Muscle-tendon mechanics and energetics during walking, running and jumping

In the human lower limb, muscles and tendon tend to interact in an efficient manner during common movements like walking, running and jumping. This pattern of interaction exploits the ability of muscles to produce forces efficiently at low shortening velocities, whilst tendons act as springs that help to store elastic energy during the contact phase, and return a large proportion of the energy in the pushoff phase. This pattern of muscletendon interaction can be disrupted in novel tasks or as a consequence of ageing or disease, resulting in a decrease in movement efficiency

Terrace Review, March, 26, 1986

The presence of mechanical linkages between synergistic muscles and their common tendons may distribute forces among the involved structures. We review studies, using humans and other animals, examining muscle and tendon interactions and discuss the hypothesis that connections between muscle bellies and within tendons may serve as a mechanism to distribute forces and mitigate peak stresses

Validity of traditional physical activity intensity calibration methods and the feasibility of self-paced walking and running on individualised calibration of physical activity intensity in children

There are no practical and valid methods for the assessment of individualised physical activity (PA) intensity in observational studies. Therefore, we investigated the validity of commonly used metabolic equivalent of tasks (METs) and predetermined PA intensity classification methods against individualised PA intensity classification in 35 children 7–11-years-of-age. Then, we studied validity of mean amplitude deviation (MAD) measured by accelerometry during self-paced walking and running in assessment of individualised PA intensity. Individualised moderate PA (MPA) was defined as V̇O2 ≥ 40% of V̇O2reserve and V̇O2 3–6 (or alternatively > 4–7) METs as MPA and > 6 (> 7) METs as VPA. Task intensities were classified according to previous calibration studies. MET-categories correctly identified 25.9–83.3% of light PA, 85.9–90.3% of MPA, and 56.7–82.2% of VPA. Task-specific categories correctly classified 53.7% of light PA, 90.6% of MPA, and 57.8% of VPA. MAD during self-paced walking discriminated MVPA from light PA (sensitivity = 67.4, specificity = 88.0) and MAD during self-paced running discriminated VPA from MPA (sensitivity = 78.8, specificity = 79.3). In conclusion, commonly used methods may misclassify PA intensity in children. MAD during self-paced running may provide a novel and practical method for determining individualised VPA intensity in children.Peer reviewe

CHARACTERISTICS OF THE PATELLAR TENDONS IN ANTERIOR CRUCIATE LIGAMENT INJURED ATHLETES

The purpose of this study was to demonstrate the characteristics of patellar tendons and the quadriceps strength of athletes with anterior cruciate ligament reconstruction (ACLR) throughout rehabilitation. Athletes of different sports (n=27) had both patellar tendons (PT) assessed with ultrasound tissue characterization (UTC) method, and bilateral isokinetic quadriceps strength quantified in intervals of 1.5 months over their rehabilitation period. Reduction in the quality of the involved PT was observed after ACLR surgery, with these values returning to baseline at approximately 7.5 months post surgery. The uninvolved PT displayed no significant differences. Despite the increase in quadriceps strength, no statistical relevance was observed. ACLR caused reduction in the quality of the involved PT which might be correlated with tendon symptoms during the rehabilitation

Slower Walking Speed in Older Men Improves Triceps Surae Force Generation Ability

Purpose Older adults walk slower than young adults, but it is not known why. Previous research suggests that ankle plantarflexors may have a crucial role in the reduction of walking speed. The purpose of this study was to investigate age-related differences in triceps surae muscle–tendon function during walking to further investigate the role of plantarflexors in the age-related reduction of walking speed. Methods Medial gastrocnemius and soleus muscle fascicle lengths were measured using ultrasound imaging during walking from 13 young (25 ± 4 yr) men at preferred walking speed and from 13 older (73 ± 5 yr) men at preferred speed and at the young men’s preferred speed. Muscle–tendon unit lengths were calculated from joint kinematics, and tendinous tissue lengths were calculated by subtracting muscle lengths from muscle–tendon unit lengths. In addition, ground reaction forces and electromyographic activity of medial gastrocnemius and soleus were measured. Results In both medial gastrocnemius and soleus, it was observed that at preferred walking speed, older men used a narrower muscle fascicle operating range and lower shortening velocity at the estimated time of triceps surae peak force generation compared with young men. Fascicles also accounted for a lower proportion of muscle–tendon unit length changes during the stance phase in older compared with young men. Significant differences in triceps surae muscle function were not observed between age groups when compared at matched walking speed. Conclusions In older men, walking at preferred speed allows triceps surae muscles to generate force with more favorable shortening velocity and to enhance use of tendinous tissue elasticity compared with walking at young men’s preferred speed. The results suggest that older men may prefer slower walking speeds to compensate for decreased plantarflexor strength

Revising the stretch reflex threshold method to measure stretch hyperreflexia in cerebral palsy

Peer reviewe

Tendon length estimates are influenced by tracking location

Purpose Measurement of medial gastrocnemius (MG) tendon length using ultrasonography (US) requires the muscle-tendon junction (MTJ) to be located. Previously, the MG MTJ has been tracked from different proximo-distal locations near the MTJ, which could influence estimates of tendon length change due to the different characteristics of the aponeurosis and tendon. We used US to evaluate the effect of tracking point location on MG MTJ displacement during maximal and submaximal (10, 20 and 30% of the non-injured maximal) isometric plantar flexion contractions. Methods Displacement behaviour of MTJ was tracked from (1) the exact MTJ; and (2) from an insertion point of a muscle fascicle on the aponeurosis 1.3 +/- 0.6 cm proximal to the MTJ, in both limbs of patients with unilateral Achilles tendon rupture (ATR) (n = 22, 4 females, 42 +/- 9 years, 177 +/- 9 cm, 79 +/- 10 kg). Results In the non-injured limb, displacement (1.3 +/- 0.5 cm vs. 1.1 +/- 0.6 cm) and strain (6.7 +/- 2.8% vs. 5.8 +/- 3.3%) during maximal voluntary contraction were larger when tracking a point on the aponeurosis than when tracking the MTJ (both p < 0.001). The same was true for all contraction levels, and both limbs. Conclusion Tracking a point on the aponeurosis consistently exaggerates estimates of tendon displacement, and the magnitude of this effect is contraction intensity-dependent. When quantifying displacement and strain of the Achilles tendon, the MTJ should be tracked directly, rather than tracking a surrogate point proximal to the MTJ. The latter method includes part of the aponeurosis, which due to its relative compliance, artificially increases estimates of MTJ displacement and strain

Associations between cardiorespiratory fitness, motor competence, and adiposity in children

We investigated the associations of motor competence (MC) with peak oxygen uptake (V.O-2peak), peak power output (W-max), and body fat percentage (BF%) and whether measures of cardiorespiratory fitness (CRF) modify the associations between MC and BF%. Altogether, 35 children (aged 7-11 years) in the CHIPASE Study and 297 in PANIC Study (aged 9-11 years) participated in the study. MC was assessed using KTK and modified Eurofit tests. V.O-2peak and W-max were measured by maximal exercise test on a cycle ergometer and scaled by lean mass (LM) or body mass (BM). BF% was assessed either by bioimpedance (CHIPASE) or DXA (PANIC). MC was not associated with V.O-2peak/LM (standardized regression coefficient beta = 0.073-0.188, P > .083). V.O-2peak/BM and W-max/LM and BM were positively associated with MC (beta = 0.158-0.610, P .381), was inversely associated with BF%. Furthermore, the associations of MC with BF% were not modified by CRF. These results suggest that the positive associations between MC and CRF scaled by BM are a function of adiposity and not peak aerobic power and that CRF is not modifying factor in the associations of MC and BF%.Peer reviewe

Exploration of muscle–tendon biomechanics one year after Achilles tendon rupture and the compensatory role of flexor hallucis longus

Achilles tendon (AT) rupture leads to long-term structural and functional impairments. Currently, the predictors of good recovery after rupture are poorly known. Thus, we aimed to explore the interconnections between structural, mechanical, and neuromuscular parameters and their associations with factors that could explain good recovery in patients with non-surgically treated AT rupture. A total of 35 patients with unilateral rupture (6 females) participated in this study. Muscle-tendon structural, mechanical, and neuromuscular parameters were measured 1-year after rupture. Interconnections between the inter-limb differences (Δ) were explored using partial correlations, followed by multivariable linear regression to find associations between the measured factors and the following markers that indicate good recovery: 1) tendon length, 2) tendon non-uniform displacement, and 3) flexor hallucis longus (FHL) normalized EMG amplitude difference between limbs. Δmedial gastrocnemius (MG) (β = −0.12, p = 0.007) and Δlateral gastrocnemius (β = −0.086, p = 0.030) subtendon lengths were associated with MG tendon Δstiffness. MG (β = 11.56, p = 0.003) and soleus (β = 2.18, p = 0.040) Δsubtendon lengths explained 48 % of variance in FHL EMG amplitude. Regression models for tendon length and non-uniform displacement were not significant. Smaller inter-limb differences in Achilles subtendon lengths were associated with smaller differences in the AT stiffness between limbs, and a smaller contribution of FHL muscle to the plantarflexion torque. In the injured limb, the increased contribution of FHL appears to partially counteract a smaller contribution from MG due to the elongated tendon, however the role of FHL should not be emphasized during rehabilitation to allow recovery of the TS muscles