Skeletal muscle contractility is preserved in COPD patients with normal fat‐free mass

Aim: Peripheral muscle dysfunction often occurs in patients with chronic obstructive pulmonary disease (COPD). The muscle dysfunction may be caused by a loss of force‐generating capacity, resulting from a loss of muscle mass, as well as by other alterations in contractile properties of skeletal muscle. Methods: The maximal isometric voluntary strength and fatigability were determined in hand‐grip and quadriceps muscles from nine male COPD patients (FEV₁ 30–50% predicted) and control subjects matched for fat‐free mass (FFM), physical activity level and age. Contractile properties and fatigability of the quadriceps muscle were also studied with electrically evoked isometric contractions. Results: The maximal voluntary force (MVC) and fatigability of the handgrip muscle did not differ between the COPD patients and control subjects. Also the MVC of the quadriceps muscle and the rate of force rise, contraction time, force–frequency relationship and fatigability, as determined with electrically evoked contractions, were similar in patients with COPD and control subjects. Conclusion: Skeletal muscle strength, contractile properties and fatigability are preserved in patients with moderate COPD and a normal FFM and activity level. This suggests that skeletal muscle dysfunction does not take place during moderate COPD until cachexia and/or a decline in physical activity occur.     

EMG power spectra of cervical muscles in lateral flexion and comparison with sagittal and oblique plane activities

The purpose of this study was to calculate electromyographic (EMG) power spectra of the sternocleidomastoid (SCM), the splenius capitis (SPL) and the trapezius (TRP) muscles from both sides of the body in bilateral lateral flexion and compare them with the EMG spectral characteristics of the same muscles in the sagittal and oblique planes recorded from the same subjects in the same experimental session but reported elsewhere in the literature. Forty normal and healthy young adults (21 males, 19 females) volunteered for the study. The subjects were prepared and positioned appropriately to exert linearly ramping isometric exertion aided by visual feedback against a rigid and load cell instrumental device. Exertions were carried out in a random order. The maximal voluntary contraction was reached within a 5-s test period. The torque and EMG from the SCM, SPL and TRP muscles were sampled bilaterally at a rate of 1 kHz. The EMG data were subjected to fast Fourier transform analysis. During lateral flexion, the torque generated by females was significantly lower than males (P<0.01) and represented at 75% of male torque. Contrary to flexion/extension and oblique plane activities, the ipsilateral SCM was most active with highest power and up to four dominant frequencies demonstrating four distinct peaks. The bandwidth of this muscle progressively increased with the grade of contraction up to 400 Hz, similar to flexion/extension with median frequency (MF) spread between 21 and 109 Hz for males and 78 and 99 Hz for females. The ipsilateral SPL was the second most active muscle, which maintained a narrow bandwidth (200 Hz) and one dominant frequency, rising in power with increasing grade of contraction. Flexion and extension caused symmetrical activity bilaterally. The results of MANOVA revealed a significant main effect of gender, activity direction, grade of contraction and individual muscles (P<0.001). There was a significant interaction between muscle and activity direction (P<0.001) implying significantly different MF and mean power frequency if the direction of exertion was changed. Male and female subjects responded to direction differently (P<0.001). Electronic Publication     

Effects of isometric strength training on quadriceps muscle properties in over 55 year olds

Changes in strength, speed and size of the quadriceps muscle have been investigated in elderly men and women after 6 months of isometric strength training. We have also indirectly investigated the role of metabolites as a stimulus for muscle hypertrophy by studying two training protocols. One thigh was trained using short, intermittent contractions (IC), while the other trained using long, continuous contractions (CC). This meant that there should be a greater metabolite change in the muscle performing CC, as the blood flow is occluded for longer. Nine subjects [eight women, mean (SE) age, 71.8 (2.9) years] were measured for contractile properties and strength before and after training, and compared to nine age-matched controls [71.5 (2.1) years]. The training group increased quadriceps strength by 48.7 (9.1)% (P < 0.005) and 53.1 (11.3) % (P < 0.005) following the IC and CC protocols, respectively. There was no change in muscle strength in the controls. Both muscles showed significant slowing after training as measured by the relaxation times and the force-frequency ratio. There were non-significant decreases in muscle fatigability after training. The control group also showed some significant decreases in fatigability and muscle speed. The training group showed significant increases in muscle (and bone) cross-sectional area of 4.0 (1.7)% and 4.9 (1.3)% following the CC and IC protocols, respectively. These increases were significantly different from the decrease observed in the control group. These findings suggest that people over the age of 55 still have the capacity to increase muscle strength and size, and that the training causes slowing of the muscle. Muscle hypertrophy does not seem to be strongly influenced by metabolite changes in this age group, as there were no differences in measurements observed between protocols.     

Tissue motion pattern of ventral neck muscles investigated by tissue velocity ultrasonography imaging

We designed this experimental study to investigate tissue motions and thus infer the recruitment pattern of the ventral neck muscles [sternocleidomastoid (SCM), longus capitis (Lca), and longus colli (Lco)] at the C4–C5 level in healthy volunteers during isometric manual resistance of the head in flexion in a seated position. This exercise is used in the physiotherapeutic treatment of neck pain and is assumed to activate the deep ventral muscles, but the assumption has not been clearly evaluated. Neck flexors of 16 healthy volunteers (mean age 24 years, SD 3.7) were measured using ultrasonography with strain and strain rate (SR) tissue velocity imaging (TVI) during isometric contraction of flexor muscles. TVI involves using Doppler imaging to study tissue dynamics. All three muscles showed a deformation compared to rest. Except for the initial contraction phase, Lco exhibited a lower strain than Lca and SCM but was the only muscle with a significant change in SR between the phases. When the beginning of the contraction phase was analysed, Lco was the first to be deformed among most volunteers, followed by Lca and then SCM. The exercise investigated seems to be useful as a “stabilizing” exercise for Lco. Our suggestion is that in further research, Lco and Lca should be investigated as separate muscles. TVI could be used to study tissue motions and thus serve as an indicator of muscle patterning between the neck flexors, with the possibility of separating Lco and Lca.     

Response of the trunk muscles to training assessed by magnetic resonance imaging and muscle strength

Summary A group of 12 sedentary medical students (1 man and 11 women aged 21–27 years) participated in a strength training programme for the trunk muscles lasting 18 weeks. The maximal isometric flexion and extension forces of the trunk muscles were measured before the training and at 18 weeks by dynamometer. The cross-sectional area of the back muscles, i.e. erector spinae, multifidus and psoas muscles, was measured from magnetic resonance images (spin echo sequence TR/TE 1500/80, slice thickness 10 mm) obtained at the L4–L5 disc level before the training, at 11 and 18 weeks. During training, no significant change in the body mass or body fat content was found. Muscle forces or muscle cross-sectional area were not related to body mass. There was a significant increase in both trunk muscle cross-sectional area (psoas muscle P<0.001 and back muscles P<0.01) and trunk muscle forces (flexion and extension forces P<0.01) during the training but no direct association between the muscle cross-sectional area and strength of the flexors and extensors was detected before or after the training.     

Skeletal muscle contractility is preserved in COPD patients with normal fat-free mass

AIM: Peripheral muscle dysfunction often occurs in patients with chronic obstructive pulmonary disease (COPD). The muscle dysfunction may be caused by a loss of force-generating capacity, resulting from a loss of muscle mass, as well as by other alterations in contractile properties of skeletal muscle. METHODS: The maximal isometric voluntary strength and fatigability were determined in hand-grip and quadriceps muscles from nine male COPD patients (FEV(1) 30-50% predicted) and control subjects matched for fat-free mass (FFM), physical activity level and age. Contractile properties and fatigability of the quadriceps muscle were also studied with electrically evoked isometric contractions. RESULTS: The maximal voluntary force (MVC) and fatigability of the handgrip muscle did not differ between the COPD patients and control subjects. Also the MVC of the quadriceps muscle and the rate of force rise, contraction time, force-frequency relationship and fatigability, as determined with electrically evoked contractions, were similar in patients with COPD and control subjects. CONCLUSION: Skeletal muscle strength, contractile properties and fatigability are preserved in patients with moderate COPD and a normal FFM and activity level. This suggests that skeletal muscle dysfunction does not take place during moderate COPD until cachexia and/or a decline in physical activity occur.     

Neural control of superficial and deep neck muscles in humans

Human neck muscles have a complex multi-layered architecture. The role and neural control of these neck muscles were examined in nine seated subjects performing three series of isometric neck muscle contractions: 50-N contractions in eight fixed horizontal directions, 25-N contractions, and 50-N contractions, both with a continuously changing horizontal force direction. Activity in the left sternocleidomastoid, trapezius, levator scapulae, splenius capitis, semispinalis capitis, semispinalis cervicis, and multifidus muscles was measured with wire electrodes inserted at the C(4)/C(5) level under ultrasound guidance. We hypothesized that deep and superficial neck muscles would function as postural and focal muscles, respectively, and would thus be controlled by different neural signals. To test these hypotheses, electromyographic (EMG) tuning curves and correlations in the temporal and frequency domains were computed. Three main results emerged from these analyses: EMG tuning curves from all muscles exhibited well-defined preferred directions of activation for the 50-N isometric forces, larger contractions (25 vs. 50 N) yielded more focused EMG tuning curves, and agonist neck muscles from all layers received a common neural drive in the range of 10-15 Hz. The current results demonstrate that all neck muscles can exhibit phasic activity during isometric neck muscle contractions. Similar oscillations in the EMG of neck muscles from different layers further suggest that neck motoneurons were activated by common neurons. The reticular formation appears a likely generator of the common drive to the neck motoneurons due to its widespread projections to different groups of neck motoneurons.     

Strength increases from the motor program: comparison of training with maximal voluntary and imagined muscle contractions.

1. This study addressed potential neural mechanisms of the strength increase that occur before muscle hypertrophy. In particular we examined whether such strength increases may result from training-induced changes in voluntary motor programs. We compared the maximal voluntary force production after a training program of repetitive maximal isometric muscle contractions with force output after a training program that did not involve repetitive activation of muscle; that is, after mental training. 2. Subjects trained their left hypothenar muscles for 4 wk, five sessions per week. One group produced repeated maximal isometric contractions of the abductor muscles of the fifth digit's metacarpophalangeal joint. A second group imagined producing these same, effortful isometric contractions. A third group did not train their fifth digit. Maximal abduction force, flexion/extension force and electrically evoked twitch force (abduction) of the fifth digit were measured along with maximal integrated electromyograms (EMG) of the hypothenar muscles from both hands before and after training. 3. Average abduction force of the left fifth digit increased 22% for the Imagining group and 30% for the Contraction group. The mean increase for the Control group was 3.7%. 4. The maximal abduction force of the right (untrained) fifth digit increased significantly in both the Imagining and Contraction groups after training (10 and 14%, respectively), but not in the Control group (2.3%). These results are consistent with previous studies of training effects on contralateral limbs. 5. The abduction twitch force evoked by supramaximal electrical stimulations of the ulnar nerve was unchanged in all three groups after training, consistent with an absence of muscle hypertrophy. The maximal force of the left great toe extensors for individual subjects remained unchanged after training, which argues against strength increases due to general increases in effort level. 6. Increases in abduction and flexion forces of the fifth digit were poorly correlated in subjects of both training groups. The fifth finger abduction force and the hypothenar integrated EMG increases were not well correlated in these subjects either. Together these results indicate that training-induced changes of synergist and antagonist muscle activation patterns may have contributed to force increases in some of the subjects. 7. Strength increases can be achieved without repeated muscle activation. These force gains appear to result from practice effects on central motor programming/planning. The results of these experiments add to existing evidence for the neural origin of strength increases that occur before muscle hypertrophy.     

Back extensor and psoas muscle cross-sectional area, prior physical training, and trunk muscle strength – a longitudinal study in adolescent girls

The association between physical training, low back extensor (erector spinae plus multifidus muscles) and psoas muscle cross-sectional areas (CSA) and strength characteristics of trunk extension and flexion were studied in adolescent girls. A group of athletes (n=49) (age range 13.7–16.3 years) consisting of gymnasts, figure skaters and ballet dancers was age-matched with non-athletes (n=17) who acted as a sedentary control group. The CSA of psoas muscles and multifidus plus erector spinae muscles were measured from lumbar axial images by magnetic resonance imaging. Maximal trunk extension and flexion forces were measured in a standing position using a dynamometer and trunk musculature endurance was evaluated using static holding tests. When CSA were adjusted with body mass, the athletes showed significantly greater CSA in both muscles studied (psoas P?P?P?P?P?P?P?相似文献   

Neuromuscular adaptations and serum hormones in women during short-term intensive strength training

Summary The effects were investigated in ten women of intensive heavy resistance strength training lasting for 3 weeks on electromyographic (EMG) activity, muscle cross-sectional area (CSA) and voluntary force production characteristics of leg extensor muscles. Blood samples for the determinations of serum hormones were taken from five of the subjects. Significant increases occurred in the higher force portions of the isometric force-time curve with an increase of 9.7 (SD 8.4)% (P<0.01) in maximal peak force. An increase of 15.8 (SD 20.9)% (P<0.05) took place also in the maximal neural activation (integrated EMG) of the trained muscles, while an enlargement of 4.6 (SD 7.4)% (P<0.05) occurred in the CSA of the quadriceps femoris muscle. Maximal force per muscle CSA increased significantly (P<0.05). No statistically significant changes were observed during the training in the mean concentrations of serum testosterone, free testosterone, cortisol and sex hormone binding globulin (SHBG). The individual concentrations of serum testosterone: SHBG ratio correlated with the individual changes obtained during the training in the muscle CSA (r=0.99;P<0.01). The present findings in women indicated that the increases in maximal strength during short-term but intensive strength training were primarily due to the increased voluntary activation of the trained muscles, while muscle hypertrophy remained limited in magnitude. Large interindividual differences in women in serum testosterone concentrations could indicate corresponding differences in muscle hypertrophy and strength development even during a short-term but intensive strength training period.     

Changes in strength and cross sectional area of the elbow flexors as a result of isometric strength training

Summary Changes in strength and size of the elbow flexor muscles have been compared during six weeks of isometric strength training in six male and six female subjects. Isometric training of one arm resulted in a significant increase in isometric force (14.5±5.1%, mean±SD,n = 12). No differences were seen in the response of male and female subjects. The extent of the change was similar to that reported for training studies of other muscles, thus refuting the suggestion that the elbow flexors may be especially amenable to training. Biceps and brachialis cross-sectional area (CSA) was measured from mid-upper arm X-ray computerized tomography before and after training. Muscles increased in area (5.4±3.8%) but this was smaller than, and not correlated with, the increase in strength. The main change in the first six weeks of strength training was therefore an increase in the force generated per unit cross-sectional area of muscle. The arrangement of fibres in the biceps is nearly parallel to the action of the muscle and it is argued that the increase in force per unit cross-sectional area is unlikely to be due to changes in the pennation of the muscle fibres as has been suggested for other muscles.     

The role of metabolites in strength training

This study examined the role of high forces versus metabolic cost in the adaptations following strength training. Ten young, healthy male and female subjects trained one leg using concentric (CL) and the other using eccentric (EL) contractions of the quadriceps muscle for 20 weeks. EL used weights which were 35% higher than those used for CL. Isometric strength, and the length: tension and force: velocity relationship of the muscle were measured before and after training. Muscle cross-sectional area (CSA) was measured near the knee and hip using computed tomography. Increases in isometric strength were greater for CL compared to EL, the difference being significant with the knee at 1.57 rad (90°) [mean (SD), 43.7 (19.6)% vs 22.9 (9.8)%, respectively; P = 0.01]. Increases in isokinetic strength tended to be larger for EL, although the differences were not significant. Significant increases in CSA occurred near the hip for both EL and CL. These results suggest that metabolic cost, and not high forces alone, are involved in the stimuli for muscle hypertrophy and strength gains following high-resistance training.     

Energy cost of submaximal isometric contractions in cat fast and slow twitch muscles

The purpose of the present investigation was to compare the net energy cost incurred by cat soleus (slow twitch muscle) and medial gastrocnemius (predominantly fast twitch muscle) muscles for isometric contractions. For this, a computer-controlled sequential stimulation system was employed that enabled fused isometric contractions at frequencies of motor unit discharge within the normal physiological range. This allowed submaximal isometric contractions to be maintained at tensions of 10%, 25%, 50% and 75% of the initial strength of each muscle (tetanic tension of the unfatigued muscle determined at the beginning of each experiment). Total net energy cost was greater for the gastrocnemius than for the soleus muscle at each tension studied. For both muscles, the metabolism shifted toward anaerobic pathways at higher contraction tensions. But in comparison to the soleus muscle, the gastrocnemius muscle consistently had a greater percentage of its total net energy cost provided by anaerobic glycolysis rather than aerobic metabolism; for the gastrocnemius and soleus muscles the percent of the total metabolism from anaerobic pathways was 74% and 18% during the 10% contraction, and 96% and 84% during the 75% contraction for the medial gastrocnemius and soleus muscles respectively.     

Ageing is not associated with a decline in neuromuscular innervation or reduced specific force in men aged 20 and 50 years.

The exact mechanisms responsible for the decline in strength with age are yet to be completely elucidated. Three proposed mechanisms responsible for the detrimental effect of increasing age on strength include changes in muscle mass, specific force and/or neuromuscular innervation. Thus, the purpose of this investigation was to determine if the age-related reduction in peak isometric strength was primarily associated with changes in muscle cross-sectional area, neuromuscular innervation and/or specific force. The cross-sectional area of the knee extensor muscles (QCSA) was estimated in 13 younger men (YM; 20.8 +/- 1.6 years) and eight middle-aged men (MM; 53.8 +/- 4.2 years) prior to performing a series of four maximal voluntary isometric contractions on an isokinetic dynamometer at an angle of 60 degrees knee flexion. Peak force was determined and surface electromyography was sampled from the rectus femoris muscle during each maximal voluntary contraction. The cross-sectional area of the knee extensor muscles, peak force and integrated electromyography (IEMG) were significantly lower in the MM (P<0.01). However, when peak force and peak IEMG values were corrected for QCSA, there were no significant differences between age groups. These results suggest that the reduction in peak isometric force observed in the MM was primarily associated with quantitative changes in muscle mass, rather than reduced neuromuscular innervation or specific force. Therefore, preserving muscle mass through resistance training may significantly reduce the age-associated differences in peak strength and assist in promoting quality of life and functional independence in older adults.     

Strength and power changes of the human plantar flexors and knee extensors in response to resistance training in old age

AIM: The aim of the present study was to assess and compare the improvements of muscle strength and power induced by a 16-week resistive programme in a population of 16 older men aged 65-81 years. METHODS: Training was performed three times per week at an intensity of 80% of one repetition maximum (1RM) and consisted of both calf raise and leg press exercises. Before-, during- and after-training, maximum isometric and isokinetic torques, maximum power, 1RM, muscle cross-sectional area (CSA) and electromyographic activity (EMG) of the plantar flexors (PF) and knee extensors (KE) were examined. RESULTS: For the KE and PF, respectively, training resulted in a 29.9 +/- 4.4% (mean +/- SE) and 21.6 +/- 5.4% increase in 1RM (P < 0.001-0.01), a 19.4 +/- 4.3 and 12.4 +/- 4.7% (P < 0.001-0.05) increase in maximum isometric torque, and a 24.1 +/- 6.3 and 33.1 +/- 10.9% (P < 0.05) increase in maximum muscle power, calculated from torque-angular velocity curves. The large increase in torque and power was partly accounted by a significant increase in the CSA of the PF (5.0 +/- 0.7%) and KE (7.4 +/- 0.7%), while no significant changes in integrated EMG activity of vastus lateralis and soleus muscles, and in extrapolated maximum shortening velocity were found. After training, a significant increase in torque/CSA (10.3 +/- 4%, P < 0.05) was found for the KE but not for the PF. CONCLUSION: Hence, hypertrophy cannot alone justify the increase in torque, and other factors, such as an increase in individual fibre-specific tension (in the case of KE), a decrease in antagonist muscles' coactivation, an improved co-ordination and an increased neural drive of the other heads of quadriceps may have contributed to the increments in strength. The significant increase in muscle power seems particularly noteworthy with respect to daily activities involving the displacement of the body over time, namely, the generation of muscle power.     

Comparison of muscle hypertrophy following 6-month of continuous and periodic strength training

To compare the effects of a periodic resistance training (PTR) program with those of a continuous resistance training (CTR) program on muscle size and function, 14 young men were randomly divided into a CTR group and a PTR group. Both groups performed high-intensity bench press exercise training [75 % of one repetition maximum (1-RM); 3 sets of 10 reps] for 3 days per week. The CTR group trained continuously over a 24-week period, whereas the PTR group performed three cycles of 6-week training (or retraining), with 3-week detraining periods between training cycles. After an initial 6 weeks of training, increases in cross-sectional area (CSA) of the triceps brachii and pectoralis major muscles and maximum isometric voluntary contraction of the elbow extensors and 1-RM were similar between the two groups. In the CTR group, muscle CSA and strength gradually increased during the initial 6 weeks of training. However, the rate of increase in muscle CSA and 1-RM decreased gradually after that. In the PTR group, increase in muscle CSA and strength during the first 3-week detraining/6-week retraining cycle were similar to that in the CTR group during the corresponding period. However, increase in muscle CSA and strength during the second 3-week detraining/6-week retraining cycle were significantly higher in the PTR group than in the CTR group. Thus, overall improvements in muscle CSA and strength were similar between the groups. The results indicate that 3-week detraining/6-week retraining cycles result in muscle hypertrophy similar to that occurring with continuous resistance training after 24 weeks.     

Computer analysis of the surface EMG during isometric exercise

A computer program is described which can provide either on-line or off-line analysis of the surface electromyogram (EMG) in man during submaximal isometric contractions. The intention of the program was to quantify the tension developed by, and the degree of fatigue induced in muscle during this form of exertion from the surface EMG. Six male and female volunteers served as subjects to test the program by exerting brief isometric contractions of their handgrip muscles at tensions ranging from 3 to 100% of their maximum strength and fatiguing isometric contractions at tensions ranging between 20 and 95% of their maximum strength. The results of these experiments showed that the program was able to estimate the tension developed by muscle within an average of 2.4% of the subject's maximum strength and estimate the duration of fatigue contractions within an average of 3.5% of the actual recorded endurance. The applications of this form of analysis to work physiology are discussed.     

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.     

Muscle damage induced by electrical stimulation

Electrical stimulation (ES) induces muscle damage that is characterised by histological alterations of muscle fibres and connective tissue, increases in circulating creatine kinase (CK) activity, decreases in muscle strength and development of delayed onset muscle soreness (DOMS). Muscle damage is induced not only by eccentric contractions with ES but also by isometric contractions evoked by ES. Muscle damage profile following 40 isometric contractions of the knee extensors is similar between pulsed current (75 Hz, 400 μs) and alternating current (2.5 kHz delivered at 75 Hz, 400 μs) ES for similar force output. When comparing maximal voluntary and ES-evoked (75 Hz, 200 μs) 50 isometric contractions of the elbow flexors, ES results in greater decreases in maximal voluntary contraction strength, increases in plasma CK activity and DOMS. It appears that the magnitude of muscle damage induced by ES-evoked isometric contractions is comparable to that induced by maximal voluntary eccentric contractions, although the volume of affected muscles in ES is not as large as that of eccentric exercise-induced muscle damage. It seems likely that the muscle damage in ES is associated with high mechanical stress on the activated muscle fibres due to the specificity of motor unit recruitment (i.e., non-selective, synchronous and spatially fixed manner). The magnitude of muscle damage induced by ES is significantly reduced when the second ES bout is performed 2–4 weeks later. It is possible to attenuate the magnitude of muscle damage by “pre-conditioning” muscles, so that muscle damage should not limit the use of ES in training and rehabilitation.     

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