Influence of overweight on the active and the passive fraction of the plantar flexors series elastic component in prepubertal children

Abstract

The influence of overweight, as a precursor to obesity, was analyzed on the elastic properties of the triceps surae. Based on body mass index (BMI), children (9 years ± 4 mo) were classified as control (CON; n = 23; BMI -1SD>Z score<1SD) or overweight (OW; n = 21, BMI 1SD>Z score<3SD) with regard to reference data from the World Health Organization. Musculotendinous (MT) stiffness of the series elastic component (SEC) was determined using quick-release tests to obtain 1) the MT stiffness index from the slope of either linear stiffness-torque (SI(MT-Torque)) or stiffness-EMG (SI(MT-EMG)) relationships and 2) passive stiffness from the intercept point with the ordinate. Finally, the SEC active (α(0)) and passive fractions (C(passive)) were separated as described by Morgan (Am J Physiol, 1977), using alpha-torque (α(0-Torque,) C(passive-Torque)) or alpha-EMG (α(0-EMG,) C(passive-EMG)) relationships. No significant differences in SI(MT-Torque) or α(0-Torque) were observed between OW and CON. SI(MT-EMG) or α(0-EMG) values were significantly different between OW and CON, which indicate an increase in MT stiffness. In all cases, passive stiffness (K(p), C(passive-torque), C(passive-EMG)) was significantly greater in OW but independent of the activation capacities. These results indicate that a weight-related additional loading of the MT structures in OW children caused the MT system to response accordingly to the functional demand, i.e., higher stiffness of the MT structures due to a concomitant increase in the stiffness of the SEC passive and active fraction. This study also reveals that possible differences in the activation capacities influence the determination of MT stiffness of the SEC active fraction.

Interaction between gastrocnemius medialis fascicle and Achilles tendon compliance: a new insight on the quick-release method

“…The statistical difference observed for the first 5-ms window should be considered with caution because the contribution was quantified for very small shortenings (Ͻ2-3 mm) of the tissues. The technique used here may be compared with the ␣-method (47) that has recently been adapted in vivo to estimate the stiffness of the active and passive part of the SEE of plantar flexors (9,17,19,44,58). This last method is mainly indirect because it calculates the stiffness of each part of the SEEs on the basis of only mechanical data (joint angle and external torque) and a model.…”

“…To measure its compliance in humans, classical methods were adapted from isolated muscle techniques such as quick-release (QR), controlled-release, or short-range stretching methods. For instance, numerous studies have used QR to investigate changes in musculotendinous stiffness induced by training programs (26,50), immobilization (43) or neuromuscular diseases (10,11), or to compare musculotendinous stiffness between different populations (41,44,52,53). This QR method consists of a sudden and fast release of the isometrically contracted muscle, as a "catapult-like" movement, using a specific ergometer (42,59).…”

Relationship between obesity and musculoskeletal system findings among children and adolescents

“…On the other hand, some differences have been reported between overweight/obese children and normal weight children in several studies. Lambertz et al [15] measured strength of triceps surae muscle using electromyography and reported an increased strength in obese children compared to normal weight children. Ervin et al [16] assessed muscle strength by observing children during a structured exercise program and they reported decreased performance in obese children in weight-bearing movements.…”

To pull or be pulled: parsing the multiple modes of mechanotransduction

“…During physical activity, muscle cells must maintain tissue integrity while still exerting forces on their surrounding environment. On short timescales, muscles have an intrinsic stiffness that resists deformation, but also can isometrically contract to stiffen if needed [71]. Activity triggers long-term gene expression [72], allowing cells to adapt by growing bigger and changing their contractile ability in anticipation of future activity.…”