Structure and function of Achilles and patellar tendons following moderate slow resistance training in young and old men.

The aim of this study was to investigate the effect of aging and resistance training with a moderate load on the size and mechanical properties of the patellar (PT) and Achilles tendon (AT) and their associated aponeuroses; medial gastrocnemius (MG) and vastus lateralis (VL). Young (Y55; 24.8 ± 3.8 yrs, n = 11) and old men (O55; 70.0 ± 4.6 yrs, n = 13) were assigned to undergo a training program (12 weeks; 3 times/week) of moderate slow resistance training [55% of one repetition maximum (RM)] of the triceps surae and quadriceps muscles. Tendon dimensions were assessed using 1.5 T magnetic resonance imaging before and after 12 weeks. AT and PT cross sectional area (CSA) were determined every 10% of tendon length. Mechanical properties of the free AT, MG aponeurosis, PT, and VL aponeurosis were assessed using ultrasonography (deformation) and tendon force measurements. CSA of the AT but not PT was greater in O55 compared with Y55. At baseline, mechanical properties were generally lower in O55 than Y55 for AT, MG aponeurosis and VL aponeurosis (Young's modulus) but not for PT. CSA of the AT and PT increased equally in both groups following training. Further, for a given force, stiffness and Young's modulus also increased equally for VL aponeurosis and AT, for boths groups. The present study highlights that except for the PT, older men have lower tendon (AT, MG aponeurosis, and VL aponeurosis) mechanical properties than young men and 12-weeks of moderate slow resistance training appears sufficient to improve tendon size and mechanical adaptations in both young and older men. New and Noteworthy: These novel findings suggest that short-term moderate slow resistance training induces equal improvements in tendon size and mechanics regardless of age.

Muscles adaptation to aging and training: architectural changes - a randomised trial.

BACKGROUND: To investigate how anatomical cross-sectional area and volume of quadriceps and triceps surae muscles were affected by ageing, and by resistance training in older and younger men, in vivo. METHODS: The old participants were randomly assigned to moderate (O55, n = 13) or high-load (O80, n = 14) resistance training intervention (12 weeks; 3 times/week) corresponding to 55% or 80% of one repetition maximum, respectively. Young men (Y55, n = 11) were assigned to the moderate-intensity strengthening exercise program. Each group received the exact same training volume on triceps surae and quadriceps group (Reps x Sets x Intensity). The fitting polynomial regression equations for each of anatomical cross-sectional area-muscle length curves were used to calculate muscle volume (contractile content) before and after 12 weeks using magnetic resonance imaging scans. RESULTS: Only Rectus femoris and medial gastrocnemius muscle showed a higher relative anatomical cross-sectional area in the young than the elderly on the proximal end. The old group displayed a higher absolute volume of non-contractile material than young men in triceps surae (+ 96%). After training, Y55, O55 and O80 showed an increase in total quadriceps (+ 4.3%; + 6.7%; 4.2% respectively) and triceps surae (+ 2.8%; + 7.5%; 4.3% respectively) volume. O55 demonstrated a greater increase on average gains compared to Y55, while no difference between O55 and O80 was observed. CONCLUSIONS: Muscle loss with aging is region-specific for some muscles and uniform for others. Equivalent strength training volume at moderate or high intensities increased muscle volume with no differences in muscle volume gains for old men. These data suggest that physical exercise at moderate intensity (55 to 60% of one repetition maximum) can reverse the aging related loss of muscle mass. TRIAL REGISTRATION: NCT03079180 in ClinicalTrials.gov . Registration date: March 14, 2017.

Multiscale-Engineered Muscle Constructs: PEG Hydrogel Micro-Patterning on an Electrospun PCL Mat Functionalized with Gold Nanoparticles.

The development of new, viable, and functional engineered tissue is a complex and challenging task. Skeletal muscle constructs have specific requirements as cells are sensitive to the stiffness, geometry of the materials, and biological micro-environment. The aim of this study was thus to design and characterize a multi-scale scaffold and to evaluate it regarding the differentiation process of C2C12 skeletal myoblasts. The significance of the work lies in the microfabrication of lines of polyethylene glycol, on poly(ε-caprolactone) nanofiber sheets obtained using the electrospinning process, coated or not with gold nanoparticles to act as a potential substrate for electrical stimulation. The differentiation of C2C12 cells was studied over a period of seven days and quantified through both expression of specific genes, and analysis of the myotubes' alignment and length using confocal microscopy. We demonstrated that our multiscale bio-construct presented tunable mechanical properties and supported the different stages skeletal muscle, as well as improving the parallel orientation of the myotubes with a variation of less than 15°. These scaffolds showed the ability of sustained myogenic differentiation by enhancing the organization of reconstructed skeletal muscle. Moreover, they may be suitable for applications in mechanical and electrical stimulation to mimic the muscle's physiological functions.

Achilles Tendon Adaptation to Neuromuscular Electrical Stimulation: Morphological and Mechanical Changes.

It remains unclear whether neuromuscular electrical stimulation can induce sufficient tendon stress to lead to tendon adaptations. Thus, we investigated the effect of such a training program on the triceps surae muscle following the morphological and mechanical properties of the Achilles tendon. Eight men participated in a 12-week high-frequency neuromuscular electrical stimulation training program of the triceps surae muscle under isometric conditions. Ultrasonography was used pre- and post-intervention to quantify cross-sectional area, free length, and total length of the Achilles tendon, as well as the myotendinous junction elongation during a maximal isometric ramp contraction under plantar flexion. Neuromuscular electrical stimulation training does not lead to changes in Achilles tendon free and total length, cross-sectional area, or maximal elongation capacity. However, a significant increase was evidenced in maximal tendon force post-training (+25.2%). Hence, Young's Modulus and maximal stress were significantly greater after training (+12.4% and +23.4%, respectively). High-frequency neuromuscular electrical stimulation training induces repeated stress sufficient to lead to adaptations of mechanical properties of the Achilles tendon. Thus, this training technique may be of particular interest as a new rehabilitation method in tendinopathy management or to counteract the effect of hypo-activity.

Optimized scoring tool to quantify the functional performance during the sit-to-stand transition with a magneto-inertial measurement unit.

BACKGROUND: Sit-to-stand is used as a qualitative test to evaluate functional performance, especially to detect fall risks and frail individuals. The use of various quantitative criteria would enable a better understanding of musculoskeletal deficits and movement strategy modifications. This quantification was proven possible with a magneto-inertial unit which provides a compatible wearable device for clinical routine motion analysis. METHODS: Sit-to-stand movements were recorded using a single magneto-inertial measurement unit fixed on the chest for 74 subjects in three groups healthy young, healthy senior and frail. MIMU data was used to compute 15 spatiotemporal, kinematic and energetic parameters. Nonparametric statistical test showed a significant influence of age and frailness. After reducing the number of parameters by a principal component analysis, an AgingScore and a FrailtyScore were computed. FINDINGS: The fraction of variance explained by the first principal component was 77.48 ±â€¯2.80% for principal component analysis with healthy young and healthy senior groups, and 74.94 ±â€¯2.24% with healthy and frail senior groups. By receiver operating characteristic curve analysis of this score, we were able to refine the analysis to differentiate between healthy young and healthy senior subjects as well as healthy senior and frail subjects. By radar plot of the most discriminate parameters, the motion's strategy could be characterized and be used to detect premature functional deficit or frail subjects. INTERPRETATION: Sit-to-stand measured by a single magneto-inertial unit and dedicated post processing is able to quantify subject's musculoskeletal performance and will allow longitudinal investigation of aging population.

Biomaterials in Tendon and Skeletal Muscle Tissue Engineering: Current Trends and Challenges.

Tissue engineering is a promising approach to repair tendon and muscle when natural healing fails. Biohybrid constructs obtained after cells’ seeding and culture in dedicated scaffolds have indeed been considered as relevant tools for mimicking native tissue, leading to a better integration in vivo. They can also be employed to perform advanced in vitro studies to model the cell differentiation or regeneration processes. In this review, we report and analyze the different solutions proposed in literature, for the reconstruction of tendon, muscle, and the myotendinous junction. They classically rely on the three pillars of tissue engineering, i.e., cells, biomaterials and environment (both chemical and physical stimuli). We have chosen to present biomimetic or bioinspired strategies based on understanding of the native tissue structure/functions/properties of the tissue of interest. For each tissue, we sorted the relevant publications according to an increasing degree of complexity in the materials’ shape or manufacture. We present their biological and mechanical performances, observed in vitro and in vivo when available. Although there is no consensus for a gold standard technique to reconstruct these musculo-skeletal tissues, the reader can find different ways to progress in the field and to understand the recent history in the choice of materials, from collagen to polymer-based matrices.

Investigation of the HD-sEMG probability density function shapes with varying muscle force using data fusion and shape descriptors.

This work presents an evaluation of the High Density surface Electromyogram (HD-sEMG) Probability Density Function (PDF) shape variation according to contraction level. On that account, using PDF shape descriptors: High Order Statistics (HOS) and Shape Distances (SD), we try to address the absence of a consensus for the sEMG non-Gaussianity evolution with force variation. This is motivated by the fact that PDF shape information are relevant in physiological assessment of the muscle architecture and function, such as contraction level classification, in complement to classical amplitude parameters. Accordingly, both experimental and simulation studies are presented in this work. For data fusion, the watershed image processing technique was used. This technique allowed us to find the dominant PDF shape variation profiles from the 64 signals. The experimental protocol consisted of three isometric isotonic contractions of 30, 50 and 70% of the Maximum Voluntary Contraction (MVC). This protocol was performed by six subjects and recorded using an 8 × 8 HD-sEMG grid. For the simulation study, the muscle modeling was done using a fast computing cylindrical HD-sEMG generation model. This model was personalized by morphological parameters obtained by sonography. Moreover, a set of the model parameter configurations were compared as a focused sensitivity analysis of the PDF shape variation. Further, monopolar, bipolar and Laplacian electrode configurations were investigated in both experimental and simulation studies. Results indicated that sEMG PDF shape variations according to force increase are mainly dependent on the Motor Unit (MU) spatial recruitment strategy, the MU type distribution within the muscle, and the used electrode arrangement. Consequently, these statistics can give us an insight into non measurable parameters and specifications of the studied muscle primarily the MU type distribution.

The Differential Hormonal Milieu of Morning versus Evening May Have an Impact on Muscle Hypertrophic Potential.

Substantial gains in muscle strength and hypertrophy are clearly associated with the routine performance of resistance training. What is less evident is the optimal timing of the resistance training stimulus to elicit these significant functional and structural skeletal muscle changes. Therefore, this investigation determined the impact of a single bout of resistance training performed either in the morning or evening upon acute anabolic signalling (insulin-like growth factor-binding protein-3 (IGFBP-3), myogenic index and differentiation) and catabolic processes (cortisol). Twenty-four male participants (age 21.4±1.9yrs, mass 83.7±13.7kg) with no sustained resistance training experience were allocated to a resistance exercise group (REP). Sixteen of the 24 participants were randomly selected to perform an additional non-exercising control group (CP) protocol. REP performed two bouts of resistance exercise (80% 1RM) in the morning (AM: 0800 hrs) and evening (PM: 1800 hrs), with the sessions separated by a minimum of 72 hours. Venous blood was collected immediately prior to, and 5 min after, each resistance exercise and control sessions. Serum cortisol and IGFBP-3 levels, myogenic index, myotube width, were determined at each sampling period. All data are reported as mean ± SEM, statistical significance was set at P≤0.05. As expected a significant reduction in evening cortisol concentration was observed at pre (AM: 98.4±10.5, PM: 49.8±4.4 ng/ml, P<0.001) and post (AM: 98.0±9.0, PM: 52.7±6.0 ng/ml, P<0.001) exercise. Interestingly, individual cortisol differences pre vs post exercise indicate a time-of-day effect (AM difference: -2±2.6%, PM difference: 14.0±6.7%, P = 0.03). A time-of-day related elevation in serum IGFBP-3 (AM: 3274.9 ± 345.2, PM: 3605.1 ± 367.5, p = 0.032) was also evident. Pre exercise myogenic index (AM: 8.0±0.6%, PM: 16.8±1.1%) and myotube width (AM: 48.0±3.0, PM: 71.6±1.9 µm) were significantly elevated (P<0.001) in the evening. Post exercise myogenic index was greater AM (11.5±1.6%) compared with PM (4.6±0.9%). No difference was observed in myotube width (AM: 48.5±1.5, PM: 47.8±1.8 µm) (P>0.05). Timing of resistance training regimen in the evening appears to augment some markers of hypertrophic potential, with elevated IGFBP-3, suppressed cortisol and a superior cellular environment. Further investigation, to further elucidate the time course of peak anabolic signalling in morning vs evening training conditions, are timely.

Human Achilles tendon glycation and function in diabetes.

Diabetic patients have an increased risk of foot ulcers, and glycation of collagen may increase tissue stiffness. We hypothesized that the level of glycemic control (glycation) may affect Achilles tendon stiffness, which can influence gait pattern. We therefore investigated the relationship between collagen glycation, Achilles tendon stiffness parameters, and plantar pressure in poorly (n = 22) and well (n = 22) controlled diabetic patients, including healthy age-matched (45-70 yr) controls (n = 11). There were no differences in any of the outcome parameters (collagen cross-linking or tendon stiffness) between patients with well-controlled and poorly controlled diabetes. The overall effect of diabetes was explored by collapsing the diabetes groups (DB) compared with the controls. Skin collagen cross-linking lysylpyridinoline, hydroxylysylpyridinoline (136%, 80%, P < 0.01) and pentosidine concentrations (55%, P < 0.05) were markedly greater in DB. Furthermore, Achilles tendon material stiffness was higher in DB (54%, P < 0.01). Notably, DB also demonstrated higher forefoot/rearfoot peak-plantar-pressure ratio (33%, P < 0.01). Overall, Achilles tendon material stiffness and skin connective tissue cross-linking were greater in diabetic patients compared with controls. The higher foot pressure indicates that material stiffness of tendon and other tissue (e.g., skin and joint capsule) may influence foot gait. The difference in foot pressure distribution may contribute to the development of foot ulcers in diabetic patients.

Life-long endurance running is associated with reduced glycation and mechanical stress in connective tissue.

Life-long regular endurance exercise is known to counteract the deterioration of cardiovascular and metabolic function and overall mortality. Yet it remains unknown if life-long regular endurance exercise can influence the connective tissue accumulation of advanced glycation endproducts (AGEs) that is associated with aging and lifestyle-related diseases. We therefore examined two groups of healthy elderly men: 15 master athletes (64 ± 4 years) who had been engaged in life-long endurance running and 12 old untrained (66 ± 4 years) together with two groups of healthy young men; ten young athletes matched for running distance (26 ± 4 years), and 12 young untrained (24 ± 3 years). AGE cross-links (pentosidine) of the patellar tendon were measured biochemically, and in the skin, it was assessed by a fluorometric method. In addition, we determined mechanical properties and microstructure of the patellar tendon. Life-long regular endurance runners (master athletes) had a 21 % lower AGE cross-link density compared to old untrained. Furthermore, both master athletes and young athletes displayed a thicker patellar tendon. These cross-sectional data suggest that life-long regular endurance running can partly counteract the aging process in connective tissue by reducing age-related accumulation of AGEs. This may not only benefit skin and tendon but also other long-lived protein tissues in the body. Furthermore, it appears that endurance running yields tendon tissue hypertrophy that may serve to lower the stress on the tendon and thereby reduce the risk of injury.

Influence of exercise intensity on training-induced tendon mechanical properties changes in older individuals.

This study compared the effects of low vs. high intensity training on tendon properties in an elderly population. Participants were pair-matched (gender, habitual physical activity, anthropometrics, and baseline knee extension strength) and then randomly assigned to low (LowR, i.e., ~40 % 1RM) or high (High R, i.e., ~80 % 1RM) intensity resistance training programmes for 12 weeks, 3× per week (LowR, n = 9, age 74 ± 5 years; HighR, n = 8, age 68 ± 6 years). Patellar tendon properties (stiffness [K], Young's modulus [YM], cross-sectional area [T CSA], and tendon length [T L]) were measured pre and post training using a combination of magnetic resonance imaging (MRI), B-mode ultrasonography, dynamometry, electromyography and ramped isometric knee extensions. With training K showed no significant change in the LowR group while it incremented by 57.7 % in the HighR group (p < 0.05). The 51.1 % group difference was significant (p < 0.05). These differences were still apparent when the data was normalized for T CSA and T L, i.e., significant increase in YM post-intervention in HighR (p < 0.05), but no change in LowR. These findings suggest that when prescribing exercise for a mixed genders elderly population, exercise intensities of ≤40 % 1RM may not be sufficient to affect tendon properties.

Changes in contractile and elastic properties of the triceps surae muscle induced by neuromuscular electrical stimulation training.

PURPOSE: Neuromuscular electrical stimulation (NMES) training is known to induce improvement in force production capacities and fibre-type transition. The aim of this study was to determine whether NMES training also leads to changes in the mechanical properties of the human triceps surae (TS) muscle. METHODS: Fifteen young male subjects performed a training protocol (4 weeks, 18 sessions, 4-5 sessions per week) based on a high-frequency isometric NMES programme of TS muscle. Quick-release test was used to evaluate Musculo-Tendinous (MT) stiffness index (SIMT) as the slope of the linear MT stiffness-torque relationships under submaximal contraction. Sinusoidal perturbations allowed the assessment of musculo-articular stiffness index (SIMA) as well as the calculation of the maximal angular velocity ([Formula: see text]) of TS muscle using an adaptation of Hill's equation. RESULTS: After NMES training, Maximal Voluntary Contraction under isometric conditions and [Formula: see text] increased significantly by 17.5 and 20.6 %, respectively, while SIMT and SIMA decreased significantly (-12.7 and -9.3 %, respectively). CONCLUSIONS: These changes in contractile and elastic properties may lead to functional changes of particular interest in sport-related activities as well as in the elderly.

Comparative effect of a 1 h session of electrical muscle stimulation and walking activity on energy expenditure and substrate oxidation in obese subjects.

It has previously been shown that low-frequency neuromuscular electrical stimulation (NMES) techniques can induce increases in energy expenditure similar to those associated with exercise. This study investigated the metabolic and cardiovascular effects of a 1 h session of lower limb NMES and compared cardiovascular response with that observed during walking in nine obese subjects (three males) (age = 43.8 ± 3.0 years; body mass index (BMI) = 41.5 ± 1.8 kg/m(2)). The NMES protocol consisted of delivering a complex pulse pattern to the thigh muscles for 1 h. The walking test consisted of five 4-min bouts starting at 2 km/h with 1 km/h increments up to 6 km/h. In both tests, an open-circuit gas analyser was used to assess O(2) consumption ([Formula: see text]O(2)), CO(2) production ([Formula: see text]CO(2)), respiratory exchange ratio (RER), and heart rate (HR). Rates of fat oxidation (RFO) and carbohydrate oxidation (CHO) were estimated by indirect calorimetry. One hour of NMES significantly increased [Formula: see text]O(2), HR, RER, and mean energy expenditure compared with resting values, reaching 8.7 ± 1.3 mL·min(-2)·kg(-1) (47% of [Formula: see text]O(2peak)), 114.8 ± 7.5 bpm, 0.95, and 318.5 ± 64.3 kcal/h, respectively. CHO, but not RFO, increased during 1 h of NMES. With NMES, CHO was greater and RFO was less than at all walking speeds except 6 km/h. Lactate also increased more with NMES, to 3.5 ± 0.7 mmol versus a maximum of 1.5 ± 0.3 mmol with the walking protocol. These results suggest that NMES can be used in an obese population to induce an effective cardiovascular exercise response. In fact, the observed increase in energy expenditure induced by 1 h of NMES is clinically important and comparable with that recommended in weight management programs.

Neuromuscular electrical stimulation can elicit aerobic exercise response without undue discomfort in healthy physically active adults.

Recent studies have suggested that subtetanic neuromuscular electrical stimulation (NMES) protocols applied to the quadriceps and hamstrings may have potential as an alternative aerobic exercise modality. However, its tolerability and effectiveness in the physically active population has been questioned. The primary purpose of this study was to measure physiological and subjective responses to a modified subtetanic NMES protocol in a physically active adult population. Furthermore, the effect of habituation to stimulation on tolerability, the repeatability of response on separate days, and the differences in male and female responses to stimulation were assessed. Oxygen uptake (V[Combining Dot Above]O(2)), heart rate (HR), blood lactate (BLa), rate of perceived exertion, and subjective discomfort were measured in 16 participants (8 men and 8 women) throughout a subtetanic NMES protocol performed at incremental intensities to subjective comfort threshold on 2 separate days, before and after 9 NMES habituation sessions. Peak physiological responses observed at subjective comfort threshold were consistent with therapeutic aerobic exercise intensities (51.5 ± 10.9% V[Combining Dot Above]O(2)max; 72.0 ± 10.9% HRmax; 4.7 ± 2.7 mMol BLa). Peak V[Combining Dot Above]O(2) and current intensity achieved were significantly higher (p < 0.05), yet perceived discomfort was unchanged, after the period of habituation. However, physiological and subjective responses at equivalent stimulation intensities remained unchanged on different days. Male participants showed higher values than female participants. These results suggest that subtetanic NMES can elicit a consistent aerobic exercise response without undue discomfort and could be considered as an alternative exercise modality.

Are H-reflex and M-wave recruitment curve parameters related to aerobic capacity?

Soleus Hoffmann reflex (H-reflex) amplitude is affected by a training period and type and level of training are also well known to modify aerobic capacities. Previously, paired changes in H-reflex and aerobic capacity have been evidenced after endurance training. The aim of this study was to investigate possible links between H- and M-recruitment curve parameters and aerobic capacity collected on a cohort of subjects (56 young men) that were not involved in regular physical training. Maximal H-reflex normalized with respect to maximal M-wave (H(max)/M(max)) was measured as well as other parameters of the H- or M-recruitment curves that provide information about the reflex or direct excitability of the motoneuron pool, such as thresholds of stimulus intensity to obtain H or M response (H(th) and M(th)), the ascending slope of H-reflex, or M-wave recruitment curves (H(slp) and M(slp)) and their ratio (H(slp)/M(slp)). Aerobic capacity, i.e., maximal oxygen consumption and maximal aerobic power (MAP) were, respectively, estimated from a running field test and from an incremental test on a cycle ergometer. Maximal oxygen consumption was only correlated with M(slp), an indicator of muscle fiber heterogeneity (p < 0.05), whereas MAP was not correlated with any of the tested parameters (p > 0.05). Although higher H-reflex are often described for subjects with a high aerobic capacity because of endurance training, at a basic level (i.e., without training period context) no correlation was observed between maximal H-reflex and aerobic capacity. Thus, none of the H-reflex or M-wave recruitment curve parameters, except M(slp), was related to the aerobic capacity of young, untrained male subjects.

Is there a morning-to-evening difference in the acute IL-6 and cortisol responses to resistance exercise?

Exercise training is known to induce a molecular adaptation process involving inflammatory responses. However any time-of-day effect of exercise on inflammatory responses remains unknown. The aim of the present study was to investigate whether acute bouts of intense exercise performed at different times of the day would affect the release Interleukin-6 (IL-6), one of the most abundant cytokines in mammalian endocrine response to exercise. Cortisol levels were measured as a confirmation of correct timing of exercise and to determine any impact it may have on the cytokine release. Twelve healthy male participants carried out 30 min of intense exercise (3 sets of 8-12 repetitions for 4 resistance exercises at 70% of 1RM) in morning (08:15-09:00 h), and evening (18:15-19:00 h) sessions. An 8h fasting period was required before each exercise session. Blood samples were taken immediately pre and post each exercise sessions to determine IL-6 and cortisol levels. Our data show that whilst the training group showed no post-exercise changes in serum_IL-6 levels (P>0.05), the control group on the other hand showed significant time-of-day modifications in serum_IL-6 levels (P=0.008). Moreover, a significant interaction between intervention phase (pre-post training, AM vs. PM) and group (Exercise vs. Control) is evidenced in terms of serum_IL-6 levels (P=0.014). This interaction however was nullified when the between group differences at baseline were partialled out in a covariate analysis (P>0.05). We also found that the main effect of experimental phase on Cortisol was present in both the trained (P=0.004) and control groups (p<0.001) with no significant interaction (P>0.05). Based on the current data, we would propose that exercise and/or time-of-day would not interfere with clinical endocrine profiling of IL-6 in a population.

Follow-up of ankle stiffness and electromechanical delay in immobilized children: three cases studies.

Clinical manual tests refer to increased ankle stiffness in children immobilized due to hip osteochondritis. The aim of the present study was to investigate musculo-articular stiffness via different techniques in immobilized children to confirm or not and quantify these observations. Ankle stiffness was quantified monthly during the long immobilization period in three diseased children and compared to healthy age-matched children. Sinusoidal perturbations were used to evaluate musculo-articular (MA) stiffness of the ankle plantar-flexors. The stiffness index (SI(MA-EMG)) was the slope of the linear relationship between angular stiffness and plantar-flexion torque normalized with electromyographic activity of the triceps surae (TS). The stiffness of the ankle plantar-flexors was also indirectly evaluated using the TS electromechanical delay (EMD). SI(MA-EMG) was greater for diseased children, and this higher stiffness was confirmed by the higher EMD values found in these immobilized children. Furthermore, both parameters indicated that ankle stiffness continues to increase through immobilization period. This study gives a quantitative evaluation of ankle stiffness changes through the immobilization period imposed to children treated for hip osteochondritis. The use of EMD measurement to indirectly evaluate these stiffness changes is also validated. This study shed for the first time some light into the patterns of muscle modifications following immobilization in children.

Paired changes in electromechanical delay and musculo-tendinous stiffness after endurance or plyometric training.

When measured in vivo electromechanical delay (EMD) depends mainly on the elastic properties of the muscle-tendon unit. Recent studies have shown changes in stiffness of the triceps surae (TS) following a period of training. To confirm the influence of musculo-tendinous stiffness on EMD, this study investigates paired changes in these two parameters after a training period. Two types of training known to induce opposite changes in stiffness were analysed. EMD and musculo-tendinous stiffness were measured on adult subjects before and after 10 weeks of endurance (n = 21) or plyometric (n = 9) trainings. EMD was defined as the time lag between the TS M-wave latency and the onset of muscle twitch evoked at rest by supramaximal electrical stimulations of the posterior tibial nerve. Quick release tests were used to evaluate the musculo-tendinous stiffness of the ankle plantar flexors. The stiffness index was defined as the slope of the relationship between angular stiffness and external torque values. Endurance training, known to preferentially activate the slow, stiffer muscle fibers, leads to a decrease in EMD and to an increase in stiffness index. Following plyometric training, which specifically recruits fast, more compliant fibers, EMD and the stiffness index exhibited adaptations directionally opposite to those seen with endurance training. When pooling the data for the two subject groups, a correlation was found between changes in EMD and changes in musculo-tendinous stiffness indexes. Thus, changes in EMD values are proposed to indirectly link to changes in musculo-tendinous stiffness for subjects involved in muscle training.

Effect of foot and ankle immobilization on leg and thigh muscles' volume and morphology: a case study using magnetic resonance imaging.

Our aim was to determine the time course of any changes in muscle volume and shape in the lower limbs following immobilization. A healthy young woman (29 years) had suffered a fracture of the fifth metatarsal of the right foot. MRI scanning of her right thigh and calf muscles had been performed 1 month before the injury (Pre) during a scan initially planned as a teaching tool, 2 days following a 4-week immobilization period (Post), and after a 2-month recovery period (Post+2). The results show muscle volume decrements in the triceps surae (TS), quadriceps (Quad), and hamstring (Ham) of 21.9%, 24.1%, and 6.5%, respectively, between the Pre and Post measurements. At Post+2, the Quad and TS muscle volumes were still 5.2% and 9.5% lower, compared with the Pre data. The Ham muscle volume, however, was 2.7% greater than at the Pre phase. Following recovery, the increase in individual TS muscles volume was limited to both proximal and medial (with respect to the knee joint) segments of the muscles. These results indicate very substantial and rapid losses in muscle volumes, both proximally and distally to the immobilization site. The results also show that recovery is far from complete up to 2 months post cast removal. The results have implications for the requirements for rehabilitation for orthopedic patients.