Blood flow restriction: effects of cuff type on fatigue and perceptual responses to resistance exercise.

Blood flow restriction (BFR) combined with low load resistance training has been shown to result in muscle hypertrophy similar to that observed with higher loads. However, not all studies have found BFR efficacious, possibly due to methodological differences. It is presently unclear whether there are differences between cuffs of similar size (5 cm) but different material (nylon vs. elastic). The purpose was to determine if there are differences in repetitions to fatigue and perceptual ratings of exertion (RPE) and discomfort between narrow elastic and narrow nylon cuffs. Sixteen males and females completed three sets of BFR knee extension exercise in a randomized cross-over design using either elastic or nylon restrictive cuffs applied at the proximal thigh. There were no differences in repetitions to fatigue (marker of blood flow) or perceptual ratings between narrow elastic and narrow nylon cuffs. This data suggests that either elastic or nylon cuffs of the same width should cause similar degrees of BFR at the same pressure during resistance exercise.

Relationship between lifting performance and skeletal muscle mass in elite powerlifters.

AIM: Aim of the study was to examine the relationship between whole body skeletal muscle mass (SMM) and powerlifting performance in elite powerlifters. METHODS: Twenty elite male powerlifters, including 4 world champions, volunteered. Muscle thickness (MTH) and subcutaneous fat thickness (FTH) were measured by ultrasound at 9 sites on the anterior and posterior aspects of the body. FTH was used to estimate body fat and fat-free mass and SMM was estimated from ultrasound-derived prediction equations. Best lifting performance in the squat (SQ), bench press (BP), and dead lift (DL) was recorded from competition performance. RESULTS: Significant strong correlations (P<0.01) were observed between absolute and relative (divided by height) SMM and performance of the SQ (r=0.93 and r=0.94, respectively), BP (r=0.88 and r=0.87), and DL (r=0.84 and r=0.85). Relative lifting performance to SMM for squat (SQ/SMM ratio) and bench press (BP/SMM ratio) were constant throughout a wide range of weight classes (56kg-145kg) and there were no significant correlation between the SMM and those performances (r=0.21 for SQ and r=0.12 for BP). However, the DL/SMM ratio was negatively correlated to DL performance (r=-0.47, P<0.05). CONCLUSION: SMM is a good predictor of powerlifting performance throughout all weight classes.

Resting and post exercise arterial-ventricular coupling in endurance-trained men and women.

The relationship between effective arterial elastance (EA) and left ventricular end-systolic elastance (ELV) is a determinant of cardiac performance, known as arterial-ventricular coupling (AVC). The purpose of this study was to examine the acute effects of high-intensity interval (HI) and low-intensity steady state (SS) exercise on AVC. Twenty-three (13 men, 10 women) young (26 years), endurance-trained individuals completed a VO2 peak test followed by an acute SS and HI exercise bout on separate visits. Before (Pre) and 30- and 60-min after each bout, measures of aortic end-systolic pressure (ESP), left ventricular end-systolic volume and stroke volume were obtained. Across both conditions (HI and SS) and both sexes, at 30 and 60 min post exercise, ESP and ELV were reduced from Pre 30 and 60-min exercise (ESP: 86±7, 77±8 and 73±8 mm Hg; ELV: 4.93±1.53, 4.19±1.38 and 4.10±1.53 mm Hg ml(-1) m(-2)). EA was only reduced at 60 min post exercise (1.90±0.36, 1.78±0.50 and 1.57±0.36). Both EA and ELV were reduced following acute SS and HI exercise. This is likely because of similar reductions in total peripheral resistance following both exercise bouts. These results suggest that endurance-trained individuals are able to match peripheral vascular changes with changes in left ventricular function following dynamic exercise of different intensities.

The acute muscle swelling effects of blood flow restriction.

The purpose of this study was to investigate the potential mechanisms behind the blood flow restriction (BFR) stimulus in the absence of exercise. Nine participants completed a 10 minute time control and then a BFR protocol. The protocol was five, 5-minute bouts of inflation with 3-minutes of deflation between each bout. The pressure was set relative to each individual's thigh circumference. Significant increases in muscle thickness were observed for both the vastus lateralis (VL) [6%, p = 0.027] and rectus femoris (RF) [22%, p = 0.001] along with a significant decrease in plasma volume [15%, p = 0.001]. Ratings of discomfort during the BFR protocol peaked at 2.7 (light discomfort). There were no significant changes with whole blood lactate, electromyography (EMG), or heart rate (HR), however, there was a trend for a significant increase in HR during the 5th inflation (p = 0.057). In conclusion, this is the first study to demonstrate that the attenuation of both muscle atrophy and declines in strength previously observed with brief applications of BFR may have been mediated through an acute fluid shift induced increase in muscle size. This is supported by our finding that the changes in muscle thickness are maintained even after the cuffs have been removed.

Blood flow restriction: an evidence based progressive model (Review).

To remain independent and healthy, an important factor to consider is the maintenance of skeletal muscle mass. Inactivity leads to measurable changes in muscle and bone, reduces exercise capacity, impairs the immune system, and decreases the sensitivity to insulin. Therefore, maintaining physical activity is of great importance for skeletal muscle health. One form of structured physical activity is resistance training. Generally speaking, one needs to lift weights at approximately 70% of their one repetition maximum (1RM) to have noticeable increases in muscle size and strength. Although numerous positive effects are observed from heavy resistance training, some at risk populations (e.g. elderly, rehabilitating patients, etc.) might be advised not to perform high-load resistance training and may be limited to performance of low-load resistance exercise. A technique which applies pressure cuffs to the limbs causing blood flow restriction (BFR) has been shown to attenuate atrophy and when combined with low intensity exercise has resulted in an increase in both muscle size and strength across different age groups. We have provided an evidence based model of progression from bed rest to higher load resistance training, based largely on BFR literature concentrating on more at risk populations, to highlight a possible path to recovery.

Aortic reservoir function, estimated myocardial demand and coronary perfusion pressure following steady-state and interval exercise.

Aortic reservoir function is a measure of the aorta's ability to distribute blood during diastole, attenuating the pulsatility of blood flow, and is important in balancing cardiac flow. Effects of acute high versus moderate exercise intensity on reservoir function and cardiac energetics is unknown. Eighteen athletes completed a interval (INT) and steady-state (SS) cycling bout at 60% of VO(2) peak. Reservoir function was calculated as the ratio of diastolic run-off to stroke volume and expressed as a percentage. Coronary perfusion pressure was derived from tissue Doppler imaging and echocardiography. Systolic tension-time integral (TTI) from the aortic pressure waveform served as a measure of myocardial oxygen consumption. All measures were made at rest, 30-min postexercise and 60-min postexercise. Average reservoir function before SS was 76%, which was reduced to 62% 30-min post-SS and 67% 60-min post-SS (P<0.05). Significantly greater reductions in reservoir function were seen following INT (from 71% pre-INT to 45% 30-min post-INT and 53% 60-min INT, P<0.05). Estimated coronary perfusion pressure was reduced 30 min following INT but not SS; both bouts reduced coronary perfusion pressure at 60-min postexercise (P<0.05). TTI increased following both INT and SS at 30- and 60-min postexercise with greater increases following INT (P<0.05). Following exercise, reservoir function was associated with TTI (P<0.05), but not coronary perfusion pressure (P>0.05). We conclude that reservoir function is attenuated following acute SS and INT, but these reductions were greater post-INT, suggesting that exercise intensity affects reservoir function. Reduction of reservoir function following exercise is related to TTI, a reflection of myocardial oxygen consumption but apparently not associated with coronary perfusion pressure.

Comparison of the acute impact of maximal arm and leg aerobic exercise on arterial stiffness.

Acute aerobic exercise decreases arterial stiffness based on the intensity of the exercise and the arterial segment studied. Arm exercise may differentially affect arterial stiffness compared to leg exercise but this has not been studied. We hypothesized that maximal aerobic exercise would reduce local peripheral pulse wave velocity i.e. femoral-dorsalis pedis (LPWV) following leg exercise and carotid-radial (APWV) following arm exercise without any crossover effect. The main purpose of the study is to compare the effects of maximal arm versus leg aerobic exercise on peripheral and central arterial stiffness. Fifteen healthy participants (9 males and 6 females, 25 ± 5 years) performed maximal arm-ergometer and leg-ergometer exercise in a randomized, crossover design. Peripheral and central pulse wave velocities (PWV) were obtained using applanation tonometry before and 10 min after each maximal exercise bout. 2 × 2 repeated measures analysis of variance was used to detect differences between conditions. There was a significant interaction in the APWV between the two exercise modes. However, there was no condition or interaction effect on LPWV following maximal arm versus leg exercise. There was no significant difference in central PWV between conditions or with time. There was no change in MAP (75 ± 6-77 ± 3) after maximal arm exercise as compared to the maximal leg exercise (73 ± 6-80 ± 2). Arm exercise produced a more generalized effect on arterial stiffness than leg exercise. The prescription of upper limb exercise may be considered for purposes of eliciting post-exercise systemic changes in arterial stiffness.

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.

Effects of calcium diet supplements on egg strength in conventional and furnished cages, and effects of 2 different nest floor materials.

Several studies have demonstrated a greater incidence of cracked eggs in furnished than in conventional cages. Hens kept in furnished cages may have greater bone strength, so they may lay eggs with weaker shells because they may utilize more calcium for bone mineralization and less for shell formation. The effects of increased dietary calcium content were therefore studied in 3-hen conventional and 8-hen furnished cages. In addition, the effects of 2 different nest floor materials were studied in furnished cages. A total of 1,216 Lohmann Selected Leghorn hens were housed in either furnished or conventional cages and offered either the normal calcium supplementation used in commercial diets (37 to 40 g of calcium/kg) or increased calcium supplementation (44 to 50 g of calcium/kg) consisting of added limestone for 3 consecutive feeding phases of 20, 16, and 16 wk. Dietary calcium had similar effects in both cage systems. Greater limestone supplementation increased the laying rate (P < 0.05). Increased dietary limestone had no significant effects on egg quality, and no effects on tibia-breaking strength or specific gravity were observed. The laying rate was higher in conventional than in furnished cages (P < 0.05), but there was no significant difference between the cage types in terms of total egg mass produced. The cage type had no effect on tibia-breaking strength. However, the specific gravity and ash content of tibias were higher in hens kept in furnished than in conventional cages (P < 0.001). Based on this study, the weakening of eggshells in furnished cages is not caused by a possible calcium shortage resulting from high bone mineralization.

Effects of dietary energy content on the performance of laying hens in furnished and conventional cages.

This study examined the effects of dietary energy content on the egg production and egg quality of hens kept in 3-hen conventional cages or 8-hen furnished cages. A total of 1,088 Lohmann Selected Leghorn hens were housed in either furnished or conventional cages and offered low- or high-energy diets (from 2,342 to 2,414 kcal/kg or from 2,581 to 2,629 kcal/kg) during 3 consecutive feeding phases of 20, 16, and 16 wk, respectively. The same dietary energy effects were observed in both cage systems. The hens that received the low-energy diet consumed more feed (P < 0.01) and produced fewer eggs per day (P < 0.05) than the birds fed the high-energy diet. Over the entire experiment, housing had no significant effects on production parameters, but during the third feeding phase, the production rate was smaller in furnished cages than in conventional cages (P < 0.01). Because of the greater live weight of the hens in furnished cages at the beginning of the experiment, these hens consumed more feed during the first feeding phase than the hens in conventional cages. During the third feeding phase, the hens in furnished cages consumed less feed than those in conventional cages (P < 0.01), probably because of their better feather cover. No differences in feed conversion ratio were found between the cage types. The results of this study confirm the results of previous studies providing evidence of equal production rates and feed conversion ratios in furnished and conventional cages.

Effect of vitamin D2- and D3-enriched diets on egg vitamin D content, production, and bird condition during an entire production period.

Vitamin D insufficiency during winter is a common problem for humans in Europe. One way to ease this problem is through the production of vitamin D-fortified eggs. To evaluate such a production process, the effects of vitamin D supplementation during an entire production period were assessed. Transfer of vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol) from the diet to egg yolks was measured using 2 different levels of both vitamins (6,000 and 15,000 IU/kg feed) relative to a control treatment (2,500 IU vitamin D3/kg feed). During the experiment, production parameters, egg quality (egg weight, Haugh unit, specific gravity, eggshell fracture force, and Ca content of eggshell), and the condition of hens were monitored. At the end of the experiment histopathological tests were performed. Supplementing diets with vitamin D3 increased egg yolk vitamin D content more effectively than did supplementation with vitamin D2. For groups of hens receiving 6,000 or 15,000 IU of vitamin D3/kg feed, egg yolk vitamin D3 content ranged from 9.1 to 13.6 and from 25.3 to 33.7 microg/100 g, respectively. Corresponding values for birds fed vitamin D2 were 4.7 to 7.0 and 13.3 to 21.0 microg/100 g. Both supplements enhanced vitamin D3 content of egg yolks relative to the control diet (2.5 to 5.0 microg/100 g of egg yolk). Vitamin D supplements had no effects on production parameters compared with the control diet. However, especially vitamin D3 improved bone strength (P < 0.05). Autopsy at the end of the experiment indicated no detrimental accumulation of calcium in the kidneys, liver, heart, muscles, or lungs.

Effects of above-ground browsing by mammals on mycorrhizal infection in an early successional taiga ecosystem.

Using an exclosure experiment in the willow stage of primary succession on the floodplain of the Tanana River, we tested the hypothesis that browsing can reduce mycorrhizal infection. We measured the effects winter browsing by moose (Alcesalces) and snowshoe hare (Lepusamericanus) had on mycorrhizal infection and fine root biomass of willow (Salix spp.) and balsam poplar (Populusbalsamifera). We found that protection from winter browsing increased ectomycorrhizal infection by 10% in the top 5 cm of the soil profile, by 23% at 5-10 cm, and by 42% at the 10-15 cm depth. Mammal browsing in taiga forests is now recognized as a major cause of the shift from palatable deciduous species such as willow and balsam poplar to less palatable species such as alder and spruce. We suggest that browsing-induced reduction in ectomycorrhizal infection of salicaceous species plays a central role in this shift in plant community composition.