Changes in three dimensional lumbo-pelvic kinematics and trunk muscle activity with speed and mode of locomotion

Background Control of the trunk is critical for locomotor efficiency. However, investigations of trunk muscle activity and three-dimensional lumbo-pelvic kinematics during walking and running remain scarce. Methods. Gait parameters and three-dimensional lumbo-pelvic kinematics were recorded in seven subjects. Electromyography recordings of abdominal and paraspinal muscles were made using fine-wire and surface electrodes as subjects walked on a treadmill at 1 and 2 ms(-1) and ran at 2, 3, 4 and 5 ms(-1). Findings. Kinematic data indicate that the amplitude but not timing of lumbo-pelvic motion changes with locomotor speed. Conversely, a change in locomotor mode is associated with temporal but not spatial adaptation in neuromotor strategy. That is, peak transverse plane lumbo-pelvic rotation occurs at foot strike during walking but prior to foot strike during running. Despite this temporal change, there is a strong correlation between the amplitude of transverse plane lumbo-pelvic rotation and stride length during walking and running. In addition, Jumbo-pelvic motion was asymmetrical during all locomotor tasks. Trunk muscle electromyography occurred biphasically in association with foot strike. Transversus abdominis was tonically active with biphasic modulation. Consistent with the kinematic data, electromyography activity of the abdominal muscles and the superficial fibres of multifidus increased with locomotor speed, and timing of peak activity of superficial multifidus and obliquus externus abdominis was modified in association with the temporal adaptation in lumbo-pelvic motion with changes in locomotor mode. Interpretation. These data provide evidence of the association between lumbo-pelvic motion and trunk muscle activity during locomotion at different speeds and modes. (c) 2005 Elsevier Ltd. All rights reserved.

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.

Improved physical performance in older adults undertaking a short-term programme of high-velocity resistance training

Background: The age-related loss of muscle power in older adults is greater than that of muscle strength and is associated with a decline in physical performance. Objective: To investigate the effects of a short-term high-velocity varied resistance training programme on physical performance in healthy community-dwelling adults aged 60-80 years. Methods: Subjects undertook exercise (EX; n = 15) or maintained customary activity (controls, CON; n = 10) for 8 weeks. The EX group trained 2 days/week using machine weights for three sets of eight repetitions at 35, 55, and 75% of their one-repetition maximum (the maximal weight that an individual can lift once with acceptable form) for seven upper- and lower-body exercises using explosive concentric movements. Results: Fourteen EX and 10 CON subjects completed the study. Dynamic muscle strength significantly increased (p = 0.001) in the EX group for all exercises (from 21.4 +/- 9.6 to 82.0 +/- 59.2%, mean +/- SD) following training, as did knee extension power (p < 0.01). Significant improvement occurred for the EX group in the floor rise to standing (10.4 &PLUSMN; 11.5%, p = 0.004), usual 6-metre walk (6.6 &PLUSMN; 8.2%, p = 0.010), repeated chair rise (10.4 &PLUSMN; 15.6%, p = 0.013), and lift and reach (25.6 &PLUSMN; 12.1%, p = 0.002) performance tasks but not in the CON group. Conclusions: Progressive resistance training that incorporates rapid rate-of-force development movements may be safely undertaken in healthy older adults and results in significant gains in muscle strength, muscle power, and physical performance. Such improvements could prolong functional independence and improve the quality of life. Copyright (C) 2005 S. Karger AG, Basel.

Resistance training for the older adult: Manipulating training variables to enhance muscle strength

Resistance training has been shown to reliably and substantially enhance muscle function in older adults and these improvements can be accompanied by improved functional performance. Training variables should be manipulated to enhance muscle strength and minimize injury risks in this population.

An endurance-strength training regime is effective in reducing myoelectric manifestations of cervical flexor muscle fatigue in females with chronic neck pain

Objective: The purpose of this study was to investigate whether an endurance-strength training program is effective in reducing myoelectric manifestations of sternocleidomastoid (SCM) and anterior scalene (AS) muscle fatigue which have been found to be greater in people with chronic neck pain. Methods: Fifty-eight female patients with chronic non-severe neck pain were randomized into one of two 6-week exercise intervention groups: an endurance-strength training regime for the cervical flexor muscles or a referent exercise intervention involving low load retraining of the cranio-cervical flexor muscles. The primary outcomes were a change in maximum voluntary contraction (MVC) force and change of the initial value and rate of change of the mean frequency, average rectified value and conduction velocity detected from the SCM and AS muscles during sub-maximal isometric cervical flexion contractions at 50, 25 and 10% MVC. Results: At the 7th week follow-up assessment, the endurance-strength training group revealed a significant increase in MVC force and a reduction in the estimates of the initial value and rate of change of the mean frequency for both the SCM and AS muscles (P < 0.05). Both exercise groups reported a reduced average intensity of neck pain and reduced neck disability index score (P < 0.05). Conclusions: An endurance-strength exercise regime for the cervical flexor muscles is effective in reducing myoelectric manifestations of superficial cervical flexor muscle fatigue as well as increasing cervical flexion strength in a group of patients with chronic non-severe neck pain. Significance: Provision of load to challenge the neck flexor muscles is required to reduce the fatigability of the SCM and AS muscles in people with neck pain. Improvements in cervical muscle strength and reduced fatigability may be responsible for the reported efficacy with this type of exercise program. (c) 2006 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All fights reserved.

High- and low-volume resistance training similarly enhances functional performance in older adults

It is well known that resistance training improves muscle strength in older adults and may enhance or preserve functional performance. However, it is unclear if the volume of work undertaken in the elderly alters the response in functional performance. PURPOSE: To investigate the effect of a high- versus low-volume resistance training program on functional performance in older adults. METHODS: Thirty-two healthy men and women aged 65-78 years were randomly assigned to either a single-set (SS, n = 16) or 3-set (MS, n = 16) progressive resistance training program for 20 weeks. Groups trained 2 days per week using machine weights at 8 repetitions maximum (8-RM) for 7 upper and lower body exercises. Muscle strength was assessed by the 1-RM and functional performance by a battery of tests (repeated chair rise, usual and fast 6-m walk, 6-m backwards walk, floor rise to standing, stair climb, and 400-m walk time). RESULTS: Twenty-eight subjects completed the study. There was no difference between groups at baseline in muscle strength or functional performance. Whole body muscle strength significantly increased in both groups with greater gains in the 3-set group (MS 32.9 ± 3.1%; SS 18.6 ± 2.7%, mean ± SE; P < 0.01). Significant improvement (time effect, P < 0.01) occurred for both groups in the chair rise (MS 13.6 ± 3.2%; SS 10.2 ± 3.0%), 6-m backwards walk (MS 14.9 ± 3.3%; SS 14.3 ± 4.2%), stair climb (MS 6.4 ± 2.8%; SS 7.7 ± 3.1%) and 400-m walk (MS 7.4 ± 1.4%; SS 3.9 ± 1.2%). There were no interaction (group × time) effects for functional performance and no differences by sex. CONCLUSION: Resistance training that utilizes either a singleset or 3-set regimen may significantly and similarly improve functional performance in community-dwelling older adults. Enhancement of functional performance may prolong independence and improve quality of life. ©2004The American College of Sports Medicine

Adaptation of motor control to training and disuse : contribution of muscle synergy analysis and movement variability

The well-known degrees of freedom problem originally introduced by Nikolai Bernstein (1967) results from the high abundance of degrees of freedom in the musculoskeletal system. Such abundance in motor control have two sides: i) because it is unlikely that the Central Nervous System controls each degree of freedom independently, the complexity of the control needs to be reduced, and ii) because there are many options to perform a movement, a repetition of a given movement is never the same. It leads to two main topics in motor control and biomechanics: motor coordination and motor variability. The present thesis aimed to understand how motor systems behave and adapt under specific conditions. This thesis comprises three studies that focused on three topics of major interest in the field of sports sciences and medicine: expertise, injury risk and fatigue. The first study (expertise) has focused on the muscle coordination topic to further investigate the effect of expertise on the muscle synergistic organization, which ultimately may represent the underlying neural strategies. Studies 2 (excessive medial knee displacement) and 3 (fatigue) both aimed to better understand its impact on the dynamic local stability. The main findings of the present thesis suggest: 1) there is a great robustness in muscle synergistic organization between swimmers at different levels of expertise (study 1, chapter II), which ultimately indicate that differences in muscle coordination is mainly explained by peripheral adaptations; 2) injury risk factors such as excessive medial knee displacement (study 2, chapter III) and fatigue (study 3, chapter IV) alter the dynamic local stability of the neuromuscular system towards a more unstable state. This change in dynamic local stability represents a loss of adaptability in the neuromuscular system reducing the flexibility to adapt to a perturbation.

Influence of preexercise muscle glycogen content on transcriptional activity of metabolic and myogenic genes in well-trained humans

To determine whether pre-exercise muscle glycogen content influences the transcription of several early-response genes involved in the regulation of muscle growth, seven male strength-trained subjects performed one-legged cycling exercise to exhaustion to lower muscle glycogen levels (Low) in one leg compared with the leg with normal muscle glycogen (Norm) and then the following day completed a unilateral bout of resistance training (RT). Muscle biopsies from both legs were taken at rest, immediately after RT, and after 3 h of recovery. Resting glycogen content was higher in the control leg (Norm leg) than in the Low leg (435 ± 87 vs. 193 ± 29 mmol/kg dry wt; P < 0.01). RT decreased glycogen content in both legs (P < 0.05), but postexercise values remained significantly higher in the Norm than the Low leg (312 ± 129 vs. 102 ± 34 mmol/kg dry wt; P < 0.01). GLUT4 (3-fold; P < 0.01) and glycogenin mRNA abundance (2.5-fold; not significant) were elevated at rest in the Norm leg, but such differences were abolished after exercise. Preexercise mRNA abundance of atrogenes was also higher in the Norm compared with the Low leg [atrogin: ?14-fold, P < 0.01; RING (really interesting novel gene) finger: ?3-fold, P < 0.05] but decreased for atrogin in Norm following RT (P < 0.05). There were no differences in the mRNA abundance of myogenic regulatory factors and IGF-I in the Norm compared with the Low leg. Our results demonstrate that 1) low muscle glycogen content has variable effects on the basal transcription of select metabolic and myogenic genes at rest, and 2) any differences in basal transcription are completely abolished after a single bout of heavy resistance training. We conclude that commencing resistance exercise with low muscle glycogen does not enhance the activity of genes implicated in promoting hypertrophy.

Early signaling responses to divergent exercise stimuli in skeletal muscle from well-trained humans

Skeletal muscle from strength- and endurance-trained individuals represents diverse adaptive states. In this regard, AMPK-PGC-1α signaling mediates several adaptations to endurance training, while up-regulation of the Akt-TSC2-mTOR pathway may underlie increased protein synthesis after resistance exercise. We determined the effect of prior training history on signaling responses in seven strength-trained and six endurance-trained males who undertook 1 h cycling at 70% VO2peak or eight sets of five maximal repetitions of isokinetic leg extensions. Muscle biopsies were taken at rest, immediately and 3 h postexercise. AMPK phosphorylation increased after cycling in strength-trained (54%; P<0.05) but not endurance-trained subjects. Conversely, AMPK was elevated after resistance exercise in endurance- (114%; P<0.05), but not strengthtrained subjects. Akt phosphorylation increased in endurance- (50%; P<0.05), but not strengthtrained subjects after cycling but was unchanged in either group after resistance exercise. TSC2 phosphorylation was decreased (47%; P<0.05) in endurance-trained subjects following resistance exercise, but cycling had little effect on the phosphorylation state of this protein in either group. p70S6K phosphorylation increased in endurance- (118%; P<0.05), but not strength-trained subjects after resistance exercise, but was similar to rest in both groups after cycling. Similarly, phosphorylation of S6 protein, a substrate for p70 S6K, was increased immediately following resistance exercise in endurance- (129%; P<0.05), but not strength-trained subjects. In conclusion, a degree of “response plasticity” is conserved at opposite ends of the endurancehypertrophic adaptation continuum. Moreover, prior training attenuates the exercise specific signaling responses involved in single mode adaptations to training.