Biomechanical properties of the triceps surae muscle-tendon unit in young and postmenopausal women

Background

Insufficient and excessive stiffness may increase the risk of soft tissue and bone injuries, respectively, while the resonance frequency seems to be related with energy expenditure and stiffness. With aging and menopause muscle weakness, physical fragility and mobility limitations are also expected. Therefore this study addresses the differences of biomechanical properties of the triceps surae muscle–tendon unit between young and postmenopausal women.

Methods

39 young and 37 postmenopausal women participated. The biomechanical properties of the triceps surae muscle–tendon unit were assessed in vivo using a free oscillation technique involving 30% of the maximal voluntary isometric contraction load.

Findings

The postmenopausal women in this study show significant higher values in the damped natural frequency of oscillation (young 3.84 Hz vs. postmenopausal 4.68 Hz, P < 0.001), muscle–tendon unit stiffness (young 16,446 N/m vs. postmenopausal 23,229 N/m, P < 0.001), and muscle–tendon unit stiffness normalized by mass (young 286.3 N/m vs. postmenopausal 325.1 N/m, P < 0.05). The postmenopausal study group shows significant lower values in the damping ratio (young 0.190 vs. postmenopausal 0.150, P < 0.01) than young women.

Interpretation

The postmenopausal subjects may not be able to take advantage of resonance as the young subjects, or, the relationship between these frequencies is adjusted according to the musculoskeletal characteristics of each group. The decrease in damping properties and the increase in muscle–tendon unit stiffness suggest that postmenopausal women might be at a greater risk of injury.     

The contribution of quasi-joint stiffness of the ankle joint to gait in patients with hemiparesis

Background

The role of ankle joint stiffness during gait in patients with hemiparesis has not been clarified. The purpose of this study was to determine the contribution of quasi-joint stiffness of the ankle joint to spatiotemporal and kinetic parameters regarding gait in patients with hemiparesis due to brain tumor or stroke and healthy individuals.

Methods

Spatiotemporal and kinetic parameters regarding gait in twelve patients with hemiparesis due to brain tumor or stroke and nine healthy individuals were measured with a 3-dimensional motion analysis system. Quasi-joint stiffness was calculated from the slope of the linear regression of the moment–angle curve of the ankle joint during the second rocker.

Findings

There was no significant difference in quasi-joint stiffness among both sides of patients and the right side of controls. Quasi-joint stiffness on the paretic side of patients with hemiparesis positively correlated with maximal ankle power (r = 0.73, P < 0.01) and gait speed (r = 0.66, P < 0.05). In contrast, quasi-joint stiffness in controls negatively correlated with maximal ankle power (r = − 0.73, P < 0.05) and gait speed (r = − 0.76, P < 0.05).

Interpretation

Our findings suggested that ankle power during gait might be generated by increasing quasi-joint stiffness in patients with hemiparesis. In contrast, healthy individuals might decrease quasi-joint stiffness to avoid deceleration of forward tilt of the tibia. Our findings might be useful for selecting treatment for increased ankle stiffness due to contracture and spasticity in patients with hemiparesis.     

Triceps-surae musculotendinous stiffness: Relative differences between obese and non-obese postmenopausal women

Background

There is a lack of research into the relationship between obesity and muscle–tendon unit stiffness in postmenopausal women. Muscle–tendon unit stiffness appears to affect human motion performance and excessive and insufficient stiffness can increase the risk of bone and soft tissue injuries, respectively. The aim of this study was to investigate the relationship between muscle–tendon unit stiffness and obesity in postmenopausal women.

Methods

105 postmenopausal women (58 [SD 5.5] years) participated. Four groups (normal weight, pre-obese, obesity class I and obesity class II) were defined according World Health Organization classification of body mass index. The ankle muscle–tendon unit stiffness was assessed in vivo with a free oscillation technique using a load of 30% of maximal voluntary isometric contraction.

Findings

ANOVA shows significant difference in muscle–tendon unit stiffness among the groups defined (P < 0.001). Post hoc analysis reveals significant differences between the following groups: normal weight–pre-obese; normal weight–obesity class I and normal weight–obesity class II. The normal weight group had stiffness of 15789 (SD 2969) N/m, pre-obese of 19971 (SD 3678) N/m, obesity class I of 21435 (SD 4295) N/m, and obesity class II of 23497 (SD 1776) N/m.

Interpretation

Obese subjects may have increased muscle–tendon unit stiffness because of fat infiltration in leg skeletal muscles, range of motion restrictions and stability/posture reasons and might be more predisposed to develop musculoskeletal injuries. Normal weight group had identical stiffness values to those reported in studies where subjects were not yet menopausal, suggesting that stiffness might not be influenced by menopause.     

Lack of effect of moderate-duration static stretching on plantar flexor force production and series compliance

Background

The effects of an acute bout of moderate-duration static stretching on plantar flexor force production, series compliance of the muscle–tendon unit, and levels of neuromuscular activation were examined.

Methods

Eighteen active individuals (9 men and 9 women) performed four 45-s static plantar flexor stretches and a time-matched control of no stretch (where subjects remained seated in the dynamometer for 4 min with no stretch being performed). Measures of peak isometric moment, rate of force development, neuromuscular activation (interpolated twitch technique and electromyography), twitch force characteristics, passive moment during stretch, and tendon elongation during maximal voluntary contractions were taken before and after the stretching.

Findings

Despite a significant stress–relaxation response during stretch (9.3%, P < 0.01) there were no significant differences in peak isometric moment (P = 0.35; effect size 0.13), rate of force development (P = 0.93; effect size 0.01), neuromuscular activation (interpolated twitch: P = 0.86; electromyography: P = 0.09; effect size 0.02), or tendon elongation (P = 0.61; effect size 0.07) after stretching. Twitch characteristics were also unchanged after stretching, although there was a reduction in the rate of twitch torque relaxation (RR_t; P < 0.01).

Interpretation

The acute bout of moderate-duration static stretching did not impair the force generating capacity of the plantar flexors or negatively affect muscle–tendon mechanical properties. Static stretching may not always have detrimental consequences for force production. Thus, clinicians may be able to apply moderate-duration stretches to patients without risk of reducing muscular performance.     

Changes in Passive Mechanical Properties of the Gastrocnemius Muscle at the Muscle Fascicle and Joint Levels in Stroke Survivors

Gao F, Grant TH, Roth EJ, Zhang L-Q. Changes in passive mechanical properties of the gastrocnemius muscle at the muscle fascicle and joint levels in stroke survivors.

Objectives

To investigate the ankle joint-level and muscle fascicle-level changes and their correlations in stroke survivors with spasticity, contracture, and/or muscle weakness at the ankle.

Design

To investigate the fascicular changes of the medial gastrocnemius muscle using ultrasonography and the biomechanical changes at the ankle joint across 0°, 30°, 60°, and 90° knee flexion in a case-control manner.

Setting

Research laboratory in a rehabilitation hospital.

Participants

Stroke survivors (n=10) with ankle spasticity/contracture and healthy control subjects (n=10).

Interventions

Not applicable.

Main Outcome Measurements

At the muscle fascicle level, medial gastrocnemius muscle architecture including the fascicular length, pennation angle, and thickness were evaluated in vivo with the knee and ankle flexion changed systematically. At the joint level, the ankle range of motion (ROM) and stiffness were determined across the range of 0° to 90° knee flexion.

Results

At comparable joint positions, stroke survivors showed reduced muscle fascicle length, especially in ankle dorsiflexion (P≤.048) and smaller pennation angle, especially for more extended knee positions (P≤.049) than those of healthy control subjects. At comparable passive gastrocnemius force, stroke survivors showed higher fascicular stiffness (P≤.044) and shorter fascicle length (P≤.025) than controls. The fascicle-level changes of decreased muscle fascicle length and pennation angle and increased medial gastrocnemius fascicle stiffness in stroke were correlated with the joint level changes of increased joint stiffness and decreased ROM (P<.05).

Conclusions

This study evaluated specific muscle fascicular changes as mechanisms underlying spasticity, contracture, and joint-level impairments, which may help improve stroke rehabilitation and outcome evaluation.     

The effects of immobilization on the mechanical properties of the patellar tendon in younger and older men

Background

It remains unknown if inactivity changes the mechanical properties of the human patellar tendon in younger and older healthy persons. The purpose was to examine the effects of short-term unilateral immobilization on the structural and mechanical properties of the patellar tendon in older men and younger men, in vivo.

Methods

Eight older men and eight younger men underwent 14 days of unilateral immobilization. All individuals were assessed on both sides before and after the intervention. MRI was used to assess whole patellar tendon dimensions. The mechanical properties of the patellar tendon were assessed using simultaneous force and ultrasonographic measurements during isometric ramp contractions.

Findings

In older men, tendon stiffness [Pre: mean 2949 (SD 799) vs. Post: mean 2366 (SD 774) N mm^− 1, P < 0.01] and Young's Modulus [Pre: mean 1.2 (SD 0.3) vs. Post: mean 1.0 (SD 0.3) GPa, P < 0.05] declined with immobilization on the immobilized side. On the control side, tendon stiffness [Pre: mean 3340 (SD 1209) vs. Post: mean 2230 (SD 503), P < 0.01] and Young's Modulus [Pre: mean 1.5 (SD 0.4) vs. Post: mean 0.9 (SD 0.3) GPa, P < 0.05] also decreased with immobilization. In younger men, tendon stiffness [Pre: 3622 (SD 1760) vs. Post: mean 2910 (SD 1528) N mm^− 1, P < 0.01] and Young's Modulus [Pre: mean 1.7 (SD 1.1) vs. Post: mean 1.4 (SD 0.8) GPa, P < 0.05] decreased only on the immobilized side.

Interpretation

Short-term immobilization led to impaired mechanical properties of the patellar tendon on the immobilized side in both younger men and older men, which can influence the function of the muscle–tendon complex.     

Increased power generation in impaired lower extremities correlated with changes in walking speeds in sub-acute stroke patients

Background

Establishing changes in net joint power in the lower extremity of patients during recovery of walking might direct gait training in early stroke rehabilitation. It is hypothesized that (1) net joint power in the lower extremity joints would increase in sub-acute stroke patients following gait rehabilitation, and (2) the improvements in net joint power would be significantly correlated with changes in walking speed.

Methods

Thirteen sub-acute patients (<3 months from stroke onset) participated in the study. All patients completed 6 weeks of gait training (3 weeks of robotic gait training and 3 weeks of physiotherapy). The gait patterns were analyzed using 3D motion analysis before and after training. The assessed variables were; gait speed and the net peak joint power of the ankle plantar flexors, hip extensors, hip flexors, hip abductors, and knee extensors.

Findings

Ankle plantar flexor power in the impaired limb and hip extensor power in the unimpaired limb increased significantly following training (133% and 77%, respectively; P < 0.002). Improvements (from 20% to 133%) in net joint power of the ankle plantar flexors, hip extensors, hip flexors, and hip abductors of the impaired limb and ankle plantar flexors and hip abductors of the unimpaired limb significantly correlated with the recovery of walking speed following training (0.24 m/s to 0.51 m/s) (r = 0.71–0.86).

Interpretation

The findings suggested investigations for strengthening the plantar flexors, hip flexors, hip extensors, and hip abductors concentrically, and knee extensors eccentrically in the impaired limb to determine the effectiveness in improving gait performance.     

Dynamic hip joint stiffness in individuals with total hip arthroplasty: relationships between hip impairments and dynamics of the other joints

Background

Little is known about hip joint stiffness during walking (dynamic joint stiffness) and the effect of hip impairments on biomechanical alterations of other joints in patients with total hip arthroplasty.

Methods

Twenty-four patients (mean age 61.7 years) who underwent unilateral (n = 12) or bilateral total hip arthroplasty (n = 12) and healthy subjects (n = 12) were recruited. In addition to kinematic and kinetic variables, dynamic hip joint stiffness which was calculated as an angular coefficient of linear regression of the plot of the hip flexion moment vs. hip extension angle during the late stance of gait, was measured. Group differences were compared using one-way ANOVA and Tukey's post-hoc test, and relationships between primary hip impairments and secondary gait impairments were found using partial correlation coefficients adjusted for gait speed and stride length.

Findings

Dynamic hip joint stiffness was 47% higher on the side with the more pronounced limp in patients with bilateral arthroplasty than in healthy controls. In the same patients, increased dynamic hip joint stiffness was significantly associated especially with increased ankle plantarflexion moment on the ipsilateral side. In patients with unilateral arthroplasty, decreased hip power was significantly related to increased ankle plantarflexor power, only on the non-operated side.

Interpretation

We found that dynamic hip joint stiffness was an important factor in assessing relationships between hip impairments and dynamics in other joints, especially in patients with bilateral total hip arthroplasty. The effects of altering hip joint stiffness on gait biomechanics need to be explored.     

Impact of ankle osteoarthritis on the energetics and mechanics of gait: the case of hemophilic arthropathy

Background

Osteoarthritis may affect joints in any part of the body, including the ankle. The purpose of this study was to assess the impact of ankle osteoarthritis on the energetics and mechanics of gait, while taking into account the effect of slower speed generally adopted by patients with osteoarthritis.

Methods

Using a motion analysis system, synchronous kinematic, kinetics, spatiotemporal, mechanics and metabolic gait parameters were measured in 10 patients diagnosed with ankle osteoarthritis consecutive to hemophilia. The subjects walked at a self-selected speed and their performance was compared to speed-matched normal values obtained in healthy control subjects.

Findings

Speed-normalization using a Z-score transformation showed a significant increase in metabolic cost (Z = 1.78; P = 0.006) and decrease in mechanical work (Z = − 0.97; P = 0.009). As a consequence, muscular efficiency also decreased (Z = − 0.97; P = 0.001). These changes were associated with a surprising efficacy of the pendular mechanism, i.e., an improved recovery index (Z = 0.97; P = 0.004).

Interpretation

Our findings suggest that patients with ankle osteoarthritis adopt a walking strategy which improves recovery through the pendular mechanism. This may be a compensatory mechanism in order to economize energy which would counterbalance the energy waste due to low muscle efficiency. These modifications are proportional to the impaired ankle function. Our data provides a quantitative baseline to better understand the dynamics of ankle osteoarthritis and determine the individual role that lower limb joints play in the multiple chronic joint affections.