Tendon Moment Arm Research Articles

The effect of biceps reattachment site

We hypothesize that an anatomic repair of the distal biceps tendon would recreate native tendon moment arm and forearm rotation, while a nonanatomic insertion would compromise moment arm and forearm rotation. Isometric supination torque was measured at 60° of pronation, neutral, and 60° of supination for the native distal biceps tendon and 4 repair points in 6 cadaveric specimens using a computer controlled elbow simulator. The slope of the regression line fitted to the torque versus biceps load data was used to define the moment arm for each attachment location. Range of motion testing was performed by incrementally loading the biceps, while measuring the supination motion generated using a digital goniometer. Tendon location and forearm position significantly affected the moment arm of the biceps (P < .05). Anatomic repair in all forearm positions showed no significant difference from the native insertion. Moment arm for an anterior center repair was significantly lower in supination (-97%) and neutral (-27%) and also produced significantly less supination motion. No difference was observed between all tendon locations in pronation. Reattachment of the biceps to its anatomic location, as opposed to a more anterior central position, is critical in reestablishing native tendon biomechanics. Clinically, these findings would suggest that patients with a biceps repair might experience the most weakness in a supinated position without experiencing a deficit in the pronated forearm.

Direct comparison of in vivo Achilles tendon moment arms obtained from ultrasound and MR scans

Accurate and reliable estimation of muscle moment arms is a prerequisite for the development of musculoskeletal models. Numerous techniques are available to estimate the Achilles tendon moment arm in vivo. The purposes of this study were 1) to compare in vivo Achilles tendon moment arms obtained using the center of rotation (COR) and tendon excursion (TE) methods and 2) to assess the reliability of each method. For the COR method, magnetic resonance (MR) images from nine participants were obtained at ankle angles of -15°, 0°, and +15° and analyzed using Reuleaux' method. For the TE method, the movement of the gastrocnemius medialis-Achilles tendon junction was recorded using ultrasonography as the ankle was passively rotated through its range of motion. The Achilles tendon moment arm was obtained by differentiation of tendon displacement with respect to ankle angular excursion using seven different differentiation techniques. Moment arms obtained using the COR method were significantly greater than those obtained using the TE method (P < 0.01), but results from both methods were well correlated. The coefficient of determination between moment arms derived from the COR and TE methods was highest when tendon displacement was linearly differentiated over a ± 10° interval (R(2) = 0.94). The between-measurement coefficient of variation was 3.9% for the COR method and 4.5-9.7% for the TE method, depending on the differentiation technique. The high reliabilities and strong relationship between methods demonstrate that both methods are robust against their limitations. The large absolute between-method differences (∼ 25-30%) in moment arms have significant implications for their use in musculoskeletal models.

Inter-individual variability in the adaptation of human muscle specific tension to progressive resistance training

Considerable variation exists between people in the muscle response to resistance training, but there are numerous ways muscle might adapt to overload that might explain this variable response. Therefore, the aim of this study was to quantify the range of responses concerning the training-induced change in maximum voluntary contraction (MVC) knee joint torque, quadriceps femoris (QF) maximum muscle force (F), physiological cross-sectional area (PCSA) and specific tension (F/PCSA). It was hypothesized that the variable change in QF specific tension between individuals would be less than that of MVC. Fifty-three untrained young men performed progressive leg-extension training three times a week for 9weeks. F was determined from MVC torque, voluntary muscle activation level, antagonist muscle co-activation and patellar tendon moment arm. QF specific tension was established by dividing F by QF PCSA, which was calculated from the ratio of QF muscle volume to muscle fascicle length. MVC torque increased by 26±11% (P<0.0001; range -1 to 52%), while F increased by 22±11% (P<0.0001; range -1 to 44%). PCSA increased by 6±4% (P<0.001; range -3 to 18%) and specific tension increased by 17±11% (P<0.0001; range -5 to 39%). In conclusion, training-induced changes in F and PCSA varied substantially between individuals, giving rise to greater inter-individual variability in the specific tension response compared to that of MVC. Furthermore, it appears that the change in specific tension is responsible for the variable change in MVC.

A Hybrid Method for Computing Achilles Tendon Moment Arm Using Ultrasound and Motion Analysis

In this article, we outline a method for computing Achilles tendon moment arm. The moment arm is computed from data collected using two reliable measurement instruments: ultrasound and video-based motion capture. Ultrasound is used to measure the perpendicular distance from the surface of the skin to the midline of the tendon. Motion capture is used to determine the perpendicular distance from the bottom of the probe to the ankle joint center. The difference between these two measures is the Achilles tendon moment arm. Unlike other methods, which require an angular change in joint position to approximate the moment arm, the hybrid method can be used to compute the moment arm directly at a specific joint angle. As a result, the hybrid method involves fewer error-prone measurements and the moment arm can be computed at the limits of the joint range of motion. The method is easy to implement and uses modalities that are less costly and more accessible than MRI. Preliminary testing using a lamb shank as a surrogate for a human ankle revealed good accuracy (3.3% error). We believe the hybrid method outlined here can be used to measure subject-specific moment arms in vivo and thus will potentially benefit research projects investigating ankle mechanics.

Mechanical properties of the patellar tendon in adults and children

It is not currently known how the mechanical properties of human tendons change with maturation in the two sexes. To address this, the stiffness and Young's modulus of the patellar tendon were measured in men, women, boys and girls (each group, n=10). Patellar tendon force ( F pt) was calculated from the measured joint moment during a ramped voluntary isometric knee extension contraction, the antagonist knee extensor muscle co-activation quantified from its electromyographical activity, and the patellar tendon moment arm measured from magnetic resonance images. Tendon elongation was imaged using the sagittal-plane ultrasound scans throughout the contraction. Tendon cross-sectional area was measured at rest from ultrasound scans in the transverse plane. Maximal F pt and tendon elongation were (mean±SE) 5453±307 N and 5±0.5 mm for men, 3877±307 N and 4.9±0.6 mm for women, 2017±170 N and 6.2±0.5 mm for boys and 2169±182 N and 5.9±0.7 mm for girls. In all groups, tendon stiffness and Young's modulus were examined at the level that corresponded to the maximal 30% of the weakest participant's F pt and stress, respectively; these were 925–1321 N and 11.5–16.5 MPa, respectively. Stiffness was 94% greater in men than boys and 84% greater in women than girls ( p<0.01), with no differences between men and women, or boys and girls (men 1076±87 N/mm; women 1030±139 N/mm; boys 555±71 N/mm and girls 561.5±57.4 N/mm). Young's modulus was 99% greater in men than boys ( p<0.01), and 66% greater in women than girls ( p<0.05). There were no differences in modulus between men and women, or boys and girls (men 597±49 MPa; women 549±70 MPa; boys 255±42 MPa and girls 302±33 MPa). These findings indicate that the mechanical stiffness of tendon increases with maturation due to an increased Young's modulus and, in females due to a greater increase in tendon cross-sectional area than tendon length.

In vivo measurements of muscle specific tension in adults and children

To better understand the effects of pubertal maturation on the contractile properties of skeletal muscle in vivo, the present study investigated whether there are any differences in the specific tension of the quadriceps muscle in 20 adults and 20 prepubertal children of both sexes. Specific tension was calculated as the ratio between the quadriceps tendon force and the sum of the physiological cross-sectional area (PCSA) multiplied by the cosine of the angle of pennation of each head within the quadriceps muscle. The maximal quadriceps tendon force was calculated from the knee extension maximal voluntary contraction (MVC) by accounting for EMG-based estimates of antagonist co-activation, incomplete quadriceps activation using the interpolation twitch technique and magnetic resonance imaging (MRI)-based measurements of the patellar tendon moment arm. The PCSA was calculated as the muscle volume, measured from MRI scans, divided by optimal fascicle length, measured from ultrasound images during MVC at the estimated angle of peak quadriceps muscle force. It was found that the quadriceps tendon force and PCSA of men (11.4 kN, 214 cm(2)) were significantly greater than those of the women (8.7 kN, 152 cm(2); P < 0.01). Both adult groups had greater values than the children (P < 0.01) but there were no differences between boys (5.2 kN, 99 cm(2)) and girls (6.1 kN, 102 cm(2)). Agonist activation was greater in men and women than in girls (P < 0.05), and antagonist activation was greater in men than in boys (P < 0.05). Moment arm length was greater in men than in boys or girls and greater in women than in boys (P < 0.05). The angle of pennation did not differ between the groups in any of the quadriceps heads. The specific tension was similar (P > 0.05) between groups: men, 55 +/- 11 N cm(-2); women, 57.3 +/- 13 N cm(-2); boys, 54 +/- 14 N cm(-2); and girls, 59.8 +/- 15 N cm(-2). These findings indicate that the increased muscle strength with maturation is not due to an increase in the specific tension of muscle; instead, it can be attributed to increases in muscle size, moment arm length and voluntary activation level.

Built for speed: musculoskeletal structure and sprinting ability

The musculoskeletal structure of the foot and ankle has the potential to influence human sprinting performance in complex ways. A large Achilles' tendon moment arm improves the mechanical advantage of the triceps surae but also produces larger shortening velocity during rapid plantarflexion, which detracts from the force-generating capacity of the plantarflexors. The lever arm of the ground reaction force that resists the muscular plantarflexor moment during propulsive push-off is constrained in part by the skeletal structure of the foot. In this study, we measured the plantarflexion moment arms of the Achilles' tendon, lateral gastrocnemius fascicle lengths and pennation angles, and anthropometric characteristics of the foot and lower leg in collegiate sprinters and height-matched non-sprinters. The Achilles' tendon moment arms of the sprinters were 25% smaller on average in sprinters than in non-sprinters (P<0.001) whereas the sprinters' fascicles were 11% longer on average (P=0.024). The ratio of fascicle length to moment arm was 50% larger in sprinters (P<0.001). Sprinters were found to have longer toes (P=0.032) and shorter lower legs (P=0.026) than non sprinters. A simple computer simulation of the sprint push-off demonstrated that shorter plantarflexor moment arms and longer toes, like those measured in sprinters, permit greater generation of forward impulse. Simulated propulsion was enhanced in both cases by increasing the ;gear ratio' of the foot, thus maintaining plantarflexor fibre length and reducing peak fibre shortening velocity. Longer toes especially prolonged the time of contact, giving greater time for forward acceleration by propulsive ground reaction force.

Moment arms of the knee extensor mechanism in children and adults

In the present study we investigated whether there are differences in the patellar tendon moment arm (PTMA)-knee angle relationship between pre-pubertal children and adults, and whether the PTMA length scales to relevant anthropometric measurements in the two groups. Anthropometric characteristics and the PTMA length-joint angle relationships were determined in 20 adults and 20 pre-pubertal children of both genders. The anthropometric characteristics measured were height, body mass, knee circumference, medio-lateral knee breadth, anterior-posterior knee depth, leg length, femur length and tibia length. The PTMA was quantified from magnetic resonance images using the geometric centre of the femoral condyle method, at every 5 degrees between 55 degrees and 90 degrees of knee flexion (0 degrees is full extension). Adults had a significantly greater PTMA length at all joint angles (4.2 +/- 0.4 vs. 3.6 +/- 0.3 cm at 90 degrees ; P < 0.01), with the PTMA length decreasing from knee extension to knee flexion similarly in both adults and children. There were no significant and strong correlations between the PTMA and anthropometric measures in adults for any joint angle. In contrast, the PTMA correlated and scaled with anthropometric characteristics for the children (P < 0.05, r = 0.49-0.9) at all joint angles. The PTMA length in children was most accurately predicted at 85 degrees of flexion from the equation PTMA = -0.25 + 0.083 x tibia length + 0.02 x leg length (R(2) = 0.83). These findings indicate that the knee extensor mechanism in pre-pubertal children should not be considered to be a 'scaled-down' version of that in adults.

Comparison of tendon tensions estimated from two biomechanical models of the thumb

Despite the paramount function of the thumb in daily life, thumb biomechanical models have been little developed and studied. Moreover, only two studies provided quantitative anthropometric data of tendon moment arms. To investigate thumb tendon tensions, biomechanicians and clinicians have to know the performances and the limits of these two data sets. The aim of this study was thus to compare the results of these two models and evaluate their performances in regard to prior electromyographic measurements (EMG). Thumb posture was recorded during the classical key pinch and pulp pinch grips. Various fingertip forces applied at the distal segment were simulated in a range including extension, adduction, flexion, abduction. Input data of thumb postures and fingertip forces were used to compute tendon tensions with both models. Tendon tensions obtained using these two models were then compared and correlated to EMG measurements provided in the literature. The results showed that both models predicted relevant muscle coordination for five of the nine muscles modelled. Opponent and abductor longus muscle coordinations were badly estimated by both models. Each model was sensible to kinematic errors but not in the same proportion. This study pointed out the advantages/limits of the two models to use them more appropriately for clinical and/or research purposes.

Effect of acute tensile loading on gender‐specific tendon structural and mechanical properties

Stretching is commonly used prior to exercise, as it is thought to reduce the risk of injury, and it is also used in the preconditioning of tendon grafts. As tendon properties have been shown to be different between genders, it is proposed that stretching will differentially affect the structure. Here we examine the effect of acute stretch on the mechanical properties of both male and female medial gastrocnemius tendon. Female [20 years +/- 1 (SEM), n = 17] and male (22 years +/- 1, n = 18) subjects underwent a 5-min passive dorsiflexion stretch. Prior to and post stretch medial gastrocnemius tendon stiffness (K), length (l) and cross-sectional area (csa) were measured using ultrasonography and dynamometry. Stiffness and Young's modulus (epsilon) were significantly reduced with stretch for both genders (p < 0.05). Females showed significantly (p < 0.05) greater pre- to poststretch decreases in K (22.4 vs. 8.8%) and epsilon (20.5 vs. 8.4%) in comparison to males. The present results show that stretching acutely reduces stiffness of the medial gastrocnemius tendon in females and males, with females showing significantly greater change. The observed disparity between genders may be due in part to variations in tendon moment arm and intrinsic differences in tendon composition. These differential changes in tendon mechanical properties have functional, motor control, and injury risk implications, as well as possible implications for preconditioning of tendon grafts.

A comparison of different two-dimensional approaches for the determination of the patellar tendon moment arm length

The purpose of this study was to estimate and compare the moment arm length of the patellar tendon (d) during passive knee extension using three different reference landmarks; instant centre of rotation (ICR), tibiofemoral contact point (TFCP) and geometrical centre of the posterior femoral condyles (GCFC). Measurements were taken on the right leg on seven healthy males during passive knee rotation performed by the motor of a Cybex Norm isokinetic dynamometer. Moment arms lengths were obtained by analysing lateral X-ray images recorded using a GE FlexiView 8800 C-arm videofluoroscopy system. The d-knee joint angle relations with respect to GCFC and ICR were similar, with decreasing values from full knee extension (~5.8 cm for d (GCFC) and ~5.9 cm for d (ICR)) to 90 degrees of knee flexion (~4.8 cm for both d (GCFC) and d (ICR)). However, the d (TFCP)-knee joint angle relation had an ascending-descending shape, with the highest d (TFCP) value (~5 cm) at 60 degrees of knee flexion. There was no significant difference between the GCFC and ICR methods at any knee joint angle. In contrast, there were significant differences (P < 0.01) between d (ICR) and d (TFCP) at 0 degrees , 15 degrees , 30 degrees and 45 degrees of knee flexion and between d (GCFC) and d (TFCP) at 0 degrees , 15 degrees and 30 degrees of knee flexion (P < 0.01). This study shows that when using different knee joint rotation centre definitions, there are significant differences in the estimates of the patellar tendon moment arm length, especially in more extended knee joint positions. These differences can have serious implications for joint modelling and loading applications.

Running biomechanics: shorter heels, better economy

Better running economy (i.e. a lower rate of energy consumption at a given speed) is correlated with superior distance running performance. There is substantial variation in running economy, even among elite runners. This variation might be due to variation in the storage and reutilization of elastic energy in tendons. Using a simple musculoskeletal model, it was predicted that the amount of energy stored in a tendon during a given movement depends more critically on moment arm than on mechanical properties of the tendon, with the amount of stored energy increasing as the moment arm gets smaller. Assuming a link between elastic energy reutilization and overall metabolic cost of running, a smaller moment arm should therefore be associated with superior running economy. This prediction was confirmed experimentally in a group of 15 highly trained runners. The moment arm of the Achilles tendon was determined from standardized photographs of the ankle, using the position of anatomical landmarks. Running economy was measured as the rate of metabolic energy consumption during level treadmill running at a speed of 16 km h(-1). A strong correlation was found between the moment arm of the Achilles tendon and running economy. Smaller muscle moment arms correlated with lower rates of metabolic energy consumption (r(2)=0.75, P<0.001).

Effects of knee joint angle on the fascicle behavior of the gastrocnemius muscle during eccentric plantar flexions

The present study aimed to clarify the effects of knee joint angle on the behavior of the medial gastrocnemius muscle (MG) fascicles during eccentric plantar flexions. Eight male subjects performed maximal eccentric plantar flexions at two knee positions [fully extended (K0) and 90° flexed (K90)]. The eccentric actions were preceded by static plantar flexion at a 30° plantar flexed position and then the ankle joint was forcibly dorsiflexed to 15° of dorsiflexion with an isokinetic dynamometer at 30°/s and 150°/s. Tendon force was calculated by dividing the plantar flexion torque by the estimated moment arm of the Achilles tendon. The MG fascicle length was determined with ultrasonography. The tendon forces during eccentric plantar flexions were influenced by the knee joint angle, but not by the angular velocity. The MG fascicle lengths were elongated as the ankle was dorsiflexed in K0, but in K90 they were almost constant despite the identical range of ankle joint motion. These results suggested that MG fascicle behavior during eccentric actions was markedly affected by the knee joint angle. The difference in the fascicle behavior between K0 and K90 could be attributed to the non-linear force–length relations and/or to the slackness of tendinous tissues.

Three-dimensional In Vivo Quantification of Knee Kinematics in Cerebral Palsy

Cerebral palsy is the most common disabling condition in childhood, involving a diverse group of movement and posture disorders of varying etiologies. Yet, much is unknown about how cerebral palsy affects individual joints because currently applied techniques cannot quantify the three-dimensional kinematic parameters at the joint level. We quantified the effects of cerebral palsy at the knee using fast phase contrast MRI, with the ultimate intent of improving the assessment of joint impairments associated with cerebral palsy, improving clinical outcomes, and reducing the impact of cerebral palsy on function. We addressed three questions: (1) Can patients with cerebral palsy perform the required repetitive extension task? (2) Which of the 12 degrees of freedom defining complete knee kinematics are abnormal in individual patients with cerebral palsy and is the patellar tendon moment arm abnormal in these patients? (3) Are the individual kinematic differences consistent with clinical observations? All patients were able to perform the required task. We found kinematic differences for each patient with cerebral palsy consistent with clinical findings, in comparison to an able-bodied population. Fast phase contrast MRI may allow differentiation of patellofemoral and tibiofemoral function in various functional subtypes of cerebral palsy, providing insights into its management.

In vivo quantification of the Achilles tendon moment arm

The Achilles' tendon moment arm (ATma) is a critical quantity in that it defines the triceps surea's ability to generate a moment on the calcaneus, which is then transferred to the foot. In the past this measure has been primarily acquired statistically, in 2D, without muscle activation, and in small populations. Thus, the primary purpose of this study was to establish the first in vivo three-dimensional measures of the ATma, measured non-invasively and in vivo during dynamic activity in a large normative population (n = 19) using a dynamic MRI technique. The ATma was defined as the shortest distance between the finite helical axis (FHA) of the calcaneal-tibial joint and the AT line of action.

Biomechanical Analysis of Distal Biceps Tendon Repair Methods

Background The 1-incision and 2-incision techniques are commonly used methods to repair a distal biceps rupture, and they differ in the location of reinsertion of tendon into bone. Hypothesis The native distal biceps brachii tendon inserts on the posterior-ulnar aspect of the bicipital tuberosity, which functions as a cam, increasing the tendon's moment arm during its principal action of forearm supination. Repair of the distal biceps tendon to the anterior aspect of the tuberosity compromises forearm supination due to absence of the bicipital tuberosity's cam effect. Study Design Controlled laboratory study. Methods Eleven matched pairs of fresh-frozen cadaveric upper extremities were prepared for repair of the distal biceps tendon using either anterior or posterior reattachment with transosseous suture fixation. Specimens were tested on a materials testing machine with intact distal biceps insertion and after repair. A load cell at the distal radial-ulnar joint measured resultant elbow flexion and forearm supination torque produced by 100-N force applied to the proximal aspect of the tendon. Results Although there was a trend (P = .104) toward loss of supination torque with the anterior reconstruction method, no significant differences in torque (0.80 vs 0.89 N·m) or flexion force (11.87 vs 12.07 N) were found between the anterior and posterior reconstruction techniques. Conclusion There is no statistically significant difference in flexion force or supination torque between the anterior and posterior reconstruction techniques. Clinical Relevance This study supports existing limited clinical data suggesting no functional differences exist between 2 common repair methods. Further biomechanical and clinical investigations directly comparing the results of distal biceps tendon repairs made to the anterior aspect versus the posterior aspect of the tuberosity are necessary to definitely determine if differences exist in resultant elbow flexion and forearm supination functions.

In vivo changes in the human patellar tendon moment arm length with different modes and intensities of muscle contraction

The purpose of this study was to examine the effect of different muscle contraction modes and intensities on patellar tendon moment arm length ( d PT ) . Five men performed isokinetic concentric, eccentric and passive knee extensions at an angular velocity of 60 deg/s and six men performed gradually increasing to maximum effort isometric muscle contractions at 90 ∘ and 20 ∘ of knee flexion. During the tests, lateral X-ray fluoroscopy imaging was used to scan the knee joint. The d PT differences between the passive state and the isokinetic concentric and extension were quantified at 15 ∘ intervals of knee joint flexion angle. Furthermore, the changes of the d PT as a function of the isometric muscle contraction intensities were determined during the isometric knee extension at 90 ∘ and 20 ∘ of knee joint flexion. Muscle contraction-induced changes in knee joint flexion angle during the isometric muscle contraction were also taken into account for the d PT measurements. During the two isometric knee extensions, d PT increased from rest to maximum voluntary muscle contraction (MVC) by 14–15%. However, when changes in knee joint flexion angle induced by the muscle contraction were taken into account, d PT during MVC increased by 6–26% compared with rest. Moreover, d PT increased during concentric and eccentric knee extension by 3–15%, depending on knee flexion angle, compared with passive knee extension. These findings have important implications for estimating musculoskeletal loads using modelling under static and dynamic conditions.

The 3D patellar tendon moment arm: Quantified in vivo during volitional activity

The patellar tendon moment arm is a critical quantity in that it defines the quadriceps ability to generate a moment on the tibia. Thus, the primary purpose of this study was to establish the first in vivo three-dimensional measures of the patellar tendon moment arm, measured non-invasively and in vivo during dynamic activity in a large normative population ( n=34) using a dynamic MRI technique (fast-PC MRI). The magnitude of the moment arm was defined as the shortest distance between the finite helical axis and the patellar tendon line of action. Using these data, the hypothesis that the patellar tendon moment arm is independent of gender was tested. In general, the moment arm increased from 20 to 50 mm during knee extension. There were significant differences ( P<0.05) in the moment arm between gender, but these differences were eliminated when the moment arm was scaled by the femoral epicondylar width. This study took a large step forward towards the ultimate goal of defining how pathology may alter joint dynamics through alteration in moment arms by establishing the first in vivo normative data base for the patellar tendon moment arm using non-invasive measures during volitional activity in a relatively large population ( n=34). The fact that the scaled moment arm was independent of gender may lend insights into impairments that tend to be gender specific, such as patellar maltracking. The next steps will be to quantify the patellar tendon moment arm in populations with specific pathologies.

Gastrocnemius specific force is increased in elderly males following a 12-month physical training programme

The aim of the present investigation was to determine whether muscle force per physiological cross sectional area (PCSA) of the lateral gastrocnemius (GL) of elderly males increased following a 12-month physical training programme. Eleven elderly males were assigned to a 12-month training programme (TRN mean age 72.7 +/- 3.3 years, mean +/- SD) and eight elderly males were allocated to a control group (CTRL, 73.9 +/- 4.0 years) who maintained their habitual physical activity levels. In vivo measurements of muscle architecture, muscle volume (VOL), achilles tendon moment arm length and plantarflexor torque were used to estimate GL PCSA (VOL/fascicle length) and specific force (GL fascicle force/GL PCSA). Maximal GL fascicle force was calculated accounting for agonist muscle activation and antagonist co-activation. Following training GL fascicle force increased by 31% (P < 0.01), which was not entirely accounted for by a 17% increase in PCSA (from 27.2 +/- 5.9 to 31.8 +/- 6.2 cm(2), P < 0.05). Specific force increased significantly from 8.9 +/- 1.9 to 11.2 +/- 3.0 N cm(-2) (P < 0.05). Pennation angle, but not fascicle length, increased by 12% with training (P < 0.05). The CTRL group showed no change in muscle size, strength or architecture over the 12-month period. In conclusion, with the level of agonist and antagonist muscle activity accounted for a 12-month strength training programme resulted in an increase in both PCSA and specific force in elderly males.

Neuromuscular and Isometric Force-velocity Adaptations to Concentric and Eccentric Strength Training

PURPOSE: To examine the mechanisms underpinning a velocity-specific strength increase after slow-speed concentric or eccentric knee extensor (KE) training, we assessed neuromuscular adaptations to isometric KE contractions performed with and without a maximum rate of force development. METHODS: 10 men and 11 women with no history of resistance training performed 10 wk (3.wk−1) of either eccentric or concentric, isokinetic KE training through 90° at 30o.s−1. Before and after training, concentric and eccentric dynamic KE moment was measured at 30 and 180°.s−1. Also, isometric KE moment was measured in trials with a maximum rate of force development (fast) and in a ramped contraction reaching peak moment after 5 s (slow). EMG was recorded from the superficial quadriceps femoris (QF) and biceps femoris (BF) muscles. Antagonist torque during isometric KE was estimated from the EMG-torque relationship measured during a ramped isometric knee flexion (KF) contraction; KE torque was calculated as the sum of KE moment and KF torque−1. QF volume and patella tendon moment arm were measured from magnetic resonance imaging scans. QF force was calculated as the ratio of KE torque-to-moment arm. RESULTS: Isometric KE moment was greater in fast trials (pre-training: fast = 176.1 ± 44.4 Nm, slow = 147.5 ± 52.9 Nm), which was due to a greater QF muscle force (16.4%) with no difference in BF torque (i.e. decreased KF:KE ratio). Mean QF EMG was greater in fast trials, although differences in individual muscles did not reach significance. After training, isometric force increased in both fast (16.8 Nm, 9.5%) and slow (22.2 Nm, 15.1%) trials in both groups, with the greater increase in slow force mirroring the dynamic force changes (all subjects Δ30°s−1 = 44.1 Nm; Δ180°s−1 = 24.7 Nm). Decreases in KF torque accounted for some of the increase in isometric moment in fast (10.9 Nm, 64.9% of change) and slow (8.9 Nm, 40.1% of change) trials. Despite an increase in QF volume (9.6%; no difference between groups) and a trend toward an increase in average QF EMG in the slow isometric trials (p=0.06; increase in rectus femoris EMG, p <0.05; trend toward increased vastus medialis EMG, p=0.08), training-related increases in isometric QF force or KE torque did not reach statistical significance. CONCLUSIONS: The increased isometric KE moment after slow-speed KE training was greater in trials performed with a slow rate of force development, and was associated with a reduced KF torque with a non-significant increase in KE torque. Proportional increases in dynamic moment were greater than isometric, so larger increases in KE contribution in dynamic movements cannot be ruled out.