THE ADAPTIVE SSC: FROM FATIGUE RUNS ON EARTH TO THE REBOUNDS ON MARS

In natural forms of ground locomotion such as running and jumping, the functional phases include the stretching of the preactivated muscles followed by their shortening. This is called stretch-shortening cycle (SSC). SSC is a natural but complex activity that combines the available structuro-functional resources: the contractile and elastic structures with the central and reflex activation patterns. SSC may thus be used as a model to reveal the neural adjustments and the associated muscle-tendon responses to internal and external constraints. This presentation will focus on the neuro-mechanical adjustments to the acute and delayed SSC fatigue effects and to partial unweighting on lower body positive pressure treadmill. Both testing conditions emphasize the adaptive quality of the SSC, and demonstrate Time-, Task- and SSC phase-dependent neuro-mechanical adjustments

IDENTIFICATION OF STRETCH-SHORTENING CYCLES IN DIFFERENT SPORTS

In sports the stretch-shortening cycle (SSC) muscle actions are obviously natural. They are partly responsible for making the muscular performance more economical and/or better as compared to the use of isolated forms of muscle actions. In sport activities SSC can be traditionally identified by certain kinematic and electromyographic methods. An attempt is made to describe how one can go beyond these more simple ways by applying portable ultrasonography (US) to record fascicle-tendon interactions during various movements ranging in intensity from low to maximum. The observed results from a number of studies indicate that the original definition of SSC cannot be used to describe the SSC at the MTU levels of all muscles and all exercise conditions. However, the greatest merit of this US application is in its strength to explain more of the mechanism how the fascicle-tendon interaction differs between muscles and how the elastic energy may be involved in the performance potentiation

ARCHITECTURAL DIFFERENCES OF LOWER LIMB MUSCLE-TENDON FOR MONOZYGOTIC TWINS WITH DIFFERENT SPORT EXPERIENCES

The purpose of this study was to examine architectural differences of lower limb muscle-tendon for monozygotic twins with different sport experiences and for monozygotic twins with same sport experiences. 50 monozygotic twins (MZT) participated in this study, consisting of 16 MZT with different sport experiences, 34 MZT with same sport experiences. Musculoskeletal ultrasonography is applied to measure the muscle fascicle length of gastrocnemius medialis (GM) muscle as well as Achilles and patella tendon cross-sectional area (CSA) and length. Achilles tendon was separately measured from the AT insertion point on the calcaneus to the distal end of soleus muscle (ATSOL) and to the AT junction between medial and lateral gastrocnemii muscles (ATGML), respectively. The measured intraclass correlation coefficient (ICC) clearly showed poor concordances in the ATSOL length of MZT with different sport experiences (ICC of 0.74), and good concordance in the MG fascicle length of MZT with different sport experiences (ICC of 0.83). Other parameters in all intra-pears showed excellent concordances (ICC\u3e0.9). Thus, different concordances of AT length between GM and SOL parts can indicate the different plasticity by the structural and functional mechanics and different concordances between groups indicate that ATSOL and GM fascicle length are affected not only by genetic factors but also by acquired environmental factors

Neuromuscular mechanics and hopping training in elderly

Purpose: The present study examined the effects of repetitive hopping training on muscle activation profiles and fascicle–tendon interaction in the elderly.Methods: 20 physically active elderly men were randomly assigned for training (TG) and control groups (CG). TG performed supervised bilateral short contact hopping training with progressively increasing training volume. Measurements were performed before the training period (BEF) as well as after 2 weeks (2 W) and 11 weeks (11 W) of training. During measurements, the gastrocnemius medialis–muscle (GaM) fascicle and its outer Achilles tendon length changes during hopping were examined by ultrasonography together with electromyographic (EMG) activities of calf muscles, kinematics, and kinetics.Results: At 2 W, the ankle joint stiffness was increased by 21.0 ± 19.3 % and contact time decreased by 9.4 ± 7.8 % in TG. Thereafter, from 2–11 W the jumping height increased 56.2 ± 18.1 % in TG. Simultaneously, tendon forces increased 24.3 ± 19.0 % but tendon stiffness did not change. GaM fascicles shifted to shorter operating lengths after training without any changes in their length modifications during the contact phase of hopping. Normalized EMG amplitudes during hopping did not change with training.Conclusions: The present study shows that 11 W of hopping training improves the performance of physically active elderly men. This improvement is achieved with shorter GaM operating lengths and, therefore, increased fascicle stiffness and improved tendon utilization after training. Based on these results, hopping training could be recommended for healthy fit elderly to retain and improve rapid force production capacity. © 2014 Springer-Verlag Berlin Heidelber

Short-term bone biochemical response to a single bout of high-impact exercise

Bone response to a single bout of exercise can be observed with biochemical markers of bone formation and resorption. The purpose of this study was to examine the response of bone biochemical markers to a single bout of exhaustive high-impact exercise. 15 physically active young subjects volunteered to participate. The subjects performed continuous bilateral jumping with the ankle plantarflexors at 65 % of maximal ground reaction force (GRF) until exhaustion. Loading was characterized by analyzing the GRF recorded for the duration of the exercise. Venous blood samples were taken at baseline, immediately after, 2h and on day 1 and day 2 after the exercise. Procollagen type I amino terminal propeptide (P1NP, marker of bone formation) and carboxyterminal crosslinked telopeptide (CTx, marker of bone resorption) were analyzed from the blood samples. CTx increased significantly (32 %, p = 0.015) two days after the exercise and there was a tendensy towards increase seen in P1NP (p = 0.053) one day after the exercise. A significant positive correlation (r = 0.49 to 0.69, p &le; 0.038) was observed between change in P1NP from baseline to day 1 and exercise variables (maximal slope of acceleration, body weight (BW) adjusted maximal GRF, BW adjusted GRF exercise intensity and osteogenic index). Based on the two biochemical bone turnover markers, it can be concluded that bone turnover is increased in response to a very<br /

Achilles tendon length changes during walking in long-term diabetes patients

Background Diabetes leads to numerous side effects, including an increased density of collagen fibrils and thickening of the Achilles tendon. This may increase tissue stiffness and could affect stretch distribution between muscle and tendinous tissues during walking. The primary aim of this study was to examine stretch distribution between muscle and tendinous tissues in the medial gastrocnemius muscle-tendon unit in long-term diabetes patients and control subjects during walking. Methods Achilles tendon length changes were investigated in 13 non-neuropathic diabetes patients and 12 controls, whilst walking at a self selected speed across a 10 m force platform. Electromyographic activity was recorded in the medial gastrocnemius, soleus and tibialis anterior muscles, goniometers were used to detect joint angle changes, and ultrasound was used to estimate tendon length changes. Findings Achilles tendon length changes were attenuated in diabetes patients compared to controls, and were inversely correlated with diabetes duration (r = -0.628; P < 0.05), as was ankle range of motion (r = -0.693; P < 0.01). Tendon length changes were also independent of walking speed (r = -0.299; P = 0.224) and age (r = 0.115; P = 0.721) in the diabetic group. Interpretation Stretch distribution between muscle and tendon during walking is altered in diabetic patients, which could decrease walking efficiency, a factor that may be exacerbated with increasing diabetes duration. Diabetes-induced changes in mechanical tendon properties may be at least partly responsible for attenuated tendon length changes during walking in this patient group.No Full Tex

Stretch-shortening cycle : a power model to study normal and fatigued muscle

Revue de synthèse des travaux concernant : l'utilisation des mesures de force in vivo pour caractériser le cycle étirement-raccourcissement lors de la locomotion humaine ; la contribution des réflexes d'étirement à l'augmentation de la force lors du cycle étirement-raccourcissement ; l'utilisation du SSC pour étudier la fatigue neuromusculair

Stretch-shortening cycle : a power model to study normal and fatigued muscle

Revue de synthèse des travaux concernant : l'utilisation des mesures de force in vivo pour caractériser le cycle étirement-raccourcissement lors de la locomotion humaine ; la contribution des réflexes d'étirement à l'augmentation de la force lors du cycle étirement-raccourcissement ; l'utilisation du SSC pour étudier la fatigue neuromusculair