Exploratory factor analysis for differentiating sensory and mechanical variables related to muscle-tendon unit elongation

Abstract

BackgroundStretching exercises are able to promote adaptations in the muscle-tendon unit (MTU), which can be tested through physiological and biomechanical variables. Identifying the key variables in MTU adaptations is crucial to improvements in training.ObjectiveTo perform an exploratory factor analysis (EFA) involving the variables often used to evaluate the response of the MTU to stretching exercises.MethodMaximum joint range of motion (ROMMAX), ROM at first sensation of stretching (FSTROM), peak torque (torqueMAX), passive stiffness, normalized stiffness, passive energy, and normalized energy were investigated in 36 participants during passive knee extension on an isokinetic dynamometer. Stiffness and energy values were normalized by the muscle cross-sectional area and their passive mode assured by monitoring the EMG activity.ResultsEFA revealed two major factors that explained 89.68% of the total variance: 53.13% was explained by the variables torqueMAX, passive stiffness, normalized stiffness, passive energy, and normalized energy, whereas the remaining 36.55% was explained by the variables ROMMAX and FSTROM.ConclusionThis result supports the literature wherein two main hypotheses (mechanical and sensory theories) have been suggested to describe the adaptations of the MTU to stretching exercises. Contrary to some studies, in the present investigation torqueMAX was significantly correlated with the variables of the mechanical theory rather than those of the sensory theory. Therefore, a new approach was proposed to explain the behavior of the torqueMAX during stretching exercises.

The Proprioceptive Neuromuscular Facilitation Reduces Isometric Strength in Apparently Health Women

“…According to our results, 30 seconds of stretching by PNF method is already enough to occasion sensibility decrease in muscular proprioceptors, tendinous and articular, as well as in nociceptors, that constitute fundamental mechanisms for protection and organization of structures related to human movement, such strength reduction after stretching in different insistence times can be, partially, explained by an autogenic inhibition and reciprocal inhibition caused by stretching due to Golgi tendon organs activation that can cause decrease in alpha motoneurons excitability. However, corroboring with Chagas et al [9], we recommend further studies involving the long-term effects of stretching using different stretching methods and neurophysiological variables. In summary, it was verified that acutely stretching method by PNF causes reduction on muscular isometric strength of muscles involved in manual grip.…”

Comparison of four local vibratory stimuli on mechanical and sensorial variables related to muscle‐tendon unit response

“…Although ROM MAX and TOR MAX present a positive moderate correlation ( r = .69, P < .001), the common variance relative to the factors influencing these variables was less than 50% ( r 2 x 100). Chagas et al found that ROM MAX and TOR MAX fitted to the sensory and mechanical theories, respectively, as described by Weppler and Magnusson . Therefore, the determination of these variables seems to be established by distinct aspects.…”

“…They passed independently by all experimental conditions randomized by drawing lots. Flexibility variables were measured during stretching maneuvers in a dynamometer isokinetic soon before and after intervention with different mechanical vibration stimulus configurations. All tests were performed by the same examiner at the same period of the day to standardize the effects of circadian rhythm …”

“…Flexibility variables measured were maximum ROM (ROM MAX ) and torque (TOR MAX ), and their respective values at the first sensation of tightness (FST ROM and FST TOR ), corresponding to the initial tension feeling in hamstrings muscles during stretching. Passive stiffness (PS) was calculated as the slope of the third portion of torque vs. ROM time‐series, trimmed at 80% of ROM MAX curve . Intraclass correlation coefficient (ICC 3.1 ) and standard error of measurement (SEM) found for these measures were as follows: 0.99 and 2.49° for ROM MAX ; 0.98 and 2.31 Nm for TOR MAX ; 0.99 and 2.81° for FST ROM ; 0.99 and 1.63 Nm for FST TOR ; 0.96 and 0.03 Nm/° for PS; respectively.…”

“…There are three described explanations for increased ROM after LV stimulus application: (a) vibration‐induced muscle relaxation, (b) tolerance changing to stretching, and (c) increased muscle blood flow and temperature . In order to meet those theories, an investigation should consider also other variables that can influence joint ROM, such as torque, stiffness, and subjective perception of stretching, thus increasing the understanding of MTU response to elongation . Even if the analysis of these mechanical and sensorial variables related to the MTU response to stretching exercises has been already done, to the best of our knowledge, no one did it in association to different vibratory stimuli.…”