Neural Adaptations to Resistive Exercise

Effect of 16 weeks of resistance training on fatigue resistance in men and women

The purpose of this study was to investigate the effect of hypertrophy-type resistance training (RT) on upper limb fatigue resistance in young adult men and women. Fifty-eight men (22.7±3.7 years, 70.6±9.3 kg, and 176.8±6.4 cm) and 65 women (21.6±3.7 years, 58.8±11.9 kg, and 162.6±6.2 cm) underwent RT for 16 weeks. Training consisted of 10–12 whole body exercises with 3 sets of 8–12 repetitions maximum performed 3 times per week. Before and after the RT intervention participants were submitted to 1RM testing, as well as a fatigue protocol consisting of 4 sets at 80% 1RM on bench press (BP) and arm curl (AC). The sum of the number of repetitions accomplished in the 4 sets in each exercise was used to indicate fatigue resistance. There was a significant (p<0.05) time-by-group interaction in 1RM BP (men=+16%, women=+26%), however in 1RM AC no significant time-by-group interaction was observed (men=+14%, women=+23%). For the total number of repetitions, men and women showed a significant increase in BP (men=+16.3%, women=+10.5%) with no time-by-group interaction. The results suggest that the adaptation in maximal strength is influenced by sex in BP. On the other hand, for fatigue resistance, the individual’s sex does not seem to influence outcomes either in BP or AC.

Avoiding Systematic Errors in Isometric Squat-Related Studies without Pre-Familiarization by Using Sufficient Numbers of Trials

There is no scientific evidence in the literature indicating that maximal isometric strength measures can be assessed within 3 trials. We questioned whether the results of isometric squat-related studies in which maximal isometric squat strength (MISS) testing was performed using limited numbers of trials without pre-familiarization might have included systematic errors, especially those resulting from acute learning effects. Forty resistance-trained male participants performed 8 isometric squat trials without pre-familiarization. The highest measures in the first “n” trials (3 ≤ n ≤ 8) of these 8 squats were regarded as MISS obtained using 6 different MISS test methods featuring different numbers of trials (The Best of n Trials Method [BnT]). When B3T and B8T were paired with other methods, high reliability was found between the paired methods in terms of intraclass correlation coefficients (0.93–0.98) and coefficients of variation (3.4–7.0%). The Wilcoxon’s signed rank test indicated that MISS obtained using B3T and B8T were lower (p < 0.001) and higher (p < 0.001), respectively, than those obtained using other methods. The Bland-Altman method revealed a lack of agreement between any of the paired methods. Simulation studies illustrated that increasing the number of trials to 9–10 using a relatively large sample size (i.e., ≥ 24) could be an effective means of obtaining the actual MISS values of the participants. The common use of a limited number of trials in MISS tests without pre-familiarization appears to have no solid scientific base. Our findings suggest that the number of trials should be increased in commonly used MISS tests to avoid learning effect-related systematic errors.

Effects of involuntary eccentric contraction training by neuromuscular electrical stimulation on the enhancement of muscle strength

BACKGROUND

Neuromuscular electrical stimulation is well-known as a modality to improve the performance of neuromuscular system, but its clinical value on muscle strengthening remains equivocal. In this study, we designed a system for an involuntary eccentric contraction of biceps brachii muscles using continuous passive movement and commercial neuromuscular electrical stimulation devices.

METHODS

To investigate the effects of involuntary eccentric contraction training by neuromuscular electrical stimulation on the enhancement of muscle strength, seven healthy men between the ages of 24 and 29 years participated in this study. Participants were trained two times per week for 12 weeks. Each exercise session was performed for 30 min with no rest intervals. Isometric elbow flexion torque and biceps brachii muscle thickness were chosen as evaluation indices, and were measured at pre-/post-training.

FINDINGS

After the 12-week training, the isometric elbow flexion torque of the trained side significantly increased by approximately 23% compared to the initial performance (P<0.01). Meanwhile, the torque of the untrained side showed no significant change (P=0.862). During the 12-week training period, the biceps brachii muscle thickness of the trained side significantly increased by around 8% at rest and 16% at maximum voluntary contraction (P<0.01).

INTERPRETATION

The developed system and the technique show promising results, suggesting that it has the potential to be used to increase the muscle strength in patients with neuromuscular disease and to be implemented in design rehabilitative protocols.

Analysis of the training load during a hypertrophy-type resistance training programme in men and women

The purpose of this study was to analyze the specific training load during a resistance training (RT) programme designed to increase muscular hypertrophy in men and women. Thirty-four women (22.7 ± 4.1 years, 58.8 ± 11.9 kg, 162.6 ± 6.2 cm and 22.1 ± 3.6 kg.m(-2)) and 30 men (22.7 ± 4.4 years, 68.4 ± 9.0 kg, 174.5 ± 6.6 cm and 22.5 ± 2.4 kg.m(-2)) underwent a supervised RT programme that was divided into two phases of 8 weeks each. Training consisted of 10-12 exercises performed with three sets of 8-12 repetitions at repetition maximum resistances performed 3 times per week on nonconsecutive days. There was a significant (P < 0.05) main effect for gender by time interaction for average training load of all the exercises performed in the first 8 weeks of RT with women showing a higher relative increase than men (+43.6% vs. +32.5%, respectively). This result was not observed during the second 8-week phase of the RT programme during which no significant gender by time interaction (P > 0.05) was shown with both genders having a similar relative increase (+28.7% vs. +24.3%, respectively). Women had a higher increase than men in specific average training load of the upper limb exercises during both the first 8 weeks of training (+30.2% vs. +26.6%, respectively) and the second 8 weeks of training (+31.1% vs. +25.3%, respectively). We conclude that the adaptation in specific training load is influenced by gender.

Early-phase musculoskeletal adaptations to different levels of eccentric resistance after 8 weeks of lower body training

PURPOSE

Eccentric muscle actions are important to the development of muscle mass and strength and may affect bone mineral density (BMD). This study's purpose was to determine the relative effectiveness of five different eccentric:concentric load ratios to increase musculoskeletal parameters during early adaptations to resistance training.

METHODS

Forty male subjects performed a supine leg press and calf press training program 3 days week(-1) for 8 weeks. Subjects were matched for pre-training leg press 1-repetition maximum strength (1-RM) and randomly assigned to one of five training groups. Concentric training load (% 1-RM) was constant across groups, but within groups, eccentric load was 0, 33, 66, 100, or 138% of concentric load. Muscle mass (dual energy X-ray absorptiometry; DXA), strength (1-RM), and BMD (DXA) were measured pre- and post-training. Markers of bone metabolism were assessed pre-, mid- and post-training.

RESULTS

The increase in leg press 1-RM in the 138% group (20 ± 4%) was significantly greater (P < 0.05) than the 0% (8 ± 3%), 33% (8 ± 5%) and 66% (8 ± 4%) groups, but not the 100% group (13 ± 6 %; P = 0.15). All groups, except the 0% group, increased calf press 1-RM (P < 0.05). Leg lean mass and greater trochanter BMD were increased only in the 138% group (P < 0.05).

CONCLUSIONS

Early-phase adaptations to eccentric overload training include increases in muscle mass and site-specific increases in BMD and muscle strength which are not present or are less with traditional and eccentric underload training. Eccentric overload provides a robust musculoskeletal stimulus that may benefit bedridden patients, individuals recovering from injury or illness, and astronauts during spaceflight.

Time course of functional and biomechanical improvements during a gait training intervention in persons with chronic stroke

BACKGROUND AND PURPOSE

In rehabilitation, examining how variables change over time can help define the minimal number of training sessions required to produce a desired change. The purpose of this study was to identify the time course of changes in gait biomechanics and walking function in persons with chronic stroke.

METHODS

Thirteen persons who were more than 6 months poststroke participated in 12 weeks of fast treadmill training combined with plantar- and dorsiflexor muscle functional electrical stimulation (FastFES). All participants completed testing before the start of intervention, after 4, 8, and 12 weeks of FastFES locomotor training.

RESULTS

Peak limb paretic propulsion, paretic limb propulsive integral, peak paretic limb knee flexion (P < 0.05 for all), and peak paretic trailing limb angle (P < 0.01) improved from pretraining to 4 weeks but not between 4 and 12 weeks. Self-selected walking speed and 6-minute walk test distance improved from pretraining to 4 weeks and from 4 to 12 weeks (P < 0.01 and P < 0.05, respectively for both). Timed Up & Go test time did not improve between pretraining and 4 weeks, but improved by 12 weeks (P = 0.24 and P < 0.01, respectively).

DISCUSSION AND CONCLUSIONS

The results demonstrate that walking function improves with a different time course compared with gait biomechanics in response to a locomotor training intervention in persons with chronic stroke. Thirty-six training sessions were necessary to achieve an increase in walking speed that exceeded the minimally clinically important difference. These findings should be considered when designing locomotor training interventions after stroke.Video Abstract available (see Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A63) for more insights from the authors.

Immediate effects and short-term retention of multi-modal instruction compared to written only on muscle activity during the prone horizontal abduction exercise in individuals with shoulder pain

In rehabilitation, exercise instructions are multi-modal and can include a focus of increasing mean activity of a target muscle and inhibiting aberrant synergistic muscle activity, particularly during shoulder exercises, such as the prone horizontal abduction (PHA). The objective was to compare the immediate effects and short-term retention of multi-modal exercise instruction by a physical therapist written only instruction on normalized mean upper and lower trapezius muscle activity during three phases (concentric/isometric/eccentric) versus of an isotonic PHA exercise between participants with and without shoulder pain. Surface electromyography (EMG) was recorded from fourteen healthy participants and twelve participants with shoulder pain during the PHA exercise under two conditions: (1) written only instructions and (2) multi-modal instruction. Retention of multi-modal instruction on muscle activity was assessed one week later. Results demonstrate 12.8-16.0% increase in lower trapezius muscle activity during the concentric and isometric phases with multi-modal instructions in both groups. Inhibition of the upper trapezius did not occur in either group. Facilitation effects were maintained in short-term follow-up. Findings suggest that regardless of shoulder pain, multi-modal instruction by a physical therapist facilitates greater neuromuscular activity of a targeted muscle compared to written instructions alone and these effects are retained.

Effectiveness of accommodation and constant resistance training on maximal strength and power in trained athletes

Accommodation resistance is a training technique that may improve strength and power gains beyond those achieved by traditional free weights. In this method, chains are either added on a free-weight bar and combined with traditional plates or added to the bar as the entire load.

Purpose. The aim of the current study was to compare the effectiveness of accommodation and constant resistance training methods during a four-week period on maximal strength and power in trained athletes.

Methods. This study was comprised of 24 trained athletes, including 16 trained males [8 Wushu athletes (Kung-Fu) and 8 wrestlers, age: 20.5 ± 2.00 yrs. old]. Participants were initially tested on weight, body circumference, fat percent, upper and lower body maximal strength, determined by the 1-repetition maximum (1RM) test, which determines the greatest amount of weight a person can successfully lift, and upper and lower body power. Participants were equally randomized to either accommodation or constant resistance training groups. Both groups underwent resistance training for a four-week period that consisted of three sessions per week. Multivariate repeated-measures analyses of variance of the data were used to verify significant differences in strength and power between groups. The modified Bonferroni post hoc test was used to compare the obtained results in pre-, mid-, and post test.

Results. In the accommodation resistance group, there was a significant difference in lower body maximal strength compared to the constant group (163.12 ± 18.82 kg in the accommodation group vs. 142.25 ± 20.04 kg in the constant group, P = 0.04). No significant differences were found in upper body power, lower body power, and upper body maximal strength between the two groups (P > 0.05).

Conclusion. Although there was only a significant difference in lower body maximal strength between groups, accommodation resistance training may induce a physiological training response by improving the strength and power of stabilizing muscle groups required to balance the bar if consistently used over time.

Frequency and pattern of voluntary pedalling is influenced after one week of heavy strength training

Changes in voluntary rhythmic leg movement characteristics of freely chosen cadence (reflecting movement frequency) and tangential pedal force profile (reflecting movement pattern) were investigated during 4weeks of (i) heavy hip extension strength training (HET, n=9), (ii) heavy hip flexion strength training (HFT, n=9), and (iii) no intervention (CON, n=9). Training consisted of three 5RM-10RM sets per session, with two sessions/week. Submaximal ergometer cycling was performed before the training period (pretest) and after every week of training (test A1, A2, A3, and posttest). Strength increased by on average 25% in HET and 33% in HFT. Freely chosen cadence was only changed in HET, occurring already after 1week of training. Thus, percentage reductions of cadence in HET at test A1, A2, A3, and posttest, with respect to the pretest value, amounted for maximally on average 17%, or 14rpm, and were larger than the corresponding changes in CON (p=.037). Percentage increases in minimum tangential pedal force in HET at test A1, A2, A3, and posttest, with respect to the pretest value, were larger than the corresponding changes in CON (p=.024). Heavy hip flexion strength training did not cause such alterations.

Efeito do treino isocinético excêntrico sobre a razão I/Q do torque e EMGs em sujeitos saudáveis

OBJETIVO: Avaliar os efeitos do treino isocinético excêntrico dos extensores do joelho sobre a razão Isquiotibiais/Quadríceps (I/Q) do torque e do eletromiograma de superfície (EMGs), em sujeitos saudáveis.MÉTODOS: Vinte homens ativos e saudáveis com idade média 22,5±2,1 anos; massa corporal 67,8±9,5 kg; estatura 1,72±0,10 m; e índice de massa corporal (IMC) de 22,5±2,0 kg/m2 foram avaliados quanto ao torque (isométrico e excêntrico a 30 e 120o/s) e EMGs dos extensores e flexores do joelho, antes e após 6 semanas de treino isocinético excêntrico (30o/s) dos extensores do joelho.RESULTADOS: O torque extensor do joelho aumentou em todos os modos e velocidades avaliados (P<0,01); a razão I/Q do torque declinou em todas as medidas realizadas (P<0,01), porém a razão I/Q do EMGs manteve-se nos valores pré-treino (P>0,05). As correlações torque/EMGs mostraram-se fracas (r<0.3; P>0,05) para todos os modos de contração, no pré- e pós-treino, porém, houve diferença (P>0,01) na comparação entre o modo excêntrico (30º e 120º/s) e isométrico, pré e pós-treino.CONCLUSÕES: O treino isocinético excêntrico dos extensores do joelho aumentou a diferença na razão I/Q do torque, porém, não alterou a razão I/Q do EMGs, sugerindo que a adaptação pelo aumento do torque associado ao treino excêntrico não alterou o recrutamento das unidades motoras avaliadas pelo EMGs.

The relevance of scapular dysfunction in neck pain: a brief commentary

Synopsis Though our understanding of motor disorders and mechanical neck pain has advanced, the role of scapular dysfunction in mechanical neck pain remains enigmatic. The biomechanical interdependence between the neck and scapula and the potentially deleterious consequences of scapular dysfunction in the cervical region are biomechanically plausible. Yet the relevance of observed scapular dysfunction in patients with neck pain is still inadequately explained by research. However, studies investigating the association between scapular function and neck pain are beginning to emerge. The purpose of this paper was to review the current knowledge of this topic and consider the implications for clinical practice. Level of Evidence Therapy, level 5.

Resistance training and testosterone levels in male patients with chronic kidney disease undergoing dialysis

BACKGROUND

We investigated serum testosterone and insulin-like growth factor 1 (IGF-1) levels' associations with muscle fibre size and resistance training in male dialysis patients.

METHODS

Male patients were included in a 16-week control period followed by 16 weeks of resistance training thrice weekly. Blood samples were obtained to analyse testosterone, luteinizing hormone (LH), IGF-1, and IGF-binding protein 3. Muscle fibres' size was analysed in biopsies from m. vastus lateralis.

RESULTS

The patients' testosterone levels were within the normal range at baseline (n = 20) (19.5 (8.2-52.1) nmol/L versus 17.6 (16.1-18.0), resp.) whereas LH levels were higher (13.0 (5.5-82.8) U/L versus 4.3 (3.3-4.6), P < 0.001, resp.). IGF-1 and IGF-binding protein 3 levels were higher in the patients compared with reference values (203 (59-590) ng/mL versus 151 (128-276), P = 0.014, and 5045 (3370-9370) ng/mL versus 3244 (3020-3983), P < 0.001, resp.). All hormone levels and muscle fibre size (n = 12) remained stable throughout the study. Age-adjusted IGF-1 was associated with type 1 and 2 fibre sizes (P < 0.05).

CONCLUSION

Patients' total testosterone values were normal due to markedly increased LH values, which suggest a compensated primary insufficiency of the testosterone producing Leydig cell. Even though testosterone values were normal, resistance training was not associated with muscle hypertrophy. This trial is registered with ISRCTN72099857.

The increase in surface EMG could be a misleading measure of neural adaptation during the early gains in strength

PURPOSE

To test the validity of using the increase in surface EMG as a measure of neural adaptation during the early gains in strength.

METHODS

Simulation of EMG signals detected by surface bipolar electrode with 20-mm inter-pole distance at different radial distances from the muscle and longitudinal distances from the end-plate area. The increases in the root mean square (RMS) of the EMG signal due to possible alteration in the neural drive or elevation of the intracellular negative after-potentials, detected in fast fatigable muscle fibres during post-tetanic potentiation and assumed to accompany post-activation potentiation, were compared.

RESULTS

Lengthening of the intracellular action potential (IAP) profile due to elevation of the negative after-potentials could affect amplitude characteristics of surface EMG detected at any axial distance stronger than alteration in the neural drive. This was irrespective of the fact that the elevation of IAP negative after-potential was applied to fast fatigable motor units (MUs) only, while changes in frequency of activation (simulating neural drive changes) were applied to all MUs. In deeper muscles, where the fibre-electrode distance was larger, the peripheral effect was more pronounced. The normalization of EMG amplitude characteristics to an M-wave one could result only in partial elimination of peripheral factor influence

CONCLUSIONS

The increase in RMS of surface EMG during the early gains in strength should not be directly related to the changes in the neural drive. The relatively small but long-lasting elevated free resting calcium after high-resistance strength training could result in force potentiation and EMG increase.

Altered Co-contraction of Cervical Muscles in Young Adults with Chronic Neck Pain during Voluntary Neck Motions

[Purpose] Muscle co-contraction is important in stabilizing the spine. The aim of this study was to compare cervical muscle co-contraction in adults with and without chronic neck pain during voluntary movements. [Subjects and Methods] Surface electromyography of three paired cervical muscles was measured in fifteen young healthy subjects and fifteen patients with chronic neck pain. The subjects performed voluntary neck movements in the sagittal and coronal plane at slow speed. The co-contraction ratio was defined as the normalized integration of the antagonistic electromyography activities divided by that of the total muscle activities. [Results] The results showed that the co-contraction ratio of patients was greater during flexion movement, lesser during extension movement, slightly greater during right lateral bending, and slightly lesser during left lateral bending compared with in the controls. [Conclusion] The results suggested that neck pain patients exhibit greater antagonistic muscle activity during flexion and dominate-side bending movements to augment spinal stability, while neuromuscular control provides relatively less protection in the opposite movements. This study helps to specify the changes of the stiffness of the cervical spine in neck pain patients and provides a useful tool and references for clinical assessment of neck disorders.

A promising approach to effectively reduce cramp susceptibility in human muscles: a randomized, controlled clinical trial

BACKGROUND

To investigate if the cramp threshold frequency (CTF) can be altered by electrical muscle stimulation in a shortened position.

METHODS

A total of 15 healthy male sport students were randomly allocated to an intervention (IG, n = 10) and a non-treatment control group (CG, n = 5). Calf muscles of both legs in the IG were stimulated equally twice a week over 6 weeks. The protocol was 3×5 s on, 10 s off, 150 µs impulse width, 30 Hz above the individual CTF, and was at 85% of the maximal tolerated stimulation energy. One leg was stimulated in a shortened position, inducing muscle cramps (CT), while the opposite leg was fixated in a neutral position at the ankle, hindering muscle cramps (nCT). CTF tests were performed prior to the first and 96 h after the 6(th) (3 w) and 12(th) (6 w) training session.

RESULTS

After 3 w, the CTF had significantly (p<0.001) increased in CT calves from 23.3±5.7 Hz to 33.3±6.9 Hz, while it remained unchanged in nCT (pre: 23.6±5.7 Hz, mid: 22.3±3.5 Hz) and in both legs of the CG (pre: 21.8±3.2 Hz, mid: 22.0±2.7 Hz). Only CT saw further insignificant increases in the CTF. The applied stimulation energy (mA² • µs) positively correlated with the effect on the CTF (r = 0.92; p<0.001).

CONCLUSIONS

The present study may be useful for developing new non-pharmacological strategies to reduce cramp susceptibility.

TRIAL REGISTRY

German Clinical Trials Register DRKS00005312.

Implications of movement-related cortical potential for understanding neural adaptations in muscle strength tasks

This systematic review aims to provide information about the implications of the movement-related cortical potential (MRCP) in acute and chronic responses to the counter resistance training. The structuring of the methods of this study followed the proposals of the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses). It was performed an electronically search in Pubmed/Medline and ISI Web of Knowledge data bases, from 1987 to 2013, besides the manual search in the selected references. The following terms were used: Bereitschaftspotential, MRCP, strength and force. The logical operator “AND” was used to combine descriptors and terms used to search publications. At the end, 11 studies attended all the eligibility criteria and the results demonstrated that the behavior of MRCP is altered because of different factors such as: force level, rate of force development, fatigue induced by exercise, and the specific phase of muscular action, leading to an increase in the amplitude in eccentric actions compared to concentric actions, in acute effects. The long-term adaptations demonstrated that the counter resistance training provokes an attenuation in the amplitude in areas related to the movement, which may be caused by neural adaptation occurred in the motor cortex.

A longitudinal study of knee pain in older men: Concord Health and Ageing in Men Project

BACKGROUND

chronic knee pain is still considered a fairly benign disease by many, an 'unavoidable' consequence of ageing. This passive acceptance may be unnecessarily exposing older people to disability and serious co-morbidity. The aim of this study was to determine the disease burden associated with chronic knee pain and the role of knee extensor strength as a modifiable risk factor.

METHODS

a longitudinal cohort study with 2-year follow-up conducted among 1,587 community-dwelling men aged 70 years and over, 637 (40%) reported chronic knee pain. Of the 950 (60%) men without knee pain at baseline, 768 (81%) returned for the follow-up assessment with 150 (20%) reporting incident chronic knee pain.

RESULTS

knee pain was significantly associated with marked mobility disability [odds ratio (OR) 2.38; 95% confidence interval (CI) 1.74-3.29], falls (OR: 1.31; 95% CI: 1.01-1.70) and having four or more co-morbidity (OR: 1.63; 95% CI: 1.16-2.30) as well as reduced knee extensor strength and mass (dual X-ray absorptiometry). Men with incident knee pain at the 2-year follow-up assessment demonstrated greater increases in these measures of disease burden and greater decreases in muscle strength and mass, compared with those without incident chronic knee pain. Obesity, high co-morbidity burden, back pain, higher levels of physical activity or low knee extensor strength were all significant risk factors for incident knee pain.

CONCLUSION

prevention of chronic knee pain may reduce a considerable burden of mobility disability and increased risk of serious co-morbidity among older men.

Neuromuscular and metabolic responses to three different resistance exercise methods

PURPOSE

The aim of this study was to compare the effect of resistance exercise with three different methods on integrated electromyography (IEMG) and metabolic responses in recreational athletes.

METHODS

Twenty four males (mean 23.59±0.87 years) were randomly assigned to three experimental groups. Participants performed knee extension exercises: Slow (SL: 3-3, 3s for each concentric and eccentric action with 50% of 1 RM), Normal (NH: 1-1, 1 s for each concentric and eccentric action 80% of 1 RM) and Traditional (TH: 2-4, 2s for concentric and 4s for eccentric action with 80% of 1 RM). Plasma lactate, glucose and triglyceride concentration and IEMG was measured before and immediately after performing four sets of resistance exercise.

RESULTS

Each method significantly decreased IEMG (P<0.05), but there was no significant difference between groups. Lactate was increased following TH and NH more than SL method (P<0.05). Each method significantly increased plasma glucose (P<0.05). Work considering time under tension (workTUT) was higher (P<0.05) during TH method than the other methods and during SL it was higher than NH method (P<0.05). Volume load was higher (P<0.05) during NH than the other two methods and during TH it was higher than SL method (P<0.05).

CONCLUSION

These results indicate that exercise intensity during the resistance exercise is important for the enhancement of lactate responses, but the slow resistance exercise method could induce acute neuromuscular response as much as high intensity methods. It seems that this method will be advantageous for those who want to increase acute neuromuscular changes with low exercise intensity and volume.

Preoperative strength training for elderly patients awaiting total knee arthroplasty

Objective. To investigate the feasibility and effects of additional preoperative high intensity strength training for patients awaiting total knee arthroplasty (TKA). Design. Clinical controlled trial. Patients. Twenty-two patients awaiting TKA. Methods. Patients were allocated to a standard training group or a group receiving standard training with additional progressive strength training for 6 weeks. Isometric knee extensor strength, voluntary activation, chair stand, 6-minute walk test (6MWT), and stair climbing were assessed before and after 6 weeks of training and 6 and 12 weeks after TKA. Results. For 3 of the 11 patients in the intensive strength group, training load had to be adjusted because of pain. For both groups combined, improvements in chair stand and 6MWT were observed before surgery, but intensive strength training was not more effective than standard training. Voluntary activation did not change before and after surgery, and postoperative recovery was not different between groups (P > 0.05). Knee extensor strength of the affected leg before surgery was significantly associated with 6-minute walk (r = 0.50) and the stair climb (r - = 0.58, P < 0.05). Conclusion. Intensive strength training was feasible for the majority of patients, but there were no indications that it is more effective than standard training to increase preoperative physical performance. This trial was registered with NTR2278.

Inter-subject variability of muscle synergies during bench press in power lifters and untrained individuals

The purpose of the study was to elucidate the role of expertise on muscle synergies involved in bench press. Ten expert power lifters (EXP) and nine untrained participants (UNT) completed three sets of eight repetitions at 60% of three repetition maximum in bench press. Muscle synergies were extracted from surface electromyography data of 21 bench press cycles using non-negative matrix factorization algorithm. The synergy activation coefficient represents the relative contribution of the muscle synergy to the overall muscle activity pattern, while the muscle synergy vector represents the relative weighting of each muscle within each synergy. Describing more than 90% of the variability, two muscle synergies reflected the eccentric and concentric phase. The cross-correlations (ρ(max)) for synergy activation coefficient 2 (concentric phase) were 0.83 [0.71;0.88] and 0.59 [0.49;0.77] [Median ρ(max) (25th;75th percentile)] (P = 0.001) in UNT and EXP, respectively. Median correlation coefficient (ρ) for muscle synergy vector 2 was 0.15 [-0.08;0.46] and 0.48 [0.02;0.70] (P = 0.03) in UNT and EXP, respectively. Thus, EXP showed larger inter-subject variability than UNT in the synergy activation coefficient during the concentric phase, while the muscle synergy vectors were less variable in EXP. This points at the importance of a specialized neural strategy in elite bench press performance.

Molecular mechanisms of muscle plasticity with exercise

The skeletal muscle phenotype is subject to considerable malleability depending on use. Low-intensity endurance type exercise leads to qualitative changes of muscle tissue characterized mainly by an increase in structures supporting oxygen delivery and consumption. High-load strength-type exercise leads to growth of muscle fibers dominated by an increase in contractile proteins. In low-intensity exercise, stress-induced signaling leads to transcriptional upregulation of a multitude of genes with Ca(2+) signaling and the energy status of the muscle cells sensed through AMPK being major input determinants. Several parallel signaling pathways converge on the transcriptional co-activator PGC-1α, perceived as being the coordinator of much of the transcriptional and posttranscriptional processes. High-load training is dominated by a translational upregulation controlled by mTOR mainly influenced by an insulin/growth factor-dependent signaling cascade as well as mechanical and nutritional cues. Exercise-induced muscle growth is further supported by DNA recruitment through activation and incorporation of satellite cells. Crucial nodes of strength and endurance exercise signaling networks are shared making these training modes interdependent. Robustness of exercise-related signaling is the consequence of signaling being multiple parallel with feed-back and feed-forward control over single and multiple signaling levels. We currently have a good descriptive understanding of the molecular mechanisms controlling muscle phenotypic plasticity. We lack understanding of the precise interactions among partners of signaling networks and accordingly models to predict signaling outcome of entire networks. A major current challenge is to verify and apply available knowledge gained in model systems to predict human phenotypic plasticity.

Aerobic exercise training increases neuronal nitric oxide release and bioavailability and decreases noradrenaline release in mesenteric artery from spontaneously hypertensive rats

OBJECTIVE

To study the effect of aerobic exercise training on sympathetic, nitrergic and sensory innervation function in superior mesenteric artery from spontaneously hypertensive rats (SHRs).

METHODS

De-endothelized vascular rings from sedentary and trained SHRs (treadmill 12 weeks) were used. Vasomotor responses to electrical field stimulation (EFS), noradrenaline, nitric oxide donor DEA-NO and calcitonin gene-related peptide (CGRP) were studied. Neuronal nitric oxide synthase (nNOS) expression and nitric oxide, superoxide anions (O(2.-)), noradrenaline and CGRP levels were also determined.

RESULTS

Aerobic exercise training decreased vasoconstrictor response to EFS but increased noradrenaline response. Phentolamine decreased while N(ω)-nitro-(L)-arginine methyl ester ((L)-NAME) increased the response to EFS; the effect of both drugs was greater in trained animals. Training also decreased noradrenaline release and O(2.-) production and increased nNOS expression, nitric oxide release and the vasodilator response to DEA-NO. The O(2.-) scavenger tempol increased DEA-NO-induced vasodilation only in sedentary rats. The EFS-induced contraction was increased to a similar extent in both experimental groups by preincubation with CGRP (8-37). CGRP release and vasodilator response were not modified by training.

CONCLUSION

Aerobic exercise training decreases contractile response to EFS in mesenteric artery from SHRs. This effect is the net result of decreased noradrenaline release, increased sensitivity to the vasoconstrictive effects of noradrenaline and increased neuronal nitric oxide release and bioavailability. These modifications might contribute to the beneficial effects of aerobic exercise training on blood pressure.

Eletromiografia do bíceps braquial em contrações dinâmicas

INTRODUÇÃO: A reprodutibilidade da atividade eletromiográfica de superfície (EMG) é mais estudada em protocolos que envolvem contrações isométricas. Alguns fatores relacionados às contrações dinâmicas podem contribuir para a instabilidade do sinal mioelétrico e dificultar a reprodutibilidade da medida da EMG. OBJETIVO: Determinar a reprodutibilidade teste-reteste e quantificar o erro técnico da medida da frequência mediana (FM) e da amplitude (root mean square, RMS) da EMG, em contrações dinâmicas e estáticas. MÉTODOS: Dez sujeitos foram testados em dois dias, sendo a atividade EMG registrada na maior porção do bíceps braquial. No primeiro dia foi feito o teste de uma repetição máxima (1RM) e de contração voluntária máxima (CVM). No segundo dia foram realizadas duas séries de 10 contrações dos flexores do cotovelo com 75% de 1RM, entremeadas por 1 h em repouso. Antes de cada série foi realizada uma CVM. RESULTADOS: Para a FM e RMS foi observado alto coeficiente de correlação intraclasse para o sinal do bíceps braquial (CCI = 0,90-0,98 para a FM; CCI = 0,89-0,94 para o RMS) e de baixo para moderado coeficiente de variação (CV = 2,5-6,2% para a FM; CV = 14,6-16,3% para o RMS) em ambos os testes. Não foi observada diferença significativa entre teste e reteste (p > 0,05). CONCLUSÃO: A FM e o RMS apresentam alta confiabilidade e baixo a moderado erro em contrações estáticas e dinâmicas, possibilitando o uso da EMG para investigação da fadiga e de desordens neuromusculares.

Exercise training improves aerobic capacity, muscle strength, and quality of life in renal transplant recipients

Renal transplant recipients (RTR) have reduced peak aerobic capacity, muscle strength, arterial function and an unfavorable cardiovascular disease risk (CVD) profile. This study compared the effects of 12 weeks of supervised endurance and strength training (EST, n = 16) versus usual care (UC, n = 15) on peak aerobic capicity, cardiovascular and skeletal muscle function, CVD risk profile, and quality of life (QOL) in RTR (55 ± 13 years). Peak aerobic capacity and exercise hemodynamics, arterial compliance, 24-h blood pressure, muscle strength, lean body mass, CVD risk score, and QOL were assessed before and after 12 weeks. The change in peak aerobic capacity (EST: 2.6 ± 3.1 vs. UC: -0.5 ± 2.5 mL/(kg·min)), cardiac output (EST: 1.7 ± 2.6 vs. UC: -0.01 ± 0.8 L/min), leg press (EST: 48.7 ± 34.1 vs. UC: -10.5 ± 37.7 kg) and leg extension strength (EST: 9.5 ± 10.3 vs. UC: 0.65 ± 5.5 kg) improved significantly after EST compared with UC. The overall change in QOL improved significantly after 12 weeks of EST compared with UC. No significant difference was found between groups for lean body mass, arterial compliance, 24-h blood pressure or CVD risk score. Supervised EST is an effective intervention to improve peak exercise aerobic capacity and cardiac output, muscle strength and QOL in clinically stable RTR.

Sensibilidade e especificidade do diagnóstico de desempenho da força por diferentes testes de saltos verticais em futebolistas e voleibolistas na puberdade

OBJETIVO: Avaliar a sensibilidade e a especificidade de diferentes protocolos de medida dos testes de saltos verticais para o diagnóstico da força explosiva em futebolistas e voleibolistas na puberdade. MÉTODOS: Estudo transversal com população não probabilística de 110 jovens atletas do sexo masculino (60 futebolistas e 50 voleibolistas) na faixa etária de 13 a 18 anos pertencentes a clubes da região metropolitana de Campinas, SP, Brasil. Os participantes tiveram sua maturação biológica avaliada por dois métodos: autoavaliação e medida clínica. Após essa avaliação, foram incluídos os classificados como púberes (25 futebolistas e 23 voleibolistas). Foram coletados dados antropométricos (massa corporal, estatura e dobras cutâneas) e testes de saltos verticais: squat jump (SJ), counter movement jump (CMJ), drop jump (DJ; 40 cm height) e saltos verticais contínuos com cinco segundos de duração (CJ5s). Foram calculadas as medidas de desempenho diagnóstico: sensibilidade, especificidade e acurácia. O nível de significância adotado foi 5% para todos os testes. RESULTADOS: As forças explosivas estimadas pelos métodos de SJ e CMJ apresentaram sensibilidades equivalentes, enquanto o SJ apresentou maior especificidade do que os três métodos, e a acurácia do SJ foi diferente dos outros métodos, a qual foi alta (superior a 80%). CONCLUSÃO: O diagnóstico da força explosiva como teste SJ apresentou sensibilidade e especificidade elevadas, com seu valor preditivo alto na puberdade.

Fatigue in healthy and diseased individuals

OBJECTIVES

Although fatigue is experienced by everyone, its definition and classification remains under debate.

METHODS

A review of the previously published data on fatigue.

RESULTS

Fatigue is influenced by age, gender, physical condition, type of food, latency to last meal, mental status, psychological conditions, personality type, life experience, and the health status of an individual. Fatigue may not only be a symptom but also a measurable and quantifiable dimension, also known as fatigability. Additionally, it may be classified as a condition occurring at rest or under exercise or stress, as physiologic reaction or pathologic condition, as spontaneous phenomenon or triggerable state, as resistant or irresistant to preconditioning, training, or attitude, as prominent or collateral experience, and as accessible or inaccessible to any type of treatment or intervention. Fatigue may be the sole symptom of a disease or one among others. It may be also classified as acute or chronic. Quantification of fatigability is achievable by fatigue scores, force measurement, electromyography, or other means. Fatigue and fatigability need to be delineated from conditions such as sleepiness, apathy, exhaustion, exercise intolerance, lack of vigor, weakness, inertia, or tiredness. Among neurological disorders, the prevalence of fatigue is particularly increased in multiple sclerosis, amyotrophic lateral sclerosis, Parkinson disease, traumatic brain injury, stroke, and bleeding and also in neuromuscular disorders. Fatigue may be influenced by training, mental preconditioning, or drugs.

CONCLUSIONS

Fatigue needs to be recognized as an important condition that is not only a symptom but may also be quantified and can be modified by various measures depending on the underlying cause.

Should we think about wrist extensor after flexor tendon repair?

OBJECTIVE

To evaluate the activity of wrist extensor muscle, correlating with wrist motion during gripping after flexor tendon repair.

DESIGN

Cross-sectional clinical measurement study.

SETTING

Laboratory for biomechanics and rehabilitation.

SUBJECTS

A total of 11 patients submitted to rehabilitation by early passive motion of the fingers with wrist flexion position were evaluated after 8 weeks of fingers flexor tendon repair and 11 healthy volunteers, all ranging from 20 to 37 years of age.

INTERVENTION

Volunteers performed an isometric standardized gripping task.

MAIN MEASURES

We used electrogoniometry to analyze wrist range of motion and surface electromyography, considering 100% maximum voluntary contraction to represent the amplitude of electromyographic activity of the extensor carpi radialis and flexor digitorum superficialis.

RESULTS

Patients with flexor tendon repair showed co-activation deficit between wrist extensor (extensor carpi radialis) and flexor finger muscles (flexor digitorum superficialis) during gripping in the intermediate phase of rehabilitation, despite some recovering mobility for wrist extension (p ≤ 0.05). A moderate correlation between range of motion and extensor carpi radialis was present only for injured group (r = 0.32). Total active motion score, which represents finger active excursion, was regular or poor in 65% of cases, all with nerve repair associated.

CONCLUSION

Wrist extensors have an important synergist role at handgrip, although some imbalance can be present after flexor tendon repair. These preliminary findings suggest that emphasis could be directed to add synergistic wrist motion in rehabilitation protocols after flexor tendon repair. Future studies with early active rehabilitation are necessary.

Evaluation of sigmoidal maturation and allometric models: prediction of propofol clearance in neonates and infants

The main objectives of this report are to predict propofol clearance in neonates and infants by a maturation model that includes age and weight and to compare the predictive performance of propofol maturation model with a simple allometric model (clearance vs. body weight). Age, weight, and propofol clearance data were obtained from the literature. A maturation model for propofol was developed using data from neonates, toddlers, children, adolescents, and adults (N = 71). The allometric model was developed using the same data as the maturation model. The predicted clearance of propofol in an individual neonate or infant from these models was compared with the observed clearance (16 neonates and 22 infants) in that individual neonate or infant. The prediction of propofol clearance in most of the individual neonates or infants by both maturation and allometric models was poor. However, the mean predicted propofol clearance in the neonates by both models was comparable with the observed clearance, but the mean predicted propofol clearance in the infants was underpredicted by both models. The propofol maturation and simple allometric model performed poorly for the prediction of propofol clearance in individual neonate and infant.

Central Factors Explain Muscle Weakness in Young Fallers With Parkinson’s Disease

Background. Muscle weakness in old Parkinson’s disease (PD) patients has been shown to impair their mobility, although the specific origin of this weakness and its relation to falls has not been well examined in young patients. Objective. This study aimed to analyze the possible contribution of central factors to muscle weakness of the triceps surae and quadriceps femoris muscles in young faller and nonfaller PD patients. Methods. Twenty-six young PD patients (fallers, n = 13 and nonfallers, n = 13) and 15 matched healthy controls performed several isometric maximal voluntary knee extension and plantar flexion contractions (MVC) of the most affected leg on a dynamometer. We estimated the maximal resultant agonist moments, the antagonistic moment of hamstrings and tibialis anterior during MVCs and the activation deficit of the quadriceps femoris and triceps surae muscles. Results. Only the Parkinson fallers showed significantly lower muscle strength, higher antagonistic moments and higher activation deficit compared with controls. Multiple regression analysis showed that the antagonistic moments and the activation deficit explained about 39% and 27%, of the variance in the maximal resultant moments of the knee extensors and the plantar flexors, respectively. Conclusions. Our findings suggest that Parkinson fallers are affected by strength impairments arising from the central nervous system and not from the peripheral muscle contractile capacity, even at early stages of the disease and young age. High-intensity resistance training may help enhance neural drive and decrease unwanted antagonistic moments and reduce the risk of falls.

Sports and exercise-related tendinopathies: a review of selected topical issues by participants of the second International Scientific Tendinopathy Symposium (ISTS) Vancouver 2012

In September 2010, the first International Scientific Tendinopathy Symposium (ISTS) was held in Umeå, Sweden, to establish a forum for original scientific and clinical insights in this growing field of clinical research and practice. The second ISTS was organised by the same group and held in Vancouver, Canada, in September 2012. This symposium was preceded by a round-table meeting in which the participants engaged in focused discussions, resulting in the following overview of tendinopathy clinical and research issues. This paper is a narrative review and summary developed during and after the second ISTS. The document is designed to highlight some key issues raised at ISTS 2012, and to integrate them into a shared conceptual framework. It should be considered an update and a signposting document rather than a comprehensive review. The document is developed for use by physiotherapists, physicians, athletic trainers, massage therapists and other health professionals as well as team coaches and strength/conditioning managers involved in care of sportspeople or workers with tendinopathy.

Effects of a low-volume, vigorous intensity step exercise program on functional mobility in middle-aged adults

Aging-related decline in functional mobility is associated with loss of independence. This decline may be mitigated through programs of physical activity. Despite reports of aging-related mobility impairment in middle-aged adults, this age group has been largely overlooked in terms of exercise programs that target functional mobility and the preservation of independence in older age. A method to quantitatively assess changes in functional mobility could direct rehabilitation in a proactive rather than reactive manner. Thirty-three healthy but sedentary middle-aged adults participated in a four week low-volume, vigorous intensity stepping exercise program. Two baseline testing sessions and one post-training testing session were conducted. Functional mobility was assessed using the timed up and go (TUG) test, with its constituent sit-to-walk and walk-to-sit phases examined using a novel inertial sensor-based method. Additionally, semi-tandem balance and knee extensor muscle isometric torque were assessed. Trunk acceleration during walk-to-sit reduced significantly post-training, suggesting altered movement control due to the exercise program. No significant training-induced changes in sit-to-walk acceleration, TUG time, balance or torque were observed. The novel method of functional mobility assessment presented provides a reliable means to quantify subtle changes in mobility during postural transitions. Over time, this exercise program may improve functional mobility.

Efeito do uso profilático do anti-inflamatório não-esteroide ibuprofeno sobre o desempenho em uma sessão de treino de força

INTRODUÇÃO: Medicamentos anti-inflamatórios não esteroides, como o ibuprofeno, têm sido utilizados por atletas de várias modalidades com o intuito de aumentar desempenho esportivo. OBJETIVO: Verificar o efeito do uso profilático de ibuprofeno sobre desempenho em uma sessão de treino de força. MÉTODOS: Um ensaio clínico, cruzado, randomizado, duplo-cego e placebo-controlado foi desenvolvido com 12 praticantes regulares de treino de força do sexo masculino, os quais realizaram uma sessão de treino após a ingestão de ibuprofeno (1,2 g) e uma outra após a ingestão de placebo. Seis séries dos exercícios supino e agachamento foram realizadas em cada sessão de treino com uma carga constante correspondente a 65% da 1RM de cada exercício. O desempenho no treinamento foi mensurado através do número de repetições que os voluntários conseguiram realizar em cada série de exercício a cada sessão de treino de força. RESULTADOS: Não foram verificadas diferenças significativas de desempenho no treino de força com a administração prévia de placebo ou ibuprofeno (p > 0,05). CONCLUSÃO: A ingestão de ibuprofeno nos parâmetros de administração adotados pelo presente estudo não promove qualquer tipo de alteração na tolerância ao exercício em uma sessão isolada de treino de força, o que contraria a indicação dessa substância para fins ergogênicos no treino de força.

Peculiarities of extracellular potentials produced by deep muscles. Part 2: motor unit potentials

The potential fields generated by single fibres far from the sources are non-propagating. This suggests that there should be differences in the features of surface motor unit (MU) potentials (MUPs) detected from deep and superficial muscles. We explored the features using a simulation approach. We have shown that the non-propagating character and similar shapes among surface MUPs recorded over a wide area above deep muscles with monopolar or longitudinal single differential (LSD) electrodes are natural. Contrary to close distances, at large radial distances single differentiation did not emphasize MUP main phase relative weight. The position of the end plate area could be estimated with LSD detections only for MUs with long (123 mm) almost symmetric fibres. With short fibres, the LSD main phase was masked by the outlined terminal phases. This could be misleading in MUP analysis since the terminal phases reflect standing sources. The highly asymmetric fibres could yield peculiar MUP shapes resembling MUPs of two distinct MUs. We have shown that the relative weight of terminal phases at large fibre-electrode distance decreases under abnormal peripheral conditions. However, the changes in membrane depolarization due to fatigue or pathology could be assessed non-invasively also from deep muscles.

Explosive sport training and torque kinetics in children

A high rate of force development (RFD) is often more important than maximal force in daily and sports activities. In children, resistance training has been shown to increase maximal force. It is unclear whether, or to what extent, can children improve RFD and force kinetics. For this study, we compared strength and force kinetics of boy gymnasts with those of untrained boys and untrained men. Eight boy gymnasts (age, 9.5 ± 1.2 y), 20 untrained boys (age, 10.1 ± 1.3 y), and 20 untrained men (age, 22.9 ± 4.4 y) performed maximal, explosive, isometric elbow flexions (EF) and knee flexions (KF). Peak torque (maximal voluntary contraction (MVC)), elapsed times to 10%-100% MVC, peak rate of torque development (RTDpk), and other kinetics parameters were determined. When gymnasts were compared with untrained boys, size-normalized EF MVC was 11%-20% higher, RTDpk was 32% higher, and times to 30% and 80% MVC were 16% and 55% shorter, respectively (p < 0.05). No corresponding differences were observed in KF. Furthermore, although the normalized EF MVC was 28% lower in gymnasts than in men (p < 0.001), their torque kinetics parameters were similar. These findings highlight the specificity of gymnastics training, which markedly elevated the torque kinetics of young, prepubertal boys to adult levels, but only moderately affected peak torque. It is suggested that neurologic adaptations, such as enhanced firing and activation rates or increased type II motor-unit recruitment, as well as changes in musculotendinous stiffness, could explain these findings.

Factors relating to gender specificity of unloading-induced declines in strength

INTRODUCTION

This investigation aimed to: (1) confirm whether women were more vulnerable to the negative neuromuscular adaptations elicited by muscle unloading and if so, (2) determine which physiological mechanism(s) explain those gender-related differences.

METHODS

Healthy young men (20.7 ± 0.3 years) and women (20.3 ± 0.3 years)-(N = 12/group)-participated by completing neuromuscular functional tests before and after 7 days of unloading.

RESULTS

During isokinetic testing of peak torque, work performed, and power, women displayed significantly (P ≤ 0.05) greater declines in performance than men at 1.05 and 2.09, but not 0.53 rads/s. During maximal isometric contractions, women experienced greater strength decrements. Similar gender-specific adaptations to unloading were found in EMG activity, but not muscle mass, neuromuscular transmission, or force relative to EMG.

CONCLUSIONS

Women are more susceptible to the adaptations of muscle unloading, and disturbances in neural drive from the central nervous system are probably responsible.

Fast changes in direction during human locomotion are executed by impulsive activation of motor modules

This study investigated the modular control of complex locomotor tasks that require fast changes in direction, i.e., cutting manoeuvres. It was hypothesized that such tasks are accomplished by an impulsive (burst-like) activation of a few motor modules, as observed during walking and running. It was further hypothesized that the performance in cutting manoeuvres would be associated to the relative timing of the activation impulses. Twenty-two healthy men performed 90° side-step cutting manoeuvres while electromyography (EMG) activity from 16 muscles of the supporting limb and trunk, kinematics, and ground reaction forces were recorded. Motor modules and their respective temporal activations were extracted from the EMG signals by non-negative matrix factorization. The kinematic analysis provided the velocity of the centre of mass and the external work absorbed during the load acceptance (negative work, external work during absorption (W-Abs)) and propulsion phases (positive work, external work during propulsion (W-Prp)) of the cutting manoeuvres. Five motor modules explained the EMG activity of all muscles and were driven in an impulsive way, with timing related to the initial contact (M2), load acceptance (M3), and propulsion (M4). The variability in timing between impulses across subjects was greater for cutting manoeuvres than for running. The timing difference between M2 and M3 in the cutting manoeuvres was significantly associated to W-Abs (r(2)=0.45) whereas the timing between M3 and M4 was associated to W-Prp (r(2)=0.43). These results suggest that complex locomotor tasks can be achieved by impulsive activation of muscle groups, and that performance is associated to the specific timing of the activation impulses.

Strength training reduces intracortical inhibition

AIM

Paired-pulse transcranial magnetic stimulation was used to investigate the influence of 4 weeks of heavy load squat strength training on corticospinal excitability and short-interval intracortical inhibition (rectus femoris muscle).

METHODS

Participants (n = 12) were randomly allocated to a strength training or control group. The strength training group completed 4 weeks of heavy load squat strength training. Recruitment curves were constructed to determine values for the slope of the curve, V50 and peak height. Short-interval intracortical inhibition was assessed using a subthreshold (0.7 × active motor threshold) conditioning stimulus, followed 3 ms later by a supra-threshold (1.2 × active motor threshold) test stimulus. All motor evoked responses were taken during 10% of maximal voluntary isometric contraction (MVC) torque and normalized to the maximal M-wave.

RESULTS

The strength training group attained 87% increases in 1RM squat strength (P < 0.01), significant increases in measures of corticospinal excitability (1.2 × Motor threshold: 116%, P = 0.016; peak height of recruitment curve = 105%, P < 0.001), and a 32% reduction in short-interval intracortical inhibition (P < 0.01) following the 4-week intervention compared with control. There were no changes in any dependent variable (P > 0.05) detected in the control group.

CONCLUSION

Repeated high force voluntary muscle activation in the form of short-term strength training reduces short-interval intracortical inhibition. This is consistent with studies involving skilled/complex tasks or novel movement patterns and acute studies investigating acute voluntary contractions.