Mathias Wernbom

The Influence of Frequency, Intensity, Volume and Mode of Strength Training on Whole Muscle Cross-Sectional Area in Humans

Strength training is an important component in sports training and rehabilitation. Quantification of the dose-response relationships between training variables and the outcome is fundamental for the proper prescription of resistance training. The purpose of this comprehensive review was to identify dose-response relationships for the development of muscle hypertrophy by calculating the magnitudes and rates of increases in muscle cross-sectional area induced by varying levels of frequency, intensity and volume, as well as by different modes of strength training.Computer searches in the databases MEDLINE, SportDiscus® and CJNAHL® were performed as well as hand searches of relevant journals, books and reference lists. The analysis was limited to the quadriceps femoris and the elbow flexors, since these were the only muscle groups that allowed for evaluations of dose-response trends. The modes of strength training were classified as dynamic external resistance (including free weights and weight machines), accommodating resistance (e.g. isokinetic and semi-isokinetic devices) and isometric resistance. The subcategories related to the types of muscle actions used. The results demonstrate that given sufficient frequency, intensity and volume of work, all three types of muscle actions can induce significant hypertrophy at an impressive rate and that, at present, there is insufficient evidence for the superiority of any mode and/or type of muscle action over other modes and types of training. Tentative dose-response relationships for each variable are outlined, based on the available evidence, and interactions between variables are discussed. In addition, recommendations for training and suggestions for further research are given.

Ischemic strength training: a low-load alternative to heavy resistance exercise?

Strength training with low loads in combination with vascular occlusion has been proposed as an alternative to heavy resistance exercise in the rehabilitation setting, especially when high forces acting upon the musculo‐skeletal system are contraindicated. Several studies on low‐to‐moderate intensity resistance exercise combined with cuff occlusion have demonstrated increases in muscle strength and size that are comparable to those typically seen after conventional high‐load strength training. However, the physiological mechanisms by which occlusion training induces increased muscle mass and strength are currently unclear, although several candidate stimuli have been proposed. Also, the long‐term safety, practicality, and efficacy of this training method are still controversial. Furthermore, recent studies have demonstrated that in some instances, tourniquet cuffs may not be necessary for relative ischemia and significant training effects to occur with resistance exercise at low‐to‐moderate loads. The aims of the present review are to summarize current opinion and knowledge regarding the physiology of ischemic strength training and to discuss some of the training and health aspects of this type of exercise. In addition, suggestions for further research are given.

Acute effects of blood flow restriction on muscle activity and endurance during fatiguing dynamic knee extensions at low load.

Wernbom, M, Järrebring, R, Andreasson, MA, and Augustsson, J. Acute effects of blood flow restriction on muscle activity and endurance during fatiguing dynamic knee extensions at low load. J Strength Cond Res 23(8): 2389-2395, 2009-The purpose of this study was to investigate muscle activity and endurance during fatiguing low-intensity dynamic knee extension exercise with and without blood flow restriction. Eleven healthy subjects with strength training experience performed 3 sets of unilateral knee extensions with no relaxation between repetitions to concentric torque failure at 30% of the 1 repetition maximum. One leg was randomized to exercise with cuff occlusion and the other leg to exercise without occlusion. The muscle activity in the quadriceps was recorded with electromyography (EMG). Ratings of perceived exertion (RPE) and acute pain were collected immediately, and delayed onset muscle soreness (DOMS) was rated before and at 24, 48, and 72 hours after exercise. The results demonstrated high EMG levels in both experimental conditions, but there were no significant differences regarding maximal muscle activity, except for a higher EMG in the eccentric phase in set 3 for the nonoccluded condition (p = 0.005). Significantly more repetitions were performed with the nonoccluded leg in every set (p < 0.05). The RPE and acute pain ratings were similar, but DOMS was higher in the nonoccluded leg (p < 0.05). We conclude that blood flow restriction during low-intensity dynamic knee extension decreases the endurance but does not increase the maximum muscle activity compared with training without restriction when both regimes are performed to failure. The high levels of muscle activity suggest that performing low-load dynamic knee extensions in a no-relaxation manner may be a useful method in knee rehabilitation settings when large forces are contraindicated. However, similarly to fatiguing blood flow restricted exercise, this method is associated with ischemic muscle pain, and thus its applications may be limited to highly motivated individuals.

Effects of Vascular Occlusion on Muscular Endurance in Dynamic Knee Extension Exercise at Different Submaximal Loads

Strength training with low load under conditions of vascular occlusion has been proposed as an alternative to heavy-resistance exercise in the rehabilitation setting, when large forces acting upon the musculoskeletal system are unwanted. Little is known, however, about the relative intensity at which occlusion of blood flow significantly reduces dynamic muscular endurance and, hence, when it may increase the training effect. The purpose of this study was to investigate endurance during dynamic knee extension at different loads with and without cuff occlusion. Sixteen subjects (20–45 years of age) with strength-training experience were recruited. At 4 test sessions, the subjects performed unilateral knee extensions to failure with and without a pressure cuff around the thigh at 20, 30, 40, and 50% of their 1 repetition maximum (1RM). The pressure cuff was inflated to 200 mm Hg during exercise with occlusion. Significant differences in the number of repetitions performed were found between occluded and nonoccluded conditions for loads of 20, 30, and 40% of 1RM (p < 0.01) but not for the 50% load (p = 0.465). Thus, the application of a pressure cuff around the thigh appears to reduce dynamic knee extension endurance more at a low load than at a moderate load. These results may have implications regarding when it could be useful to apply a tourniquet in order to increase the rate of fatigue and perhaps also the resulting training effect. However, the short- and long-term safety of training under ischemic conditions needs to be addressed in both healthy and less healthy populations. Furthermore, the high acute pain ratings and the delayed-onset muscle soreness associated with this type of training may limit its potential use to highly motivated individuals.

Acute response and subcellular movement of HSP27, αB-crystallin and HSP70 in human skeletal muscle after blood-flow-restricted low-load resistance exercise.

Heat‐shock proteins (HSP) are important chaperones for stressed and damaged proteins. Low‐load blood‐flow‐restricted resistance exercise (BFRE) is generally believed not to induce significant muscle damage, but is hitherto unverified with intracellular markers. Consequently, the aim of this study was to investigate the HSP response after BFRE in human skeletal muscle.

Blood flow-restricted strength training displays high functional and biological efficacy in women: a within-subject comparison with high-load strength training

Limited data exist on the efficacy of low-load blood flow-restricted strength training (BFR), as compared directly to heavy-load strength training (HST). Here, we show that 12 wk of twice-a-week unilateral BFR [30% of one repetition maximum (1RM) to exhaustion] and HST (6-10RM) of knee extensors provide similar increases in 1RM knee extension and cross-sectional area of distal parts of musculus quadriceps femoris in nine untrained women (age 22 ± 1 yr). The two protocols resulted in similar acute increases in serum levels of human growth hormone. On the cellular level, 12 wk of BFR and HST resulted in similar shifts in muscle fiber composition in musculus vastus lateralis, evident as increased MyHC2A proportions and decreased MyHC2X proportions. They also resulted in similar changes of the expression of 29 genes involved in skeletal muscle function, measured both in a rested state following 12 wk of training and subsequent to singular training sessions. Training had no effect on myonuclei proportions. Of particular interest, 1) gross adaptations to BFR and HST were greater in individuals with higher proportions of type 2 fibers, 2) both BFR and HST resulted in approximately four-fold increases in the expression of the novel exercise-responsive gene Syndecan-4, and 3) BFR provided lesser hypertrophy than HST in the proximal half of musculus quadriceps femoris and also in CSApeak, potentially being a consequence of pressure from the tourniquet utilized to achieve blood flow restriction. In conclusion, BFR and HST of knee extensors resulted in similar adaptations in functional, physiological, and cell biological parameters in untrained women.

Sarcolemmal permeability and muscle damage as hypertrophic stimuli in blood flow restricted resistance exercise (Reply to Loenneke and Abe)

Dear Editor,We welcome the letter by Loenneke and Abe (2011)relating to our recent publication (Wernbom et al. 2011), aswe feel that the topics are of importance and deserve fur-ther discussion.1. Regarding their first point, we were interested instudying the recovery of maximal voluntary contraction(MVC) during maintained partial blood flow restriction(BFR) in order to document the acute effects of our BFRmodel on muscle function during and after exercise, whileblood flow was still restricted. We were also aiming tostudy later recovery, hence our choice of time points.2. Regarding their second point, we acknowledge thatthere were no significant differences in MVC after the BFRwas released. However, there was a trend for MVC of theBFR leg to still be reduced at 72 h post-exercise(p\0.10), the nonsignificance possibly reflecting a type IIerror. Nevertheless, some signs of membrane permeabilitywere present also in the free-flow leg, see below.Concerning signs of damage in the BFR leg, Umbelet al. (2009) demonstrated greater reductions in MVC(-14.1 vs. -1.5%) in the BFR leg than in the free-flowtrained leg at 24 h post-exercise. Interestingly, inspectionof their figures on vastus lateralis cross-sectional area(CSA) reveals a muscle swelling of *5.5% at 24 h post-exercise (vs. *2% in the free-flow leg), and the swelling at24 h was significant when the CSA data for both legs werecombined. The moderate torque decrements, muscleswelling and delayed onset muscle soreness (DOMS) areconsistent with the suggestion of mild muscle damage, asproposed by Umbel et al. (2009). The torque decrements,the signs of increased membrane permeability, the pro-longed increase in resting tension, and DOMS in our study(Wernbom et al. 2011) are also consistent with thisproposal.There are other reports that signs of muscle damage canbe induced by low-to-moderate load resistance exerciseduring ischemic conditions (see point 3), and also a casereport on rhabdomyolysis after BFR-resistance exercise(Iversen and Rostad 2010). These findings suggest that thepotential for muscle damage with strenuous acute BFR-resistance exercise needs to be taken seriously.However, it should also be emphasised that this was thefirst time that our subjects performed strenuous BFR-resistance exercise. It is our experience that the symptomsof muscle damage are much less evident with subsequentbouts, suggesting a protective ‘‘repeated-bout effect’’similar to that for eccentric exercise.3. Concerning Loenneke and Abe’s third point, it shouldbe noted that the exercise was performed without relaxa-tion between repetitions. Signs of ischemia with continuousdynamic knee-extensions have been noted at loads as lowas 10% of MVC (Shoemaker et al. 1994), and isometricknee-extensions at 25–35% of MVC elicited a similar