseline until at least 50 minutes after firefighting activity. Systolic blood pressures were significantly reduced during rehabilitation (15.2%), and recovered 7.7% during the first 30 minutes of recovery, but remained significantly lower than before firefighting for at least 120 minutes. An index of subendocardial perfusion was also significantly depressed for up to 110 minutes after firefighters. Differences between rehabilitation protocols were minimal. Conclusions. The timeline for recovery from firefighting activities is significantly longer than the typical 10–20-minute rehabilitation period that often is provided on the fireground. Modifications from the current rehabilitation protocol do not appear to improve the recovery timeline when rehabilitation is conducted in a cool room. While firefighters often are concerned about elevated blood pressures, this study suggests that firefighters and EMS personnel should also be cognizant of the potential dangers of hypotension.

Cardiovascular and perceptual responses to blood‐flow‐restricted resistance exercise with differing restrictive cuffs

The purpose of this study was to determine (i) the cardiovascular responses to acute blood‐flow‐restricted (BFR) resistance exercise and (ii) the influence of applied BFR cuff type on the cardiovascular and perceptual responses.

The effect of acute fish-oil supplementation on endothelial function and arterial stiffness following a high-fat meal

This study examined whether a commercially available fish-oil supplement offers protection from the acute effects of a high-fat meal (HFM) on endothelial function and arterial stiffness. An HFM causes acute impairments in endothelial function, whereas the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have a variety of cardioprotective effects. However, little is known about the efficacy of moderate fish-oil supplementation on the endothelial dysfunction induced by an HFM. Endothelial function (brachial artery flow-mediated dilation (FMD)), forearm blood flow (FBF), total hyperemia, central and peripheral blood pressure, and central artery stiffness were assessed in 20 healthy men (n = 10) and women (n = 10) at rest and 4 h after an HFM supplemented with either placebo or approximately 1 g EPA and DHA. Brachial artery FMD normalized for shear rate was significantly impaired (p = 0.033) following the HFM with placebo but remained unchanged compared with baseline following the HFM with the fish-oil supplement (p = 0.039; condition x time interaction). Resting FBF (p = 0.020) and total hyperemia (p = 0.014) were elevated following the HFM. All other vascular and hemodynamic measurements were unchanged in both trials. Commercially available fish-oil supplements taken with an HFM appear to preserve endothelial function following an HFM.

Muscular strength is inversely associated with aortic stiffness in young men.

UNLABELLED Muscular strength is associated with reduced mortality. Paradoxically, strength training may increase central artery stiffness, a predictor of cardiovascular morbidity and mortality. However, the relationship between muscular strength and central arterial stiffness has yet to be defined. PURPOSE The purpose of this study was to determine the relationship between muscular strength and central arterial stiffness in young men. METHODS Central and peripheral pulse wave velocity (PWV), augmentation index, muscular strength, and aerobic capacity (V O2peak) were measured in 79 young men (mean +/- SD, age = 23 +/- 4 yr). Height, weight, and brachial blood pressure were also recorded. Muscular strength was determined using a one-repetition maximum bench press and normalized to bodyweight. Spearman correlations were used to determine the relationships between relative strength, aerobic fitness, and hemodynamic/vascular measures. RESULTS There was a significant negative correlation between central PWV and strength (r = -0.222, P < 0.05). The relationship remained significant when controlling for aerobic fitness (r = -0.189, P < 0.05). Muscular strength was significantly higher (P < 0.05) in men with low central PWV (5.2 +/- 0.4 m.s) compared with men with high central PWV (6.6 +/- 0.4 m.s). CONCLUSION These results show that there is a significant inverse association between muscular strength and aortic stiffness independent of aerobic fitness.