Effects of stretch speed, muscular contraction, and psychological state on ankle dorsiflexion maximum range of motion and stiffness
Camila D. Lima
Date of Award
Thesis - ECU Access Only
Edith Cowan University
Doctor of Philosophy
School of Medical and Health Sciences
Joint flexibility can be defined as the maximum range of motion (ROMmax.) that can be achieved or as the magnitude of resistance to the stretch itself. It may be influenced by mechanical features of the joint and the stretched muscle-tendon unit (MTU) as well as the response from muscle and tendon sensory receptors. The sensory signals act via afferent pathways to elicit reflexive activity and also travel to the brain where interpretation of this information might affect the ‘decision’ to resist further stretch. However, the influence of different biological factors that acutely affect ROMmax and the resistance to stretch (i.e., joint stiffness) is not fully understood. The primary purpose of the research presented within the present thesis was to examine the relative importance of several biological factors (e.g., joint stiffness, reflexive activity, and psychological state) on acute alterations in joint stiffness and ROMmax during dorsiflexion rotations (plantar flexor muscle stretches). A second purpose was to understand how different conditions of stretch speed and muscle contraction during stretch interact with these biological factors.
This thesis comprised three experimental studies. The aim of the first study was to examine the effects of both stretch rate and psychological state (e.g., arousal state) on ROMmax, stiffness, and muscle activity (electromyogram amplitude; EMG) during passive ankle dorsiflexions. Seventeen females were tested for their ROMmax and ankle (joint) stiffness in aroused (positive music) , control (no music), or relaxed (calm music) mental states, as induced by listening to specific musical scores. They perfomed four familiarisation ankle stretches (2 slow [5°/s] and 2 fast [30°/s]) before performing the stretches under six randomised conditions (control, arousal, and relaxation conditions at slow and fast speeds). ROMmax was not different between conditions but greater ROMmax was produced at the faster stretch speed overall, despite being accompanied by higher gastrocnemius medialis (GM) and soleus (SOL) EMG activities. 2 Joint stiffness was greater near to ROMmax, but no effect of psychological state was observed. Muscle activity onset occurred closer to ROMmax at slower than faster speeds for both muscles. The greater ROMmax achieved in faster stretches indicates the capacity for significant joint ranges of motion to be attained as we move at faster speeds, despite the greater resistive muscle activity. The lack of effect of arousal state (n = 13) suggests that such interventions may not substantially alter decision making with respect to ROMmax and may thus not be a successful method of acutely altering ROMmax.
In the second study, the effects of psychological state (aroused vs. relaxed vs. control) on H-reflex amplitudes were assessed in fourteen flexible females. Testing was performed in a randomised order under different psychological states (as described in Study 1) and during a stretch with stimuli triggered when the plantar flexors were at a short length (15° plantarflexion) and when they were at a long length (at 90% ROMmax) in a separate and random order. H (H- reflex) and M (M-wave) maximum amplitudes were determined from full recruitment curves (~20 stimuli) for the first condition. After determining these amplitudes, a ‘reduced’ recruitment curve (~ 5 to 10 stimuli) was captured for each condition and position. No statistical interaction or main effects were detected for any of the variables (Hmax, H:M ratio and Mmax) between arousal conditions or joint positions. The data suggest that arousal state may not strongly influence excitability of the H-reflex pathway, which might at least partly explain its lack of effect in Study 1.
The aim of the third study was to examine the effect of agonist (plantarflexors active) and antagonist (dorsiflexors active) muscle activation during plantarflexor stretches on ROMmax and EMG activity. Seventeen females first performed MVCs of the plantar flexors then dorsiflexors while the ankle joint was rotated to ROMmax. Subsequently, two stretches to ROMmax were performed under each muscle contraction condition (plantarflexors active, dorsiflexors active, no voluntary activation [control]) in a random order, with active conditions requiring the participants to produce a torque of 60% MVC through the full range of motion. EMG signals were obtained from GM and SOL during the stretches. ROMmax was less in the dorsiflexors active than plantarflexors active or control conditions, while plantarflexor peak and mean EMG activities were greater with plantarflexors active than dorsiflexors active and control conditions. Therefore, dorsiflexor activation, which should speculatively induce reciprocal inhibition onto the plantarflexors during the stretch, did not reduce plantar flexor activity (compared to control) nor improve ROMmax (in fact, it decreased). Further, activation of the plantarflexors, which significantly increases the muscles’ resistance to stretch, did not reduce ROMmax. Therefore, there appears to be no clear rationale for maintaining relaxed agonist muscles, at least during slow- speed calf muscle stretches.
In conclusion, the findings of the research presented in this thesis indicate that ROMmax could be easily achieved along with high joint stiffness and muscle activity in faster stretches and those with the agonist muscle active, without detectable influence of arousal state. Stretches at faster speeds in fact increased ROMmax despite increases in both joint stiffness and muscle activity when compared to slow speeds, whilst stretches with the agonist muscles active allow for the same ROMmax to be achieved as in traditional, slow-speed, relaxed (passive) tests. However, activity of the Ia afferent pathway, assessed by the H-reflex during stretch, demonstrated little effect on ROMmax. Therefore, acute alterations in joint stiffness and ROMmax may be influenced by stretch speed and the amount of muscle activity (EMG), especially under faster stretch speed conditions, which might provide sensory feedback during the stretch. Collectively, these studies advance our understanding of factors and conditions that might affect acute improvements in joint flexibility.
Access to this thesis is embargoed until 14th November 2028.
de Paula de Lima, C. (2023). Effects of stretch speed, muscular contraction, and psychological state on ankle dorsiflexion maximum range of motion and stiffness. Edith Cowan University. https://doi.org/10.25958/fm83-zs21