Effects of repeated ankle stretching on calf muscle-tendon and ankle biomechanical properties in stroke survivors

Background

The objective of this study was to investigate changes in active and passive biomechanical properties of the calf muscle–tendon unit induced by controlled ankle stretching in stroke survivors.

Methods

Ten stroke survivors with ankle spasticity/contracture and ten healthy control subjects received intervention of 60-min ankle stretching. Joint biomechanical properties including resistance torque, stiffness and index of hysteresis were evaluated pre- and post-intervention. Achilles tendon length was measured using ultrasonography. The force output of the triceps surae muscles was characterized via the torque–angle relationship, by stimulating the calf muscles at a controlled intensity across different ankle positions.

Findings

Compared to healthy controls, the ankle position corresponding to the peak torque of the stroke survivors was shifted towards plantar flexion (P < 0.001). Stroke survivors showed significantly higher resistance torques and joint stiffness (P < 0.05), and these higher resistances were reduced significantly after the stretching intervention, especially in dorsiflexion (P = 0.013). Stretching significantly improved the force output of the impaired calf muscles in stroke survivors under matched stimulations (P < 0.05). Ankle range of motion was also increased by stretching (P < 0.001).

Interpretation

At the joint level, repeated stretching loosened the ankle joint with increased passive joint range of motion and decreased joint stiffness. At the muscle–tendon level, repeated stretching improved calf muscle force output, which might be associated with decreased muscle fascicle stiffness, increased fascicle length and shortening of the Achilles tendon. The study provided evidence of improvement in muscle tendon properties through stretching intervention.     

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 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.     

Use of MRI for volume estimation of tibialis posterior and plantar intrinsic foot muscles in healthy and chronic plantar fasciitis limbs

Background

Due to complexity of the plantar intrinsic foot muscles, little is known about their muscle architecture in vivo. Chronic plantar fasciitis may be accompanied by muscle atrophy of plantar intrinsic foot muscles and tibialis posterior compromising the dynamic support of the foot prolonging the injury. Magnetic resonance images of the foot may be digitized to quantify muscle architecture. The first purpose of this study was to estimate in vivo the volume and distribution of healthy plantar intrinsic foot muscles. The second purpose was to determine whether chronic plantar fasciitis is accompanied by atrophy of plantar intrinsic foot muscles and tibialis posterior.

Methods

Magnetic resonance images were taken bilaterally in eight subjects with unilateral plantar fasciitis. Muscle perimeters were digitally outlined and muscle signal intensity thresholds were determined for each image for volume computation.

Findings

The mean volume of contractile tissue in healthy plantar intrinsic foot muscles was 113.3 cm³. Forefoot volumes of plantar fasciitis plantar intrinsic foot muscles were 5.2% smaller than healthy feet (P = 0.03, ES = 0.26), but rearfoot (P = 0.26, ES = 0.08) and total foot volumes (P = 0.07) were similar. No differences were observed in tibialis posterior size.

Interpretations

While the total volume of plantar intrinsic foot muscles was similar in healthy and plantar fasciitis feet, atrophy of the forefoot plantar intrinsic foot muscles may contribute to plantar fasciitis by destabilizing the medial longitudinal arch. These results suggest that magnetic resonance imaging measures may be useful in understanding the etiology and rehabilitation of chronic plantar fasciitis.     

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.     

Relationship of knee shear force and extensor moment on knee translations in females performing drop landings: a biplane fluoroscopy study

Background

Research has linked knee extensor moment and knee shear force to the non-contact anterior cruciate ligament injury during the landing motion. However, how these biomechanical performance factors relate to knee translations in vivo is not known as knee translations cannot be obtained with traditional motion capture techniques. The purpose of this study was to combine traditional motion capture with high-speed, biplane fluoroscopy imaging to determine relationships between knee extensor moment and knee shear force profiles with anterior and lateral tibial translations occurring during drop landing in female athletes.

Methods

15 females performed drop landings from a height of 40 cm while being recorded using a high speed, biplane fluoroscopy system and simultaneously being recorded using surface marker motion capture techniques to estimate knee joint angle, reaction force and moment profiles.

Findings

No significant statistical relationships were observed between peak anterior or posterior knee shear force and peak anterior and lateral tibial translations; or, between peak knee extensor moment and peak anterior and lateral tibial translations. Although differences were noted in peak shear force (P = 0.02) and peak knee extensor moment (P < 0.001) after stratification into low and high shear force and moment cohorts, no differences were noted in anterior and lateral tibial translations (all P ≥ 0.18).

Interpretation

Females exhibiting high knee extensor moment and knee shear force during drop landings do not yield correspondingly high anterior and lateral tibial translations.     

Effects of the index finger position and force production on the flexor digitorum superficialis moment arms at the metacarpophalangeal joints - a magnetic resonance imaging study

Background

The purpose of this study was to use magnetic resonance imaging to measure the moment arm of the flexor digitorum superficialis tendon about the metacarpophalangeal joint of the index, middle, ring, and little fingers when the position and force production level of the index finger was altered. A secondary goal was to create regression models using anthropometric data to predict moment arms of the flexor digitorum superficialis about the metacarpophalangeal joint of each finger.

Methods

The hands of subjects were scanned using a 3.0 T magnetic resonance imaging scanner. The metacarpophalangeal joint of the index finger was placed in: flexion, neutral, and extension. For each joint configuration subjects produced no active force (passive condition) and exerted a flexion force to resist a load at the fingertip (active condition).

Results

The following was found: (1) The moment arm of the flexor digitorum superficialis at the metacarpophalangeal joint of the index finger (a) increased with the joint flexion and stayed unchanged with finger extension; and (b) decreased with the increase of force at the neutral and extended finger postures and did not change at the flexed posture. (2) The moment arms of the flexor digitorum superficialis tendon of the middle, ring, and little fingers (a) did not change when the index metacarpophalangeal joint position changed (P > 0.20); and (b) The moment arms of the middle and little fingers increased when the index finger actively produced force at the flexed metacarpophalangeal joint posture. (4) The moment arms showed a high correlation with anthropometric measurements.

Interpretation

Moment arms of the flexor digitorum superficialis change due to both changes in joint angle and muscle activation; they scale with various anthropometric measures.     

Greater Q angle may not be a risk factor of patellofemoral pain syndrome

Background

A greater Q-angle has been suggested as a risk factor for Patellofemoral Pain Syndrome. Greater frontal plane knee moment and impulse have been found to play a functional role in the onset of Patellofemoral Pain Syndrome in a running population. Therefore, the purpose of this investigation was to determine the relationship between Q-angle and the magnitude of knee abduction moment and impulse during running.

Methods

Q-angle was statically measured, using a goniometer from three markers on the anterior superior iliac spine, the midpoint of the patella and the tibial tuberosity. Thirty-one recreational runners (21 males and 10 females) performed 8–10 trials running at 4 m/s (SD 0.2) on a 30 m-runway. Absolute and normalized knee moment and impulse were calculated and correlated with Q-angle.

Findings

Negative correlations between Q-angle and the magnitude of peak knee abduction moment (R² = 0.2444, R = − 0.4944, P = 0.005) and impulse (R² = 0.2563, R = − 0.5063, P = 0.004) were found. Additionally, negative correlations between Q-angle and the magnitude of weight normalized knee abduction moment (R² = 0.1842, R = − 0.4292, P = 0.016) and impulse (R² = 0.2304, R = − 0.4801, P = 0.006) were found.

Interpretation

The findings indicate that greater Q-angle, which is actually associated with decreased frontal plane knee abduction moment and impulse during running, may not be a risk factor of Patellofemoral Pain Syndrome.     

Alterations in in vivo knee joint kinematics following a femoral nerve branch block of the vastus medialis: Implications for patellofemoral pain syndrome

Background

A potential source of patellofemoral pain, one of the most common problems of the knee, is believed to be altered patellofemoral kinematics due to a force imbalance around the knee. Although no definitive etiology for this imbalance has been found, a weak vastus medialis is considered a primary factor. Therefore, this study's purpose was to determine how the loss of vastus medialis obliquus force alters three-dimensional in vivo knee joint kinematics during a volitional extension task.

Methods

Eighteen asymptomatic female subjects with no history of knee pain or pathology participated in this IRB approved study. Patellofemoral and tibiofemoral kinematics were derived from velocity data acquired using dynamic cine-phase contrast MRI. The same kinematics were then acquired immediately after administering a motor branch block to the vastus medialis obliquus using 3–5 ml of 1% lidocaine. A repeated measures analysis of variance was used to test the null hypothesis that the post- and pre-injection kinematics were no different.

Findings

The null hypothesis was rejected for patellofemoral lateral shift (P = 0.003, max change = 1.8 mm, standard deviation = 1.7 mm), tibiofemoral lateral shift (P < 0.001, max change = 2.1 mm, standard deviation = 2.9 mm), and tibiofemoral external rotation (P < 0.001, max change = 3.7°, standard deviation = 4.4°).

Interpretation

The loss of vastus medialis obliquus function produced kinematic changes that mirrored the axial plane kinematics seen in individuals with patellofemoral pain, but could not account for the full extent of these changes. Thus, vastus medialis weakness is likely a major factor in, but not the sole source of, altered patellofemoral kinematics in such individuals.     

Influences of hamstring stiffness and strength on anterior knee joint stability

Background

Excessive anterior tibial translation is a prospective risk factor for anterior cruciate ligament injury, thus factors which limit this motion may reduce injury risk. Stiffness quantifies a muscle's resistance to lengthening, and stiffer hamstrings may resist changes in length induced by anterior tibial translation more effectively.

Methods

Anterior tibial translation, hamstring strength, and hamstring stiffness were assessed in 30 physically active volunteers. Simple correlations were used to evaluate relationships between stiffness, strength, and anterior tibial translation. Anterior tibial translation data were arranged into high and low groups based on the median value, and hamstring strength and stiffness were compared between these groups via t-tests.

Findings

Anterior tibial translation was correlated with hamstring stiffness (r = −0.538; P = 0.002), but not with hamstring strength (r = −0.088; P = 0.644). Hamstring stiffness and strength were not correlated (r = 0.054; P = 0.778). Hamstring stiffness was greater in the low anterior tibial translation group (t₂₈ = 2.186; P < 0.037; ES = 0.36), but hamstring strength did not differ between these groups (t₂₈ = 1.057; P < 0.300; ES = 0.17).

Interpretation

Greater hamstring stiffness, but not strength, results in a more stable knee joint evidenced by less anterior tibial translation. These findings suggest that the hamstrings’ ability to resist lengthening rather than their overall force production capacity may be an important contributor to anterior cruciate ligament injury risk. As muscle stiffness can be modified acutely and chronically, enhancing hamstring stiffness may be an important addition to anterior cruciate ligament injury prevention programs.