Article

Muscle-specific neuromuscular responses during running with blood flow restriction

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Abstract

The purpose of this investigation was to examine muscle excitation at maximal running capacity without blood flow restriction (BFR) relative to submaximal running bouts with BFR. Fourteen college-aged males randomly completed four, three-minute running bouts at 70, 80, and 90% of peak speed with BFR (70%BFR, 80%BFR, and 90%BFR) and without BFR at 100% of their peak speed (100%NOBFR). The surface electromyographic amplitudes of the vastus lateralis, rectus femoris, and vastus medialis muscles were assessed. Muscle excitation of the vastus lateralis was similar across most bouts; however, it was lower during the 70%BFR compared to 90%BFR (Meandiff =−4.67±− 0.22%; Bayesian 95% high-density interval [HDI]: − 7.07 to − 2.2) and 100%NOBFR (Meandiff =−2.94±− 0.27%; 95% HDI:−5.33 to−0.50) bouts. For the rectus femoris, muscle excitation largely increased across running speeds (70%BFR<80%BFR < 90%BFR; 90%BFR < 100%NOBFR). For the vastus medialis, muscle excitation was lower during the 70%BFR compared to 90%BFR (Meandiff =−8.15±− 0.28%; 95% HDI:−15.3 to−0.89). Submaximal running with BFR increased muscle excitation responses for the vastus lateralis and vastus medialis, such that muscle excitation was similar to 100%BFR, despite 10–20% reductions in running speed. The rectus femoris muscle, however, was not affected by BFR during the submaximal running bouts.

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The main objective of this article is to investigate the empirical performances of the Bayesian approach in analyzing structural equation models with small sample sizes. The traditional maximum likelihood (ML) is also included for comparison. In the context of a confirmatory factor analysis model and a structural equation model, simulation studies are conducted with the different magnitudes of parameters and sample sizes n = da, where d = 2, 3, 4 and 5, and a is the number of unknown parameters. The performances are evaluated in terms of the goodness-of-fit statistics, and various measures on the accuracy of the estimates. The conclusion is: for data that are normally distributed, the Bayesian approach can be used with small sample sizes, whilst ML cannot.
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This study examined the relationships among the physical working capacity at the fatigue threshold (PWCFT), the power outputs associated with the gas exchange threshold (PGET) and the respiratory compensation point (PRCP), and critical power (CP) to identify possible physiological mechanisms underlying the onset of neuromuscular fatigue. Ten participants (mean ± SD age: 20 ± 1 years) performed a maximal incremental cycle ergometer test to determine the PWCFT, PGET, and PRCP. CP was determined from the 3 min all-out test. The PWCFT (197 ± 55 W), PRCP (212 ± 50 W), and CP (208 ± 63 W) were significantly greater than the PGET (168 ± 40 W), but there were no significant differences among the PWCFT, PRCP, and CP. All thresholds were significantly inter-4 (r = 0.794-0.958). The 17% greater estimates for the PWCFT than PGET were likely related to differences in the physiological mechanisms that underlie these fatigue thresholds, while the non-significant difference and high correlation between the PWCFT and the PRCP suggested that hyperkalemia may underlie both thresholds. Furthermore, it is possible that the 5% lower estimate of the PWCFT than CP could more accurately reflect the demarcation of the heavy from severe exercise intensity domains.
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Introduction: We examined the individual patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF) during incremental treadmill running. Methods: Nine physically active men performed incremental treadmill running at a constant grade of 1%. The EMG signal was recorded from the 3 superficial quadriceps femoris muscles during the work bout. Results: The results of the polynomial regression indicated that the linear model best fit the data for the composite data for all 3 muscles and the majority (7 of 9) of subjects. There were no consistent patterns of responses for the EMG MPF responses. Also, there were no significant (P > 0.05) muscle × running velocity interactions for EMG amplitude and MPF. Conclusions: These results indicate consistent patterns of responses for EMG amplitude during incremental treadmill running, regardless of which muscle was studied.
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Vascular blood flow restriction (vBFR) training stimulates muscle hypertrophy by increasing muscle activation and muscle swelling. Previous studies used expensive pneumatic cuffs, which may not be practical for regular use. PURPOSE:: To investigate the acute effects of low intensity practical BFR (LI-pBFR) on muscle activation, muscle swelling and damage. METHODS:: Twelve trained male participants completed a 30, 15, 15, 15 repetition scheme at 30% of their leg press 1-RM under control and LI-BFR conditions. Under the LI-BFR trial, knee wraps were applied to the thighs at a pressure which resulted in venous, not arterial, occlusion. In the control trial, wraps were applied with zero pressure. Ultrasound determined muscle thickness was recorded at baseline, 0 minutes post with wraps, 0, 5 and 10 minutes post without wraps. Muscle activation was recorded during warm ups and on the final set of 15 repetitions. Indices of muscle damage (soreness, power, and muscle swelling) were also recorded. RESULTS:: There was a condition by time effect for muscle thickness (p < 0.0001, ES = 0.5), in which muscle thickness increased in the LI-pBFR condition 0 minutes post with wraps and through 5 minutes post without wraps. No changes occurred in the control. There was a condition by time effect for muscle activation (p < .05, ES = 0.2). LI-pBFR had greater activation than the control. There were no condition by time effects on indices of muscle damage. DISCUSSION:: Our data indicates that practical BFR significantly increases muscle activation and muscle thickness without increasing indices of damage.
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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.
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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 one's 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.
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Presently available tests of physical working capacity (PWC) such as [Vdot]O2max and critical power may not be appropriate for unfit subjects because they require maximal or supramaximal workloads. Therefore, the purpose of this study was to evaluate a submaximal discontinuous incremental bicycle ergometer test (PWCFT) with an end point (fatigue threshold) determined by recording electromyographic (EMG) fatigue curves in the quadriceps muscle. The fatigue threshold was defined as the lowest workload producing a slope of the EMG voltage-time relation that was significantly different from zero slope at p
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The knowledge of surface electromyography (SEMG) and the number of applications have increased considerably during the past ten years. However, most methodological developments have taken place locally, resulting in different methodologies among the different groups of users.A specific objective of the European concerted action SENIAM (surface EMG for a non-invasive assessment of muscles) was, besides creating more collaboration among the various European groups, to develop recommendations on sensors, sensor placement, signal processing and modeling. This paper will present the process and the results of the development of the recommendations for the SEMG sensors and sensor placement procedures. Execution of the SENIAM sensor tasks, in the period 1996-1999, has been handled in a number of partly parallel and partly sequential activities. A literature scan was carried out on the use of sensors and sensor placement procedures in European laboratories. In total, 144 peer-reviewed papers were scanned on the applied SEMG sensor properties and sensor placement procedures. This showed a large variability of methodology as well as a rather insufficient description. A special workshop provided an overview on the scientific and clinical knowledge of the effects of sensor properties and sensor placement procedures on the SEMG characteristics. Based on the inventory, the results of the topical workshop and generally accepted state-of-the-art knowledge, a first proposal for sensors and sensor placement procedures was defined. Besides containing a general procedure and recommendations for sensor placement, this was worked out in detail for 27 different muscles. This proposal was evaluated in several European laboratories with respect to technical and practical aspects and also sent to all members of the SENIAM club (>100 members) together with a questionnaire to obtain their comments. Based on this evaluation the final recommendations of SENIAM were made and published (SENIAM 8: European recommendations for surface electromyography, 1999), both as a booklet and as a CD-ROM. In this way a common body of knowledge has been created on SEMG sensors and sensor placement properties as well as practical guidelines for the proper use of SEMG.
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Low-intensity (approximately 50% of a single repetition maximum-1 RM) resistance training combined with vascular occlusion results in increases in muscle strength and cross-sectional area [Takarada et al. (2002) Eur J Appl Physiol 86:308-331]. The mechanisms responsible for this hypertrophy and strength gain remain elusive and no study has assessed the contribution of neuromuscular adaptations to these strength gains. We examined the effect of low-intensity training (8 weeks of unilateral elbow flexion at 50% 1 RM) both with (OCC) and without vascular occlusion (CON) on neuromuscular changes in the elbow flexors of eight previously untrained men [19.5 (0.4) years]. Following training, maximal voluntary dynamic strength increased (P<0.05) in OCC (22%) and CON (23%); however, isometric maximal voluntary contraction (MVC) strength increased in OCC only (8.3%, P<0.05). Motor unit activation, assessed by interpolated twitch, was high (approximately 98%) in OCC and CON both pre- and post-training. Evoked resting twitch torque decreased 21% in OCC (P<0.05) but was not altered in CON. Training resulted in a reduction in the twitch:MVC ratio in OCC only (29%, P<0.01). Post-activation potentiation (PAP) significantly increased by 51% in OCC (P<0.05) and was not changed in CON. We conclude that low-intensity resistance training in combination with vascular occlusion produces an adequate stimulus for increasing muscle strength and causes changes in indices of neuromuscular function, such as depressed resting twitch torque and enhanced PAP.
Declaration of Helsinki: Ethical principles for medical research involving human subjects
World Medical Association. Declaration of Helsinki: Ethical principles for medical research involving human subjects. JAMA 2013; 310: 2191-2194