The contribution of muscle hypertrophy to strength changes following resistance training

Purpose

Whilst skeletal muscle hypertrophy is considered an important adaptation to resistance training (RT), it has not previously been found to explain the inter-individual changes in strength after RT. This study investigated the contribution of hypertrophy to individual gains in isometric, isoinertial and explosive strength after 12 weeks of elbow flexor RT.

Methods

Thirty-three previously untrained, healthy men (18–30 years) completed an initial 3-week period of elbow flexor RT (to facilitate neurological responses) followed by 6-week no training, and then 12-week elbow flexor RT. Unilateral elbow flexor muscle strength [isometric maximum voluntary force (iMVF), single repetition maximum (1-RM) and explosive force], muscle volume (V _m), muscle fascicle pennation angle (θ _p) and normalized agonist, antagonist and stabilizer sEMG were assessed pre and post 12-week RT.

Results

Percentage gains in V _m correlated with percentage changes in iMVF (r = 0.527; P = 0.002) and 1-RM (r = 0.482; P = 0.005) but not in explosive force (r ≤ 0.243; P ≥ 0.175). Percentage changes in iMVF, 1-RM, and explosive force did not correlate with percentage changes in agonist, antagonist or stabilizer sEMG (all P > 0.05). Percentage gains in θ _p inversely correlated with percentage changes in normalized explosive force at 150 ms after force onset (r = 0.362; P = 0.038).

Conclusions

We have shown for the first time that muscle hypertrophy explains a significant proportion of the inter-individual variability in isometric and isoinertial strength gains following 12-week elbow flexor RT in healthy young men.     

Muscle strength, volume and activation following 12-month resistance training in 70-year-old males

In elderly males muscle plantar flexor maximal voluntary contraction (MVC) torque normalised to muscle volume (MVC/VOL) is reduced compared to young males as a result of incomplete muscle activation in the elderly. The aim of the present study was to determine the influence of a 12-month resistance training programme on muscle volume, strength, MVC/VOL, agonist activation and antagonist coactivation of the plantarfexors in elderly males. Thirteen elderly males aged 70 years and over (range 70–82 years), completed a 12-month whole body resistance-training programme (TRN), training three times a week. Another eight males (range 18–30 years), who maintained their habitual physical activity for the same 12-month period as the TRN group acted as controls (CTRL). Isometric plantarflexor maximal voluntary contraction (MVC) torque increased in the TRN group by 20% (P<0.01), from 113.1±22.0 Nm to 141.5±19.2 Nm. Triceps surae volume (TS VOL) assessed using MRI, increased by 12%, from 796.3±78.9 cm³ to 916.8±144.4 cm³ . PF activation, measured using supramaximal double twitch interpolation, increased from 83.6±11.0% pre training, to 92.1±7.6% post training (P<0.05). Dorsiflexion MVC and antagonist coactivation (assessed using surface electromyography) did not change with training. Plantarflexor MVC torque normalized for triceps surae muscle volume (MVC/VOL) was 142.6±32.4 kN m^–2 before training and 157.0± 27.9 kN m^–2 after training (a non-significant increase of 8%). No significant change in any measurement was observed in the CTRL group. This study has shown that the gain in muscle strength in response to long-term (12-month) training in older men is mostly accounted for by an increased muscle volume and activation.     

Changes in muscle and joint elasticity following long-term strength training in old age

The current investigation was designed (1) to examine the effect of a 48-week strength training on musculotendinous (MT) and musculoarticular (MA) stiffness characteristics in older men and women; and (2) to evaluate the influence of gender on stiffness behaviour in response to such training. The training was performed twice per week and mainly consisted of three series of 10 repetitions of calf-rise at 75% of the 3-repetition maximum. Two methods were used to perform stiffness measurements during plantar flexion: (1) the use of quick-release movements, allowing the calculation of MT stiffness; (2) the application of sinusoidal perturbations to the joint, allowing the calculation of MA stiffness. In each case, stiffness was linearly related to torque, leading to the calculation of a normalized stiffness index (SI) as the slope of this stiffness-torque relationship: SI_MT and SI_MA, respectively. Results showed a similar decrease in SI_MT among older men (−27%, P < 0.05) and women (−29%, P < 0.05) following training. A decrease in SI_MA was only observed among women (−11%, P < 0.05). The results suggest that (1) MT stiffness decreases following training in older individuals, counterbalancing the effect of ageing; and (2) older men and women respond differently to the same resistance-training stimulus in terms of MA stiffness. Gender-related differences in MA stiffness response may originate from passive MA elastic structures. This work was part of the Better Ageing Program and was supported by grants from the European Commission (Framework Program V, QLRT-2001-00323).     

Effects of detraining following short term resistance training on eccentric and concentric muscle strength

Healthy males were examined before and after 12 weeks of accommodated resistance training (three week^-1) and after 12 weeks of detraining. Training consisted of four to five sets of six coupled maximum voluntary bilateral concentric and eccentric (Grp ECCON; n= 10) or 12 concentric (Grp CON; n= 8) quadriceps muscle actions. Concentric and eccentric peak torque at various constant angular velocities and three repetition maximum half-squat and vertical jump height were measured. Grp ECCON showed greater (P < 0.05) overall increase in peak torque after training and detraining than Grp CON. Thus, concentric peak torque (0.52 rad s^-1) increased more (P < 0.05) over the experimental period in Grp ECCON and increases in eccentric peak torque were preserved in Grp ECCON only. Increases in peak torque in response to training were greater (P < 0.05) at 0.52 than at 2.62 rad s^-1. Alterations in the torque-velocity patterns induced by training remained after detraining in Grp ECCON but not in Grp CON. The retained increases (P < 0.05) in half-squat were 12 and 18% in Grps CON and ECCON, respectively. Neither group showed increased vertical jump height after detraining. This study showed greater preservation of concentric and eccentric peak torque after detraining following coupled concentric and eccentric than concentric resistance training. Only the former regime induced a change in the shape of torque-velocity curves that was manifest after detraining. These results suggest that the performance of eccentric muscle actions is critical to optimize increases in muscular strength in response to heavy resistance training, because it probably induce greater and more long-lived neural adaptations than the performance of concentric actions.     

Increased inspiratory and expiratory muscle strength following respiratory muscle strength training (RMST) in two patients with late-onset Pompe disease

Respiratory muscle strength training (RMST) is an exercise-based intervention which targets respiratory muscle weakness. We implemented RMST in two patients with late-onset Pompe disease (LOPD), both who had received long-term enzyme replacement therapy and had severe respiratory weakness. Over 16–32 weeks, inspiratory muscle strength increased by 73–74%. Expiratory muscle strength increased 31–48% over 12–22 weeks. These findings suggest that RMST may increase respiratory muscle strength, even in the setting of LOPD and severe baseline weakness.     

Effects of detraining following short term resistance training on eccentric and concentric muscle strength.

Healthy males were examined before and after 12 weeks of accommodated resistance training (three week-1) and after 12 weeks of detraining. Training consisted of four to five sets of six coupled maximum voluntary bilateral concentric and eccentric (Grp ECCON; n = 10) or 12 concentric (Grp CON; n = 8) quadriceps muscle actions. Concentric and eccentric peak torque at various constant angular velocities and three repetition maximum half-squat and vertical jump height were measured. Grp ECCON showed greater (P less than 0.05) overall increase in peak torque after training and detraining than Grp CON. Thus, concentric peak torque (0.52 rad s-1) increased more (P less than 0.05) over the experimental period in Grp ECCON and increases in eccentric peak torque were preserved in Grp ECCON only. Increases in peak torque in response to training were greater (P less than 0.05) at 0.52 than at 2.62 rad s-1. Alterations in the torque-velocity patterns induced by training remained after detraining in Grp ECCON but not in Grp CON. The retained increases (P less than 0.05) in half-squat were 12 and 18% in Grps CON and ECCON, respectively. Neither group showed increased vertical jump height after detraining. This study showed greater preservation of concentric and eccentric peak torque after detraining following coupled concentric and eccentric than concentric resistance training. Only the former regime induced a change in the shape of torque-velocity curves that was manifest after detraining.(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscle hypertrophy,hormonal adaptations and strength development during strength training in strength-trained and untrained men

Hormonal and neuromuscular adaptations to strength training were studied in eight male strength athletes (SA) and eight non-strength athletes (NA). The experimental design comprised a 21-week strength-training period. Basal hormonal concentrations of serum total testosterone (T), free testosterone (FT) and cortisol (C) and maximal isometric strength, right leg 1 repetition maximum (RM) of the leg extensors were measured at weeks 0, 7, 14 and 21. Muscle cross-sectional area (CSA) of the quadriceps femoris was measured by magnetic resonance imaging (MRI) at weeks 0 and 21. In addition, the acute heavy resistance exercises (AHRE) (bilateral leg extension, five sets of ten RM, with a 2-min rest between sets) including blood samples for the determination of serum T, FT, C, and GH concentrations were assessed before and after the 21-week training. Significant increases of 20.9% in maximal force and of 5.6% in muscle CSA in NA during the 21-week strength training period were greater than those of 3.9% and −1.8% in SA, respectively. There were no significant changes in serum basal hormone concentrations during the 21-week experiment. AHRE led to significant acute decreases in isometric force and acute increases in serum hormones both at weeks 0 and 21. Basal T concentrations (mean of 0, 7, 14 and 21 weeks) and changes in isometric force after the 21-week period correlated with each other (r=0.84, P<0.01) in SA. The individual changes in the acute T responses between weeks 0 and 21 and the changes in muscle CSA during the 21-week training correlated with each other (r=0.76, P<0.05) in NA. The correlations between T and the changes in isometric strength and in muscle CSA suggest that both serum basal testosterone concentrations and training-induced changes in acute testosterone responses may be important factors for strength development and muscle hypertrophy.     

肌肉力量神经调控与停止训练的关系

背景：当运动员遇到疾病、受伤、旅行等情况时往往会停止训练,这对机体骨骼肌的神经调控的可能产生影响。 目的：全面了解停止训练对机体肌肉力量神经调控能力的影响及其机制。 方法：检索Medline数据库1983/2006收录的停止训练与肌肉力量神经调控的相关综述和论文报告,并根据检索到的文献中所列出的相关参考文献进行追溯查找。 结果与结论：共纳入停止训练与肌肉力量神经调控的相关文献48篇。发现一定持续时间的停止训练可引起最大随意收缩力下降,但可能受到骨骼肌本身、脊髓及脊髓以上中枢的影响;同时,由于运动训练模式、肌肉收缩形式、测试部位、停止训练的状况等不同,可能会使最大随意收缩力及相关神经学适应在停止训练期间被不同程度地保留下来。     

Time course for strength and muscle thickness changes following upper and lower body resistance training in men and women

 The purpose of this study was to investigate the time course of skeletal muscle adaptations resulting from high-intensity, upper and lower body dynamic resistance training (WT). A group of 17 men and 20 women were recruited for WT, and 6 men and 7 women served as a control group. The WT group performed six dynamic resistance exercises to fatigue using 8–12 repetition maximum (RM). The subjects trained 3 days a week for 12 weeks. One-RM knee extension (KE) and chest press (CP) exercises were measured at baseline and at weeks 2, 4, 6, 8, and 12 for the WT group. Muscle thickness (MTH) was measured by ultrasound at eight anatomical sites. One-RM CP and KE strength had increased significantly at week 4 for the female WT group. For the men in the WT group, 1 RM had increased significantly at week 2 for KE and at week 6 for CP. The mean relative increases in KE and CP strength were 19% and 19% for the men and 19% and 27% for the women, respectively, after 12 weeks of WT. Resistance training elicited a significant increase in MTH of the chest and triceps muscles at week 6 in both sexes. There were non-significant trends for increases in quadriceps MTH for the WT groups. The relative increases in upper and lower body MTH were 12%–21% and 7%–9% in the men and 10%–31% and 7%–8% in the women respectively, after 12 weeks of WT. These results would suggest that increases in MTH in the upper body are greater and occur earlier compared to the lower extremity, during the first 12 weeks of a total body WT programme. The time-course and proportions of the increase in strength and MTH were similar for both the men and the women. Accepted: 6 September 1999     

The effects of eccentric and concentric training at different velocities on muscle hypertrophy

The purpose of this study was to examine the effect of isokinetic eccentric (ECC) and concentric (CON) training at two velocities [fast, 180° s⁻¹ (3.14 rad s⁻¹) and slow,30° s⁻¹(0.52 rad s⁻¹)] on muscle hypertrophy. Twenty-four untrained volunteers (age 18–36 years) participated in fast- (n=13) or slow- (n=11) velocity training, where they trained one arm eccentrically for 8 weeks followed by CON training of the opposite arm for 8 weeks. Ten subjects served as controls (CNT). Subjects were tested before and after training for elbow flexor muscle thickness by sonography and isokinetic strength (Biodex). Overall, ECC training resulted in greater hypertrophy than CON training (P<0.01). No significant strength or hypertrophy changes occurred in the CNT group. ECC (180° s⁻¹) training resulted in greater hypertrophy than CON (180° s⁻¹) training and CON (30° s⁻¹) training (P<0.01). ECC (30° s⁻¹) training resulted in greater hypertrophy than CON (180° s⁻¹) training (P<0.05), but not CON (30° s⁻¹) training. ECC (180° s⁻¹) training resulted in the greatest increases in strength (P<0.01). We conclude that ECC fast training is the most effective for muscle hypertrophy and strength gain.     

Specificity of resistance training responses in neck muscle size and strength

This study examined hypertrophy after head extension resistance training to assess which muscles of the complicated cervical neuromuscular system were used in this activity. We also determined if conventional resistance exercises, which are likely to evoke isometric action of the neck, induce generalized hypertrophy of the cervical muscle. Twenty-two active college students were studied. [mean (SE) age, weight and height: 21 (1) years, 71 (4) kg and 173 (3) cm, respectively]. Subjects were assigned to one of three groups: RESX (head extension exercise and other resistance exercises), RES (resistance exercises without specific neck exercise), or CON (no training). Groups RESX (n?=?8) and RES (n?=?6) trained 3 days/week for 12 weeks with large-muscle mass exercises (squat, deadlift, push press, bent row and mid-thigh pull). Group RESX also performed three sets of ten repetitions of a head extension exercise 3 days/week with a load equal to the 3?×?10 repetition maximum (RM). Group CON (n?=?8) was a control group. The cross-sectional area (CSA) of nine individual muscles or muscle groups was determined by magnetic resonance imaging (MRI) of the cervical region. The CSA data were averaged over four contiguous transaxial slices in which all muscles of interest were visible. The 3?×?10 RM for the head extension exercise increased for RESX after training [from 17.9 (1.0) to 23.9 (1.4) kg, P?2, P?2 and 17.0 (2.5) to 17.0 (2.4) cm², respectively]. This hypertrophy for RESX was due mainly to increases in CSA of 23.9 (3.2), 24.0 (5.8), and 24.9 (5.3)% for the splenius capitis, and semispinalis capitis and cervicis muscles, respectively. The lack of?generalized neck muscle hypertrophy in RES was not due to insufficient training. For example, the CSA of their quadriceps femoris muscle group, as assessed by MRI, increased by 7 (1)% after this short-term training (P?相似文献   

肌肉电刺激力量训练影响运动者肌力的Meta分析

文题释义：肌肉电刺激技术(electrical stimulation training,EMS)：是一种通过不同频率脉冲电流刺激机体神经肌肉引起肌肉收缩,从而改善肌肉力量和功能或是治疗神经肌肉系统损伤疾病的物理治疗技术。离心收缩：肌肉在收缩产生张力的同时被拉长的收缩称为离心收缩。肌肉在阻力下逐渐被拉长,使运动环节向肌肉拉力相反的方向运动的收缩方式。是动力性收缩的一种,又称作退让性收缩,其产生的最大肌肉力量比向心收缩要大。背景：研究显示,肌肉电刺激法对于肌肉蛋白的合成和肌肉质量的增长具有一定的改善作用,但也有不同的研究结果。目的：通过Meta分析肌肉电刺激作为力量训练手段对运动人群肌力的影响,旨在为以后运动领域力量训练提供新的方法思路和循证依据。方法：检索PubMed、EBSCO host、Web of Science、CNKI、万方、维普VIP等数据库,收集肌肉电刺激对运动人群肌肉力量的随机对照试验(RCT)。通过PICOS原则筛选纳入文献,试验对象为运动员及有运动经验的健康人群,分为肌肉电刺激组和对照组(不进行任何干预)。运用stata 15.1、reviewmanager 5.3依据cochrane标准进行文章质量评价和结局指标的Meta分析、敏感性分析、亚组分析以及发表偏倚评价。结果与结论：①与对照组相比,肌肉电刺激对运动人群向心收缩峰力矩的提高有显著性作用(合并效应值WMD=8.23,95%CI：6.71-9.76),P < 0.0001),在20岁<年龄≤22岁的年龄段内肌肉电刺激训练对向心收缩峰力矩的影响最有效果;②与对照组相比,肌肉电刺激对运动人群离心收缩峰力矩的提高有显著性作用(合并效应值WMD=5.58,95%CI：4.16-7.00,P < 0.000 01);③对等长收缩峰力矩影响的纳入实验数量较少,不宜进行Meta分析;④结果说明,电刺激训练可有效促进运动人群的向心收缩峰力矩和离心收缩峰力矩,且肌肉电刺激作为训练手段对运动人群肌力训练的作用需要分指标、分年龄、分对象地进行讨论。ORCID: 0000-0002-6616-9437(侯筱)中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Effects of strength and endurance training on isometric muscle strength and walking speed in elderly women

The separate effects of 18 weeks of intensive strength and endurance training on isometric knee extension (KE) and flexion (KF) strength and walking speed were studied in 76-to 78-year-old women. Maximal voluntary isometric force for both KE and KF was measured in a sitting position on a custom-made dynamometer chair at a knee angle of 60° from full extension. Maximal walking speed was measured over a distance of 10 m. The endurance-trained women increased KE torque and KE torque/body mass after the first 9 weeks of training when compared with the controls. When comparing the baseline, 9 week and 18 week measurements within the groups separately, both the endurance- and strength-training groups increased KE torque, KE torque/body mass and walking speed. Individual changes in KE torque/body mass before and after 18 weeks of training averaged 19.1% in the strength group, 30.9% in the endurance group and 2.0% in the controls. This study indicates that in elderly women the effects of physical training on muscle strength and walking speed occur after endurance as well as strength training. The considerable interindividual variation in change of muscle performance is also worth noticing.     

Effects of training and creatine supplement on muscle strength and body mass

The purpose of this study was to test the effect of creatine supplement on the size of the extra- and intra-cellular compartments and on the increase of isokinetic force during a strength training-program. Twenty-five healthy male subjects (age 22.0?±?2.9 years) participated in this experiment. Seven subjects formed the control-group. They did not complete any training and did not have any dietary supplement. The eighteen other subjects were randomly divided into a creatine- (n?=?8) and a placebo-group (n?=?10). They were submitted to a controlled strength-training program for 42 days followed by a detraining period of 21 days. Creatine and placebo were given over a period of 9 weeks. The size of the body water compartments was assessed by bio- impedance spectroscopy and the isokinetic force was determined during a single squat by means of an isokinetic dynamometer. These measurements were completed beforehand, at the end of the training period, and after the determining period. Both placebo- and creatine-group increased the isokinetic force by about 6% after the training period, showing that creatine ingestion does not induce a higher increase of the force measured during a single movement. No change in body mass was observed in the control- and placebo-groups during the entire experiment period while the body mass of the creatine-group was increased by 2?kg (P?P?=?0.039) in the body water content (+1.11), and more specifically, to an increase (P?相似文献   

Shoulder muscle strength in paraplegics before and after kayak ergometer training

The purpose was to investigate if shoulder muscle strength in post-rehabilitated persons with spinal cord injury (SCI) was affected by kayak ergometer training and to compare shoulder strength in persons with SCI and able-bodied persons. Ten persons with SCI (7 males and 3 females, injury levels T3–T12) performed 60 min kayak ergometer training three times a week for 10 weeks with progressively increased intensity. Maximal voluntary concentric contractions were performed during six shoulder movements: flexion and extension (range of motion 65°), abduction and adduction (65°), and external and internal rotation (60°), with an angular velocity of 30° s⁻¹. Position specific strength was assessed at three shoulder angles (at the beginning, middle and end of the range of motion) in the respective movements. Test–retests were performed for all measurements before the training and the mean intraclass correlation coefficient was 0.941 (95% CI 0.928–0.954). There was a main effect of kayak ergometer training with increased shoulder muscle strength after training in persons with SCI. The improvements were independent of shoulder movement, and occurred in the beginning and middle positions. A tendency towards lower shoulder muscle strength was observed in the SCI group compared to a matched reference group of able-bodied persons. Thus, it appears that post-rehabilitated persons with SCI have not managed to fully regain/maintain their shoulder muscle strength on a similar level as that of able-bodied persons, and are able to improve their shoulder muscle strength after a period of kayak ergometer training.     

Alterations of mechanical characteristics of human skeletal muscle during strength training

Summary To investigate the influence of strength training on the mechanical characteristics of human skeletal muscle, 14 male subjects went through training of combined heavy concentric and eccentric contractions three times a week for 16 weeks. The strength training program consisted mainly of dynamic exercises for leg extensors with loads of 80 to 120% of one maximum repetition. The force-time curves produced during various vertical jumps were the basis for calculation of various mechanical parameters. In addition to a great increase (p<0.001) in maximal isometric force, heavy resistance strength training also caused significant (p<0.05–0.01) increases in heights and in various mechanical parameters in positive work phases of vertical and drop jumps. The increase in positive force during a fast dynamic contraction was correlated (p<0.01) with the reduced time to produce a certain submaximal force level in isometric condition. No changes in the elastic properties of the muscle were observed as judged from the difference between the counter-movement and squat jumps. When the training was followed by the 8-week detraining period a great decrease (p<0.001) in maximal force took place, but only minor changes (ns) were observed in fast force production.Supported in part by the grants from The Finnish Olympic Committee and Central Sport Federation     

Combined effects of low-intensity blood flow restriction training and high-intensity resistance training on muscle strength and size

We investigated the combined effect of low-intensity blood flow restriction and high-intensity resistance training on muscle adaptation. Forty young men (aged 22–32 years) were randomly divided into four groups of ten subjects each: high-intensity resistance training (HI-RT, 75% of one repetition maximum [1-RM]), low-intensity resistance training with blood flow restriction (LI-BFR, 30% 1-RM), combined HI-RT and LI-BFR (CB-RT, twice-weekly LI-BFR and once-weekly HI-RT), and nontraining control (CON). Three training groups performed bench press exercises 3 days/week for 6 weeks. During LI-BFR training sessions, subjects wore pressure cuffs on both arms that were inflated to 100–160 mmHg. Increases in 1-RM were similar in the HI-RT (19.9%) and CB-RT (15.3%) groups and lower in the LI-BFR group (8.7%, p < 0.05). Maximal isometric elbow extension (MVC) increased in the HI-RT (11.3%) and CB-RT (6.6%) groups; there was no change in the LI-BFR group (−0.2%). The cross-sectional area (CSA) of the triceps brachii (TB) increased (p < 0.05) in the HI-RT (8.6%), CB-RT (7.2%), and LI-BFR (4.4%) groups. The change in relative isometric strength (MVC divided by TB CSA) was greater (p < 0.05) in the HI-RT group (3.3%) than in the LI-BFR (−3.5%) and CON (−0.1%) groups. Following training, relative dynamic strength (1-RM divided by TB CSA) was increased (p < 0.05) by 10.5% in the HI-RT group and 6.7% in the CB-RT group. None of the variables in the CON group changed. Our results show that low-intensity resistance training with BFR-induced functional muscle adaptations is improved by combining it with HI-RT.