Effects of strength training and detraining on regional muscle in young and older men and women

To examine the effects of 9 weeks of strength training (ST) and 31 weeks of detraining on regional muscle area in young and older men and women, three regions of the quadriceps muscle area (proximal, middle, and distal) were measured via MRI in 11 men ages 20–30, 11 men ages 65–75, 10 women ages 20–30, and 11 women ages 65–75. These effects were assessed by determining the difference between the control limb and the trained limb (T-UT) at all three time points. This design provided control for possible influences of biological, methodological, seasonal variations, as well as influences due to attention or genetic differences that commonly occur between experimental and control groups. There were no significant differences in any of the three regions at any of the three time points, when comparing subjects by age. However, men had significantly greater T-UT CSA at the after ST time point [6.9 (3.7) cm²] when compared with women [2.8 (3.7) cm², P < 0.05]. Baseline T-UT CSA was higher than after detraining T-UT CSA for young men in the proximal and middle regions [0.1 (3.6), 0.4 (3.6) cm² vs. 2.8 (4.0), 2.4 (3.6) cm², P < 0.05], but there were no significant differences within the other three groups. These data indicate that sex may influence changes in regional CSA after ST, whereas age does not influence regional muscle gain or loss due to ST or detraining.     

Maximal force,force/time and activation/coactivation characteristics of the neck muscles in extension and flexion in healthy men and women at different ages

This study examined the force production characteristics, activation/coactivation and endurance capacity of the neck extension and flexion muscles in healthy men (n=29) and women (n=28) divided into three age groups (18–26 years, 30–37 years and 45–55 years). Force and electromyography (EMG) measurements were performed during the maximal voluntary isometric extension and flexion actions. This was followed by an endurance test (ET; 60% force level of maximal voluntary contraction sustained until exhaustion), after which the force and EMG recordings were repeated. Men were both stronger and had higher values (P<0.001) for explosive force (rate of force development, RFD) than women in both actions. Younger subjects of both genders exhibited larger (P<0.05 in women) RFD values than older subjects in extension. The coactivation of the antagonist muscles during the maximal extension or flexion did not differ significantly between men and women, but the coactivation of the antagonists was larger (P<0.05) in the older age groups than in the youngest group. Women maintained the 60% force level longer than men in both actions (extension, P<0.001; flexion, not significant). The fatiguing loading led to significant decreases in maximal isometric force (P<0.001) and RFD (P<0.01–0.001), but these relative decreases did not differ between the groups. In conclusion, large gender differences in the voluntary extension and flexion force production characteristics of the neck muscles did exist, as reported earlier for other muscles of the body. No age-related differences were observed in maximal force of the extension and flexion actions within the age ranges of the subject groups studied here, but the older subjects exhibited greater coactivation and produced lower force values in the early portions of the force/time curve of the extension than the youngest group. The data indicate that explosive force production may be sensitive to aging earlier than maximal strength in the case of the neck extensor muscles. Electronic Publication     

Contributions of force and velocity to improved power with progressive resistance training in young and older adults

We investigated the effects of age on changes in the force and velocity components of knee extension (KE) power during 16 weeks of traditional progressive resistance training (PRT). Thirty-one young (27 ± 1 years, 16 men, 15 women) and 30 older (64 ± 1 years, 14 men, 16 women) adults trained by KE, leg press, and squat 3 days/week. PRT consisted of three sets with an appropriate load for 8–12 repetitions to fatigue. Testing occurred at baseline, 8, and 16 weeks. Thigh lean mass (TLM) was measured by DEXA. KE load–power and load–velocity curves were generated from peak concentric contractions against loads equivalent to 20, 30, 40, 50, and 60% maximum voluntary isometric contraction (MVC) force. Quadriceps neural activation relative to maximum was assessed during a sit-to-stand task. Participants increased KE 1RM (P < 0.05) by 8 weeks with young adults also increasing strength from 8 to 16 weeks. Adjusting for TLM, all groups increased KE specific strength (P < 0.05). MVC improved by 8 weeks in older adults and by 16 weeks in young subjects (P < 0.05). Neural activation requirements during standing and sitting declined in older adults by 8 weeks (P < 0.05). The KE load–power curve improved for all groups (P < 0.05) by 8 weeks with only young adults improving from 8 to 16 weeks. Peak concentric velocity increased only in older adults (P < 0.05). Training improvements in power resulted primarily from increases in strength both early and late for young adults while older adults realized early improvements in both strength and peak concentric velocity. Grants: This study was supported by National Institute on Aging Grant R01 AG017896 (MMB), Department of Veterans’ Affairs Merit Grant (MMB), and General Clinical Research Center Grant M01 RR00032.     

High-intensity endurance training improves adiponectin mRNA and plasma concentrations

Adiponectin is an anti-inflammatory protein that reduced in obesity. Exercise training may reduce the adipose tissue (AT), although it is not well known whether exercise-induced change in AT, increases the adiponectin mRNA expression and plasma concentrations or not; therefore, the purpose of this study was to investigate the adiponectin mRNA and plasma concentrations in middle-aged men after 12 weeks high-intensity exercise training and after a week detraining. Sixteen sedentary overweight and obese middle-aged men (age 41.18 ± 6.1 years; ± SD) volunteered to participate in this study. The subjects were randomly assigned to training group (n = 8) or control group (n = 8). The training group performed endurance training 4 days a week for 12 weeks at an intensity corresponding to 75–80% individual maximum oxygen consumption for 45 min. After 12 weeks of training, subjects underwent a week of detraining. The results showed that the BMI as well as central and peripheral AT volume were decreased in the training group compared to the control group (P < 0.05). After 12 weeks, the training group resulted in a significant increase (P < 0.05) in the adiponectin gene expression in abdominal and gluteal subcutaneous AT when compared with the control group. The results showed that plasma adiponectin concentrations increased and insulin resistance decreased after training compared to the control group (P < 0.05). After a week of detraining, the variables were not changed significantly in the training group. In conclusion, high-intensity endurance training caused an increase adiponectin mRNA in obese middle-aged men.     

Age-related differences in rapid muscle activation after rate of force development training of the elbow flexors

In young adults, improvements in the rate of force development as a result of resistance training are accompanied by increases in neural drive in the very initial phase of muscle activation. The purpose of this experiment was to determine if older adults also exhibit similar adaptations in response to rate of force development (RFD) training. Eight young (21–35 years) and eight older (60–79 years) adults were assessed during the production of maximum rapid contractions, before and after four weeks of progressive resistance training for the elbow flexors. Young and older adults exhibited significant increases (P<0.01) in peak RFD, of 25.6% and 28.6% respectively. For both groups the increase in RFD was accompanied by an increase in the root mean square (RMS) amplitude and in the rate of rise (RER) in the electromyogram (EMG) throughout the initial 100 ms of activation. For older adults, however, this training response was only apparent in the brachialis and brachioradialis muscles. This response was not observed in surface EMG recorded from the biceps brachii muscle during either RFD testing or throughout training, nor was it observed in the pronator teres muscle. The minimal adaptations observed for older adults in the bifunctional muscles biceps brachii and pronator teres are considered to indicate a compromise of the neural adaptations older adults might experience in response to resistance training.     

The rate of force development scaling factor (RFD-SF): protocol,reliability, and muscle comparisons

Performing a set of isometric muscular contractions to varied amplitudes with instructions to generate force most rapidly reveals a strong linear relationship between peak forces (PF) achieved and corresponding peak rates of force development (RFD). The slope of this relationship, termed the RFD scaling factor (RFD-SF), quantifies the extent to which RFD scales with contraction amplitude. Such scaling allows relative invariance in the time required to reach PF regardless of contraction size. Considering the increasing use of this relationship to study quickness and consequences of slowness in older adults and movement disorders, our purpose was to further develop the protocol to measure RFD-SF. Fifteen adults (19–28 years) performed 125 rapid isometric contractions to a variety of force levels in elbow extensors, index finger abductors, and knee extensors, on 2 days. Data were used to determine (1) how the number of pulses affects computation of the RFD-SF, (2) day-to-day reliability of the RFD-SF, and (3) the nature of RFD-SF differences between diverse muscle groups. While sensitive to the number of pulses used in its computation (P < .05), RFD-SF was reliable when computed with >50 pulses (ICC > .7) and more so with 100–125 pulses (ICC = .8–.92). Despite differences in size and function across muscles, RFD-SF was generally similar (i.e., only 8.5% greater in elbow extensors than in index finger abductors and knee extensors; P = .049). Results support this protocol as a reliable means to assess how RFD scales with PF in rapid isometric contractions as well as a simple, non-invasive probe into neuromuscular health.     

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.     

Change in post-exercise vagal reactivation with exercise training and detraining in young men

We studied the effects of aerobic exercise training and detraining in humans on post-exercise vagal reactivation. Ten healthy untrained men trained for 8 weeks using a cycle ergometer [70% of initial maximal oxygen uptake ( ) for 1 h, 3–4 days·week^–1] and then did not exercise for the next 4 weeks. Post-exercise vagal reactivation was evaluated as the time constant of the beat-by-beat decrease in heart rate during the 30 s (t₃₀) immediately following 4 min exercise at 80% of ventilatory threshold (VT). The and the oxygen uptake at VT had significantly increased after the 8 weeks training programme (P<0.0001, P<0.001, respectively). The t₃₀ had shortened after training, and values after 4 weeks and 8 weeks of training were significantly shorter than the initial t₃₀ (P<0.05, P<0.01, respectively). The change in the t₃₀ after 8 weeks of training closely and inversely correlated with the initial t₃₀ (r=–0.965, P<0.0001). The reduced t₃₀ was prolonged significantly after 2 weeks of detraining, and had returned almost to the baseline level after a further 2 weeks of detraining. These results suggest that aerobic exercise training of moderate intensity accelerates post-exercise vagal reactivation, but that the accelerated function regresses within a few weeks of detraining. Electronic Publication     

Effect of electrostimulation training–detraining on neuromuscular fatigue mechanisms

The aim of this study was to evaluate the effects of neuromuscular electrical stimulation (NMES) training and subsequent detraining on neuromuscular fatigue mechanisms. Ten young healthy men completed one NMES fatigue protocol before and after a NMES training program of 4 weeks and again after 4 weeks of detraining. Muscle fatigue (maximal voluntary torque loss), central fatigue (activation failure), and peripheral fatigue (transmission failure and contractile failure) of the plantar flexor muscles were assessed by using a series of electrically evoked and voluntary contractions with concomitant electromyographic and torque recordings. At baseline, maximal voluntary torque decreased significantly with fatigue (P < 0.001), due to both activation and transmission failure. After detraining, maximal voluntary torque loss was significantly reduced (P < 0.05). In the same way, the relative decrease in muscle activation after training and detraining was significantly lower compared to baseline values (P < 0.05). Short-term NMES training–detraining of the plantar flexor muscles significantly reduced the muscle fatigue associated to one single NMES exercise session. This was mainly attributable to a reduction in activation failure, i.e., lower central fatigue, probably as a result of subject's accommodation to pain and discomfort during NMES.     

Impact of sensorimotor training on the rate of force development and neural activation

The ability to generate high muscular strength within short time periods is of functional importance not only as a basic quality in many sports disciplines but also for active stabilization of joints. The rate of force development (RFD) is generally used to describe this ability. The purpose of the present study was to examine the functional adaptations of a specific sensorimotor training on the explosive strength qualities of the leg extensor muscles during maximum isometric actions. Force and surface EMG were recorded in 17 subjects before and after a 4-week sensorimotor training period. Maximum static leg press strength did not change [608.2 (47.0) N to 627.8 (48.4) N before/after training], whereas maximum RFD (RFD_max) increased significantly from 4.95 (0.48) N/ms to 6.58 (0.76) N/ms (P<0.05). The gain in RFD_max was accompanied by an increased EMG of the M. vastus medialis. Enhancement of neuromuscular activation was only prominent in the early phases of muscular action. Neither force nor EMG parameters revealed significant improvements for time phases beyond 100 ms following the onset of isometric action. Enhanced extrafacilitatory drive from the afferent system is discussed as a potential mechanism for the improved neural activation. From a more functional point of view, this type of adaptation may be helpful in various sport performances. Moreover, with regard to injury related situations, enhanced neuromuscular activation is of distinct relevance in order to stiffen joint complexes actively within short time periods.     

Maximal strength training improves work economy, rate of force development and maximal strength more than conventional strength training

This study compared maximal strength training (MST) with equal training volume (kg × sets × repetitions) of conventional strength training (CON) primarily with regard to work economy, and second one repetition maximum (1RM) and rate of force development (RFD) of single leg knee extension. In an intra-individual design, one leg was randomized to knee-extension MST (4 or 5RM) and the other leg to CON (3 × 10RM) three times per week for 8 weeks. MST was performed with maximal concentric mobilization of force while CON was performed with moderate velocity. Eight untrained or moderately trained men (26 ± 1 years) completed the study. The improvement in gross work economy was ?0.10 ± 0.08 L min^?1 larger after MST (P = 0.011, between groups). From pre- to post-test the MST and CON improved net work economy with 31 % (P < 0.001) and 18 % (P = 0.01), respectively. Compared with CON, the improvement in 1RM and dynamic RFD was 13.7 ± 8.4 kg (P = 0.002) and 587 ± 679 N s^?1 (P = 0.044) larger after MST, whereas isometric RFD was of borderline significance 3,028 ± 3,674 N s^?1 (P = 0.053). From pre- to post-test, MST improved 1RM and isometric RFD with 50 % (P < 0.001) and 155 % (P < 0.001), respectively whereas CON improved 1RM and isometric RFD with 35 % (P < 0.001) and 83 % (P = 0.028), respectively. Anthropometric measures of quadriceps femoris muscle mass and peak oxygen uptake did not change. In conclusion, 8 weeks of MST was more effective than CON for improving work economy, 1RM and RFD in untrained and moderately trained men. The advantageous effect of MST to improve work economy could be due to larger improvements in 1RM and RFD.     

Cross education of muscular strength during unilateral resistance training and detraining

Abstract. The purpose of the present study was to examine the changes in maximum voluntary isometric contraction (MVC) in the contralateral untrained limb during unilateral resistance training and detraining, and to examine the factors inducing these changes by means of electrophysiological techniques. Nine healthy males trained their plantar flexor muscles unilaterally 4 days·week^–1 for 6 weeks using 3 sets of 10–12 repetitions at 70–75% of one-repetition maximum a day, and detrained for 6 weeks. Progressive unilateral resistance training significantly (P<0.05) increased MVC, integrated electromyogram (iEMG), and voluntary activation in the trained and contralateral untrained limbs. The changes in MVC after training were significantly correlated with the changes in iEMG in both limbs. No significant changes occurred in MVC, voluntary activation, and iEMG in the contralateral limb after detraining. The changes in MVC after detraining did not correlate with the changes in voluntary activation or iEMG in either limb. Training and detraining did not alter twitch and tetanic peak torques in either limb. These results suggest that the mechanisms underlying cross education of muscular strength may be explained by central neural factors during training, but not solely so during detraining. Electronic Publication     

Late neural adaptations to electrostimulation resistance training of the plantar flexor muscles

The present study aimed to examine early and late neural adaptations to short-term electrostimulation training of the plantar flexor muscles. Changes in triceps surae muscle activation (twitch interpolation), maximal electromyographic (EMG) activity, H-reflex amplitudes and antagonist coactivation were investigated after electrostimulation training (4 weeks) and after 4 weeks of detraining in a group of ten young healthy men. Maximal voluntary contraction torque was significantly higher (P < 0.01) after training (+19.4%) and detraining (+17.2%) with respect to baseline. Activation level, soleus and lateral gastrocnemius EMG normalized to the maximal M-wave significantly increased as a result of training (P < 0.05), and these gains were preserved after detraining, excepted for soleus EMG. Maximal H reflex to maximal M wave ratio increased significantly between baseline and detraining for both soleus and lateral gastrocnemius muscles (P < 0.05). Tibialis anterior coactivation was unchanged after training but significantly decreased after the detraining period (P < 0.01). Short-term electrostimulation resistance training was accompanied by early (increased muscle activation and EMG activity) and late neural adaptations (increased spinal reflex amplitude and decreased coactivation), likely explaining the increase and then the preservation of the maximal voluntary strength. These effects may help in conceiving and programming effective electrostimulation therapy programs for both healthy and immobilized plantar flexor muscles.     

Effect of different resistance-training regimens on the WNT-signaling pathway

The purpose of the present study was to evaluate the effects of 8 weeks of strength and power training on the expression of genes related to the canonical WNT pathway and β-catenin protein levels in physically active men. Twenty-five subjects (27.4 ± 4.6 years) were balanced based on their relative maximum strength in the squat exercise (squat 1RM/body mass) and randomly assigned to strength training (ST) (n = 10), power training (PT) (n = 10), and control (C) (n = 5) groups. The ST and the PT groups performed high and low intensity squats, respectively, thrice a week, for 8 weeks. Muscle biopsies from the vastus lateralis muscle were collected before and after the training period. Relative strength and power increased similarly in both ST and PT groups (P < 0.001). Fiber cross-sectional area also increased similarly in both ST and PT groups. Gene expression and β-catenin protein expression levels were assessed by real-time PCR and Western blot. Certain genes were up-regulated in the ST group (WNT1: 6.4-fold, P < 0.0001; SFRP1: 3.3-fold, P < 0.0001 and LEF1: 7.3-fold, P < 0.0001) and also in the PT group (WNT1: 24.9-fold, P < 0.0001; SFRP1: 2.7-fold, P < 0.0001; LEF1: 34.1-fold, P < 0.0001 and Cyclin D1: 7.7-fold, P < 0.001). In addition, the expression of key WNT pathway genes was substantially more responsive to PT than to ST (WNT1: P < 0.0001; LEF1: P < 0.0001 and Cyclin D1: P < 0.001). Finally, the total β-catenin protein content increased only in the PT group (P < 0.05). Our data indicate that a PT regimen triggers greater responses in key elements of the WNT pathway.     

Rapid vascular modifications to localized rhythmic handgrip training and detraining

Despite the evidence describing the rapid vascular function modifications to commencement and cessation of large muscle exercises (i.e. cycling), no studies examined the time-course vascular modifications to localized training and detraining. This study aimed to examine the effects of 4-week rhythmic handgrip exercise training and 2-week detraining on reactive hyperemic forearm blood flow and vascular resistance in 11 young men. Rhythmic handgrip exercise was performed in the non-dominant forearm for 20 min/day, 5 days/week, at 60% of maximum voluntary contraction for 4 weeks, followed by 2 weeks of no training. Forearm blood flow and vascular resistance were evaluated, in both arms, at rest and following arterial occlusion. These vascular function indices were obtained in five visits; before, after 1 and 4 week(s) of training as well as after 1 and 2 week(s) of training cessation. Resting cardiovascular measures were not altered during the study period. A 2 (arms) × 5 (visits) ANOVA revealed significant arms-by-visits interactions for reactive hyperemic forearm blood flow (p = 0.02) and vascular resistance (p = 0.02). Subsequent comparison demonstrated increased trained forearm reactive hyperemic blood flow 1 week after training, then returned to pre-training values 1 week following training cessation. In contrast, vascular resistance decreased 1 week after training commencement, only to return to pretraining level 1 week after training cessation. These results indicate a rapid, unilateral improvement in regional reactive hyperemic blood flow and vascular resistance following localized exercise-training. However, the improvements are transient and return to pretraining levels 1 week after detraining.     

Interrelationships between electromyographic,mechanical, muscle structure and reflex time measurements in man

Reaction time (TRT) with its premotor (PMT) and motor time (MT) components, patellar reflex time (TRfT) with its latency (LAT) and motor time (RfMT) were studied together with isometric force production and relaxation time variables in one leg isometric knee extension. These variables were intercorrelated together with muscle biopsy variables taken from m. vastus lateralis. From these computations MT proved to demonstrate significant correlations to rate of isometric force development (RFD) (P<0.001), maximum force (P₀) (P<0.001) and per cent distribution of ST fibers (P<0.001). It is speculated that these relationships are determined by the pattern of the motor unit recruitment and by different characteristics of the slow and fast twitch muscle fibers to trigger the excitation-contraction coupling.     

High volume of endurance training impairs adaptations to 12 weeks of strength training in well-trained endurance athletes

The purpose of the present study was to compare the effect of 12 weeks of strength training combined with a large volume of endurance training with the effect of strength training alone on the strength training adaptations. Well-trained cyclists with no strength training experience performed heavy strength training twice a week in addition to a high volume of endurance training during a 12-week preparatory period (S + E; n = 11). A group of non-strength trained individuals performed the same strength training as S + E, but without added endurance training (S; n = 7). Thigh muscle cross-sectional area, 1 repetition maximum (1RM) in leg exercises, squat jump performance, and peak rate of force development (RFD) were measured. Following the intervention period, both S + E and S increased 1RM strength, thigh muscle cross-sectional area, and squat jump performance (p < 0.05), and the relative improvements in S were greater than in S + E (p < 0.05). S increased peak RFD while S + E did not, and this improvement was greater than in S + E (p < 0.05). To the best of our knowledge, this is the first controlled study to demonstrate that the strength training response on muscle hypertrophy, 1RM strength, squat jump performance, and peak RFD is attenuated in well-trained endurance athletes during a period of concurrent endurance training.     

Lipid and lipoprotein profiles, cardiovascular fitness, body composition, and diet during and after resistance, aerobic and combination training in young women

The purpose of this study was to evaluate the effects of various modes of training on the time-course of changes in lipoprotein-lipid profiles in the blood, cardiovascular fitness, and body composition after 16 weeks of training and 6 weeks of detraining in young women. A group of 48 sedentary but healthy women [mean age 20.4 (SD 1) years] were matched and randomly placed into a control group (CG, n=12), an aerobic training group (ATG, n=12), a resistance training group (RTG, n=12), or a cross-training group that combined both aerobic and resistance training (XTG, n=12). The ATG, RTG and XTG trained for 16 weeks and were monitored for changes in blood concentrations of lipoprotein-lipids, cardiovascular fitness, body composition, and dietary composition throughout a 16 week period of training and 6 weeks of detraining. The ATG significantly reduced blood concentrations of triglycerides (TRI) (P < 0.05) and significantly increased blood concentrations of high-density lipoprotein-cholesterol (HDL-C) after 16 weeks of training. The correlation between percentage fat and HDL-C was 0.63 (P < 0.05), which explained 40% of the variation in HDL-C, while the correlation between maximal oxygen uptake (V˙O_2max) and HDL-C was 0.48 (P < 0.05), which explained 23% of the variation in HDL-C. The ATG increased V˙O_2max by 25% (P < 0.001) and decreased percentage body fat by 13% (P < 0.05) after 16 weeks. Each of the alterations in the ATG had disappeared after the 6 week detraining period. The concentration of total cholesterol (TC), TRI, HDL-C and low density lipoprotein-cholesterol in the blood did not change during the study in RTG, XTG and CG. The RTG increased upper and lower body strength by 29% (P < 0.001) and 38%, respectively. The 6 week detraining strength values obtained in RTG were significantly greater than those obtained at baseline. The XTG increased upper and lower body strength by 19% (P < 0.01) and 25% (P < 0.001), respectively. The 6 week detraining strength values obtained in XTG were significantly greater than those obtained at baseline. The RTG, XTG and CG did not demonstrate any significant changes in either V˙O_2max, or body composition during the training and detraining periods. The results of this study suggest that aerobic-type exercise improves lipoprotein-lipid profiles, cardiorespiratory fitness and body composition in healthy, young women, while resistance training significantly improved upper and lower body strength only. Accepted: 9 April 2000     

Electromyogram changes during sustained contraction after resistance training in women in their 3rd and 8th decades

The present study aimed at investigating the neuromuscular adaptations to 6 weeks of resistance training in women in their third (6 experimental, 8 controls) and eighth decades (8 experimental, 8 controls). The surface electromyogram (sEMG) was measured from the biceps brachii muscle during constant-force isometric contractions lasting 12 s at 80% of maximal voluntary contraction (MVC). All the signals were analysed adopting in the time domain the root mean square (RMS) as a measure of amplitude and in the frequency domain the median frequency (MDF) of the power spectrum. Quantitative analysis was performed from the 3rd to the 6th second, to describe the early phase of the contraction (“Early”), starting from point at which 80% of the MVC was reached, and from the 9th to the 12th second, to describe the last part of the constant-force sustained contraction (“Late”). After training, the MVC increased by 22.4% in the young (P < 0.0001) and by 13.4% in the older (P < 0.05) women. The “Early” RMS increased by 60.4% with respect to the pre-training condition in the young (P < 0.01) but not in the older women. In contrast, the “Late” RMS increased by 46.7% in the older (P < 0.05) but not in the young women. The MDF remained unchanged in both groups. These results indicate that young and older women showed different training-induced adaptation of the motor unit (MU) activation pattern, in order to keep a constant level of force during a sustained isometric contraction at 80% of MVC. Accepted: 11 March 2000