Individualized Muscle-Tendon Assessment and Training

The interaction of muscle and tendon is of major importance for movement performance and a balanced development of muscle strength and tendon stiffness could protect athletes from overuse injury. However, muscle and tendon do not necessarily adapt in a uniform manner during a training process. The development of a diagnostic routine to assess both the strength capacity of muscle and the mechanical properties of tendons would enable the detection of muscle-tendon imbalances, indicate if the training should target muscle strength or tendon stiffness development and allow for the precise prescription of training loads to optimize tendon adaptation. This perspective article discusses a framework of individualized muscle-tendon assessment and training and outlines a methodological approach for the patellar tendon.Peer Reviewe

BIOMECHANICAL ANALYSIS OF THE POLE VAULT

INTRODUCTION: The main purposes of this study were to (a) examine the behavior and practical application of 3 criteria in world class pole vaulters and (b) to determine the influence of the starting conditions and athlete's behavior during the pole phase, on performance. Note that the three criteria label the starting conditions of the pole vault and the behavior of athletes during the pole phase. METHODS: Data for this study were gathered at the 1997 Track and Field World Championships in Athens, Greece. Twenty-five successful jumps by 11 participants in the final competition were analyzed. The data for the two-dimensional analysis were recorded using two synchronized stationary video cameras operating at 50 Hz. For the analysis of the data, the pole vault was divided into (a) energy production phase (This phase begins with the approach and ends with the contact of the jump foot and the ground at take-off.) and (b) energy exchange phase (This phase begins with contact of the jump foot and the ground at take-off and ends when the athlete releases the pole at the end of the jump.). RESULTS AND CONCLUSIONS: During the first part of the energy exchange phase, energy is transferred into the pole, reducing the athlete's total energy. The difference between the decrease of the athlete's total energy and the maximum pole energy indicates whether pole elasticity was effectively used (Criterion 1) (see Figure 1). During the second part of the energy exchange phase, the energy is transferred back from the pole to the athlete, increasing the athlete's total energy. The difference between the returned energy and the energy gain of the athlete indicates to what extent the athlete used muscular work to create additional energy (Criterion 2). The approach energy (start energy) represents the starting conditions of the pole vaulter (Criterion 3). From the analyzed jumps, it was possible to create 3 groups which demonstrated similar values for start energy, Criterion 1 and Criterion 2. The results indicate that both individual and group-specific technique deficits of athletes can vary and still produce the same performance. At the elite level, the start energy determines the beginning conditions for good or poor jump performance. The actual jump heights achieved are dependent on the behavior of the vaulter during the energy exchange phase. From the examination of the start energy, Criterion 1 and Criterion 2, it was possible to diagnose the individual technical deficits of the athletes

SYMMETRY AND REPRODUCIBILITY OF KINEMATIC PARAMETERS DURING VARIOUS RUNNING TECHNIQUES

The purpose of this study was to examine the reproducibility and the symmetry of a wide number of kinematic parameters while running with various running techniques. Each of twelve tested persons ran on a treadmill in combinations of three velocities (2.5, 3.0 and 3.5m/s) and three stride frequencies (preferred. +/-10% from preferred). Three cycles were recorded for each running task using a video camera (250 Hz) at each side of the body. Intraclass correlation coefficients (ICC generally> 0.80 ) for both legs were high. Only the angular velocity parameters demonstrated low reproducibility (ICC < 0.75). Significant (P 10%)

BIOMECHANICAL ANALYSIS OF THE HIGH JUMP AT THE SIXTH WCA IN ATHENS

Introduction: The main purposes of this study were 1. To determine the importance of initial conditions and take-off phase characteristics on jump performance. 2. To determine to what extent the initial conditions are effectively used by jumpers at the world class level. Methods: Data for this analysis were collected during the men’s high jump final competition at the 1997 Track and Field World Championships. A total of 26 successful jumps by 12 athletes were analyzed. The data was collected using 4 synchronized video cameras (50 Hz). Results and conclusions: On the basis of the total initial center of mass (CM) energy and the take-off characteristics, two relatively homogeneous groups could be identified. The take-off phase characteristics which are determined by the loss of CM energy during take-off and from the transformation of the approach energy to jump energy (transformation index) are very important for determining jump height. The initial energy of the CM determines the height an athlete can achieve. The actual jump height is strongly influenced by the take-off characteristics of the athlete. Both groups achieved the same jump height. Group 2 produced higher initial energy values. Group 1 demonstrated more efficient take-off characteristics. It was found that many athletes did not use their initial conditions optimally (Fig.1). The optimal energy decrease was calculated for the analyzed athletes as between 4 and 5 J/kg (Fig.1)

Effects of ankle–foot braces on medial gastrocnemius morphometrics and gait in children with cerebral palsy

Purpose In children with cerebral palsy (CP), braces are used to counteract progressive joint and muscle contracture and improve function. We examined the effects of positional ankle–foot braces on contracture of the medial gastrocnemius (MG) and gait in children with CP while referencing to typically developing children. Methods Seventeen independently ambulant children with CP and calf muscle contracture (age 10.4 ± 3.0y) and 17 untreated typically developing peers (age 9.5 ± 2.6y) participated. Children with CP were analysed before and 16 ± 4 weeks after ankle–foot bracing. MG muscle belly length and thickness, tendon and fascicle length, as well as their extensibility were captured by 2D ultrasound and 3D motion capturing during passive, manually applied stretches. In addition, 3D gait analysis was conducted. Results Prior to bracing, the MG muscle–tendon unit in children with CP was 22 % less extensible. At matched amounts of muscle–tendon unit stretch, the muscle belly and fascicles in CP were 7 % and 14 % shorter while the tendon was 11 % longer. Spastic fascicles displayed 32 % less extensibility than controls. Brace wear increased passive dorsiflexion primarily with the knees flexed. During gait, children walked faster and foot lift in swing improved. MG muscle belly and tendon length showed little change, but fascicles further shortened (−11 %) and muscle thickness (−8 %) decreased. Conclusions Use of ankle–foot braces improves function but may lead to a loss of sarcomeres in series, which could explain the shortened fascicles. To potentially induce gastrocnemius muscle growth, braces may also need to extend the knee or complementary training may be necessary to offset the immobilizing effects of braces.Peer Reviewe

Assessment and modelling of the activation‐dependent shift in optimal length of the human soleus muscle in vivo

Previous in vitro and in situ studies have reported a shift in optimal muscle fibre length for force generation (L0) towards longer length at decreasing activation levels (also referred to as length‐dependent activation), yet the relevance for in vivo human muscle contractions with a variable activation pattern remains largely unclear. By a combination of dynamometry, ultrasound and electromyography (EMG), we experimentally obtained muscle force–fascicle length curves of the human soleus at 100%, 60% and 30% EMGmax levels from 15 participants aiming to investigate activation‐dependent shifts in L0 in vivo. The results showed a significant increase in L0 of 6.5 ± 6.0% from 100% to 60% EMGmax and of 9.1 ± 7.2% from 100% to 30% EMGmax (both P < 0.001), respectively, providing evidence of a moderate in vivo activation dependence of the soleus force–length relationship. Based on the experimental results, an approximation model of an activation‐dependent force–length relationship was defined for each individual separately and for the collective data of all participants, both with sufficiently high accuracy (R2 of 0.899 ± 0.056 and R2 = 0.858). This individual approximation approach and the general approximation model outcome are freely accessible and may be used to integrate activation‐dependent shifts in L0 in experimental and musculoskeletal modelling studies to improve muscle force predictions.Deutsche Forschungsgemeinschaft DFG, German Research FoundationPeer Reviewe

CONTROL OF LEG STIFFNESS AND ITS EFFECT ON MECHANICAL ENERGETIC

INTRODUCTION: In normal daily activity as in sports, humans adjust their physical behavior depending on the ground surface characteristics (Farley et al., 1998; Ferris, Liang & Farley, 1999) by being able to vary their performance (Arampatzis, 1999; Sanders, 1993). A difference in surface stiffness leads to a change in leg stiffness (Farley et al., 1998; Ferris, Liang & Farley, 1999). There are published results on relationships between joint stiffness and oxygen consumption (Dalleau et al., 1998; Heise & Martin, 1993). From this research, it can be concluded that leg stiffness influences athletic performance. The relationship between leg stiffness and performance during explosive movements on a sprung surface has not been reported in the literature to date. Leg Stiffness can be influenced by stride frequency while running (Farley & Gonzalez, 1996) or hopping frequency when bouncing in place (Farley & Morgenroth, 1999). These findings support the idea that it is possible to control leg stiffness by manipulating ground contact times and to consider its effects on mechanical energetic processes during drop jumps on a sprung surface. The purpose of this study is two-fold: a. Examinations of the effect of verbal instructions, given to the subjects for the control of lower -extremity stiffness. b. Assessment of the effect of the leg stiffness on mechanical energetic processes during drop jumps on a sprung surface

Muscle and Tendon Morphology in Early-Adolescent Athletes and Untrained Peers

Adolescent athletes can feature significantly greater muscle strength and tendon stiffness compared to untrained peers. However, to date, it is widely unclear if radial muscle and tendon hypertrophy may contribute to loading-induced adaptation at this stage of maturation. The present study compares the morphology of the vastus lateralis (VL) and the patellar tendon between early-adolescent athletes and untrained peers. In 14 male elite athletes (A) and 10 untrained controls (UC; 12–14 years of age), the VL was reconstructed from full muscle segmentations of magnetic resonance imaging (MRI) sequences and ultrasound imaging was used to measure VL fascicle length and pennation angle. The physiological cross-sectional area (PCSA) of the VL was calculated by dividing muscle volume by fascicle length. The cross-sectional area (CSA) of the patellar tendon was measured over its length based on MRI segmentations as well. Considering body mass as covariate in the analysis, there were no significant differences between groups considering the VL anatomical cross-sectional area (ACSA) over its length or maximum ACSA (UC: 24.0 ± 8.3 cm2, A: 28.1 ± 5.3 cm2, p > 0.05), yet athletes had significantly greater VL volume (UC: 440 ± 147 cm3, A: 589 ± 121 cm3), PCSA (UC: 31 ± 9 cm2, A: 46 ± 9 cm2), pennation angle (UC: 8.2 ± 1.4°, A: 10.1 ± 1.3°), and average patellar tendon CSA (UC: 1.01 ± 0.18 cm2, A: 1.21 ± 0.18 cm2) compared to the untrained peers (p < 0.05). However, the ratio of average tendon CSA to VL PCSA was significantly lower in athletes (UC: 3.4 ± 0.1%, A: 2.7 ± 0.5%; p < 0.05). When inferring effects of athletic training based on the observed differences between groups, these results suggest that both muscle and tendon of the knee extensors respond to athletic training with radial growth. However, the effect seems to be stronger in the muscle compared to the tendon, with an increase of pennation angle contributing to the marked increase of muscle PCSA. A disproportionate response to athletic training might be associated with imbalances of muscle strength and tendon stiffness and could have implications for the disposition towards tendon overuse injury.Peer Reviewe

Comparing the Effects of Two Perturbation-Based Balance Training Paradigms in Fall-Prone Older Adults: A Randomized Controlled Trial

Introduction: There is increasing evidence that perturbation-based balance training (PBT) is highly effective in preventing falls at older age. Different PBT paradigms have been presented so far, yet a systematic comparison of PBT approaches with respect to feasibility and effectiveness is missing. Two different paradigms of PBT seem to be promising for clinical implementation: (1) technology-supported training on a perturbation treadmill (PBTtreadmill); (2) training of dynamic stability mechanisms in the presence of perturbations induced by unstable surfaces (PBTstability). This study aimed to compare both program's feasibility and effectiveness in fall-prone older adults. Methods: In this three-armed randomized controlled trial, seventy-one older adults (74.9 ± 6.0 years) with a verified fall risk were randomly assigned into three groups: PBTtreadmill on a motorized treadmill, PBTstability using unstable conditions such as balance pads, and a passive control group (CG). In both intervention groups, participants conducted a 6-week intervention with 3 sessions per week. Effects were assessed in fall risk (Brief-BEST), balance ability (Stepping Threshold Test, center of pressure, limits of stability), leg strength capacity, functional performance (Timed Up and Go Test, Chair-Stand), gait (preferred walking speed), and fear of falling (Short FES-I). Results: Fifty-one participants completed the study. Training adherence was 91% for PBTtreadmill and 87% for PBTstability, while no severe adverse events occurred. An analysis of covariance with an intention-to-treat approach revealed statistically significant group effects in favor of PBTstability in the Brief-BEST (p = 0.009, η2 = 0.131) and the limits of stability (p = 0.020, η2 = 0.110) and in favor of PBTtreadmill in the Stepping Threshold Test (p < 0.001, η2 = 0.395). The other outcomes demonstrated no significant group effects. Conclusion: Both training paradigms demonstrated high feasibility and were effective in improving specific motor performances in the fall-prone population and these effects were task specific. PBTtreadmill showed higher improvements in reactive balance, which might have been promoted by the unpredictable nature of the included perturbations and the similarity to the tested surface perturbation paradigm. PBTstability showed more wide-ranging effects on balance ability. Consequently, both paradigms improved fall risk-associated measures. The advantages of both formats should be evaluated in light of individual needs and preferences. Larger studies are needed to investigate the effects of these paradigms on real-life fall rates.This study was supported by the Klaus Tschira Foundation. The responsibility for the content of this paper lies with the authors. The funders did not take any part in this work.Peer Reviewe