Do relevant shear forces appear in isokinetic shoulder testing to be implemented in biomechanical models?

Isokinetic dynamometers measure joint torques about a single fixed rotational axis. Previous studies yet suggested that muscles produce both tangential and radial forces during a movement, so that the contact forces exerted to perform this movement are multidirectional. Then, isokinetic dynamometers might neglect the torque components about the two other Euclidean space axes. Our objective was to experimentally quantify the shear forces impact on the overall shoulder torque, by comparing the dynamometer torque to the torque computed from the contact forces at the hand and elbow. Ten healthy women performed isokinetic maximal internal/external concentric/eccentric shoulder rotation movements. The hand and elbow contact forces were measured using two six-axis force sensors. The main finding is that the contact forces at the hand were not purely tangential to the direction of the movement (effectiveness indexes from 0.26 ± 0.25 to 0.54 ± 0.20), such that the resulting shoulder torque computed from the two force sensors was three-dimensional. Therefore, the flexion and abduction components of the shoulder torque measured by the isokinetic dynamometer were significantly underestimated (up to 94.9%). These findings suggest that musculoskeletal models parameters should not be estimated without accounting for the torques about the three space axes.     

Characterizing upper limb muscle volume and strength in older adults: a comparison with young adults

Aging is associated with the loss of muscle volume (MV) and force leading to difficulties with activities of daily living. However, the relationship between upper limb MV and joint strength has not been characterized for older adults. Quantifying this relationship may help our understanding of the functional declines of the upper limb that older adults experience. Our objective was to assess the relationship between upper limb MV and maximal isometric joint moment-generating capacity (IJM) in a single cohort of healthy older adults (age ≥ 65 years) for 6 major functional groups (32 muscles). MV was determined from MRI for 18 participants (75.1±4.3 years). IJM at the shoulder (abduction/adduction), elbow (flexion/extension), and wrist (flexion/extension) was measured. MV and IJM measurements were compared to previous reports for young adults (28.6±4.5 years). On average older adults had 16.5% less total upper limb MV compared to young adults. Additionally, older adult wrist extensors composed a significantly increased percentage of upper limb MV. Older adult IJM was reduced across all joints, with significant differences for shoulder abductors (p<0.0001), adductors (p=0.01), and wrist flexors (p<0.0001). Young adults were strongest at the shoulder, which was not the case for older adults. In older adults, 40.6% of the variation in IJM was accounted for by MV changes (p≤0.027), compared to 81.0% in young adults. We conclude that for older adults, MV and IJM are, on average, reduced but the significant linear relationship between MV and IJM is maintained. These results suggest that older adult MV and IJM cannot be simply scaled from young adults.     

Active and passive contributions to joint kinetics during walking in older adults

The objectives of this study were to characterize the active and passive contributions to joint kinetics during walking in healthy young and older adults, and assess whether isokinetic ankle strength is associated with ankle power output during walking. Twenty healthy young (18–35 years) and 20 healthy older (65–85 years) adults participated in this study. We measured subject-specific passive-elastic joint moment–angle relationships in the lower extremity and tested maximum isokinetic ankle strength at 30 deg/s. Passive moment–angle relationships were used to estimate active and passive joint moment, power, and work quantities during walking at 80%, 100% and 120% of preferred walking speed. There were no significant differences in walking speed, step length, or cadence between the older and young adults. However, the older adults produced significantly more net positive work at the hip but less net positive work at the ankle at all walking speeds. Passive contributions to hip and ankle work did not significantly differ between groups, inferring that the older adults generated the additional hip work actively. Maximum isokinetic ankle strength was significantly less in the older adults, and correlated with peak positive plantar-flexor power at both the preferred and fast walking speeds. The results of this study suggest that age-related shifts in joint kinetics do not arise as a result of increased passive hip joint stiffness, but seem to be reflected in plantar-flexor weakness.     

Contractile and elastic ankle joint muscular properties in young and older adults

The purpose of this study was to investigate age-related differences in contractile and elastic properties of both dorsi- (DF) and plantarflexor (PF) muscles controlling the ankle joint in young and older adults. Experimental data were collected while twelve young and twelve older male and female participants performed maximal effort isometric and isovelocity contractions on a dynamometer. Equations were fit to the data to give torque-angle (Tθ) and torque-angular velocity (Tω) relations. Muscle series-elasticity was measured during ramped dynamometer contractions using ultrasonography to measure aponeurosis extension as a function of torque; second order polynomials were used to characterize the torque-extension (TΔL) relation. The results showed no age differences in DF maximal torque and none for female PF; however, older males had smaller maximal PF torques compared to young males. In both muscle groups and genders, older adults had decreased concentric force capabilities. Both DF and PF TΔL relations were more nonlinear in the older adults. Older PF, but not DF muscles, were stiffer compared to young. A simple antagonism model suggested age-related differences in Tθ and Tω relations would be magnified if antagonistic torque contributions were included. This assessment of static, dynamic, and elastic joint properties affords a comprehensive view of age-related modifications in muscle function. Although many clinical studies use maximal isometric strength as a marker of functional ability, the results demonstrate that there are also significant age-related modifications in ankle muscle dynamic and elastic properties.     

Bilateral impairments of shoulder abduction in chronic hemiparesis: Electromyographic patterns and isokinetic muscle performance

ObjectiveTo analyze electromyographic (EMG) patterns and isokinetic muscle performance of shoulder abduction movement in individuals who sustained a cerebrovascular accident (CVA).DesignTwenty-two individuals who sustained a CVA and 22 healthy subjects volunteered for EMG activity and isokinetic shoulder abduction assessments. EMG onset time, root mean square (RMS) for upper trapezius and deltoid muscles, as well as the isokinetic variables of peak torque, total work, average power and acceleration time were compared between limbs and groups.ResultsThe paretic side showed a different onset activation pattern in shoulder abduction, along with a lower RMS for both muscles (21.8 ± 13.4% of the maximal voluntary isometric contraction (MVIC) for the deltoid and 25.9 ± 15.3% MVIC for the upper trapezius, about 50% lower than the control group). The non-paretic side showed a delay in both muscles activation and a lower RMS for the deltoid (32.2 ± 13.7% MVIC, about 25% lower than the control group). Both sides of the group of individuals who sustained a CVA presented a significantly lower isokinetic performance compared to the control group (paretic side ～60% lower; non-paretic side ～35% lower).ConclusionsShoulder abduction muscle performance is impaired in both paretic and non-paretic limbs of individuals who sustained a CVA.     

Effects of age on human muscle torque, velocity, and power in two muscle groups.

The purpose of this study was to test the hypotheses that, under isovelocity conditions, older compared with young humans would 1). be slower to reach target velocity and 2). exhibit a downward shift in the torque-velocity and power-velocity relationships in the ankle dorsiflexor and knee extensor muscles. We studied 12 young (26 +/- 5 yr, 6 men/6 women) and 12 older (72 +/- 6 yr, 6 men/6 women) healthy adults during maximal voluntary concentric contractions at preset target velocities (dorsiflexion: 0-240 degrees /s; knee extension: 0-400 degrees /s) using an isokinetic dynamometer. The time to target velocity was longer in older subjects in the dorsiflexors and knee extensors (both P 相似文献   

Reliability of concentric and eccentric strength of hip abductor and adductor muscles in young soccer players

The concentric and eccentric strength profile and muscular balance of the hip joint are important parameters for success in soccer. This study evaluated the reliability for the assessment of hip abduction and adduction isokinetic strength over a range of angular velocities (30 and 90°/s) and types of muscular actions (concentric and eccentric) in young soccer players. The reliability for the assessment of reciprocal (conventional and functional) and bilateral torque ratios was also examined. Fifteen male soccer players (15±1 years) performed two sessions, separated by three days. The testing protocol consisted of five maximal concentric and eccentric hip abductions and adductions of both legs at angular velocities of 30°/s and 90°/s. The peak torque was evaluated in young soccer players using an isokinetic dynamometer (Cybex Norm), and the reciprocal strength ratios (conventional and functional) and bilateral ratios (non-preferred to preferred leg ratios) were calculated. The test-retest reliability for the assessment of peak torque (ICC = 0.71-0.92) and of reciprocal muscle group ratios (ICC = 0.44-0.87) was found to be moderate to high. Bilateral torque ratios exhibited low to moderate reliability (ICC = 0.11-0.64). In conclusion, isokinetic strength of hip abductor and adductor muscles and the conventional and functional strength ratios can be reliably assessed in young soccer players, especially at low angular velocities. The assessment, however, of bilateral strength ratios for hip abductor/adductor muscles should be interpreted with more caution.     

Upper extremity kinematic and kinetic adaptations during a fatiguing repetitive task

Repetitive low-force contractions are common in the workplace and yet can lead to muscle fatigue and work-related musculoskeletal disorders. The current study aimed to investigate potential motion adaptations during a simulated repetitive light assembly work task designed to fatigue the shoulder region, focusing on changes over time and age-related group differences. Ten younger and ten older participants performed four 20-min task sessions separated by short breaks. Mean and variability of joint angles and scapular elevation, joint net moments for the shoulder, elbow, and wrist were calculated from upper extremity kinematics recorded by a motion tracking system. Results showed that joint angle and joint torque decreased across sessions and across multiple joints and segments. Increased kinematic variability over time was observed in the shoulder joint; however, decreased kinematic variability over time was seen in the more distal part of the upper limb. The changes of motion adaptations were sensitive to the task-break schedule. The results suggested that kinematic and kinetic adaptations occurred to reduce the biomechanical loading on the fatigued shoulder region. In addition, the kinematic and kinetic responses at the elbow and wrist joints also changed, possibly to compensate for the increased variability caused by the shoulder joint while still maintaining task requirements. These motion strategies in responses to muscle fatigue were similar between two age groups although the older group showed more effort in adaptation than the younger in terms of magnitude and affected body parts.     

Age-related fatigability in knee extensors and knee flexors during dynamic fatiguing contractions

This study investigated the effects of dynamic knee extension and flexion fatiguing task on torque and neuromuscular responses in young and older individuals. Eighteen young (8 males; 25.1 ± 3.2 years) and 17 older (8 males; 69.7 ± 3.7 years) volunteered. Following a maximal voluntary isometric contraction test, participants performed a fatiguing task involving 22 maximal isokinetic (concentric) knee extension and flexion contractions at 60°/s, while surface EMG was recorded simultaneously from the knee extensors (KE) and flexors (KF). Fatigue-induced relative torque reductions were similar between age groups for KE (peak torque decrease: 25.15% vs 26.81%); however, KF torque was less affected in older individuals (young vs older peak torque decrease: 27.6% vs 11.5%; p < 0.001) and this was associated with greater increase in hamstring EMG amplitude (p < 0.001) and hamstrings/quadriceps peak torque ratio (p < 0.01). Furthermore, KE was more fatigable than KF only among older individuals (peak torque decrease: 26.8% vs 11.5%; p < 0.001). These findings showed that the age-related fatigue induced by a dynamic task was greater for the KE, with greater age-related decline in KE compared to KF.     

Healthy older adults have insufficient hip range of motion and plantar flexor strength to walk like healthy young adults

Limited plantar flexor strength and hip extension range of motion (ROM) in older adults are believed to underlie common age-related differences in gait. However, no studies of age-related differences in gait have quantified the percentage of strength and ROM used during gait. We examined peak hip angles, hip torques and plantar flexor torques, and corresponding estimates of functional capacity utilized (FCU), which we define as the percentage of available strength or joint ROM used, in 10 young and 10 older healthy adults walking under self-selected and controlled (slow and fast) conditions. Older adults walked with about 30% smaller hip extension angle, 28% larger hip flexion angle, 34% more hip extensor torque in the slow condition, and 12% less plantar flexor torque in the fast condition than young adults. Older adults had higher FCU than young adults for hip flexion angle (47% vs. 34%) and hip extensor torque (48% vs. 27%). FCUs for plantar flexor torque (both age groups) and hip extension angle (older adults in all conditions; young adults in self-selected gait) were not significantly <100%, and were higher than for other measures examined. Older adults lacked sufficient hip extension ROM to walk with a hip extension angle as large as that of young adults. Similarly, in the fast gait condition older adults lacked the strength to match the plantar flexor torque produced by young adults. This supports the hypothesis that hip extension ROM and plantar flexor strength are limiting factors in gait and contribute to age-related differences in gait.     

Torque and force production during shoulder external rotation: differences between transverse and sagittal planes

In joints with 3 degrees of freedom, such as the shoulder joint, the association of different movements results in changes in the behavior of the moment arm of the muscles. The capacity of torque production for the same movement can be changed when movements take place in a different plane. The objective of this study is to quantify differences between torque production and resultant force estimated during the shoulder external rotation in two movement planes: the transverse and sagittal planes (with 90 degrees of shoulder abduction). Eight individuals were evaluated using an isokinetic dynamometer and an eletrogoniometer for movements in the transverse plane and six individuals for movements in the sagittal plane. The results showed that the execution of the external rotation in the sagittal plane allowed greater torque magnitudes and resultant force compared with those in the transverse plane, probably owing to a prestretching of infraspinatus and teres minor.     

The measurement and lateral comparison of the peak torque caused by the fast abduction exercise of stretched upper extremities in normal and trained adults

The maximal torque effect of the middle portion of action of the deltoid muscle while raising an outstretched upper limb was measured from left and right sides of normal untrained young adults and of the same age elite athletes. Seventeen strongly right-handed untrained males and females and 10 elite tennis players were tested. All participants were required to raise (abduct) one arm (right and then left, or vice versa) as fast as possible with maximal amplitude while standing on an electronic platform scale which measured to 0.001 kg. An assumed force at the centre of mass of the entire upper limb was considered. The force consisted of two components, namely static weight force of the upper limb and a dynamic force component created by upward acceleration of the limb. Using regression equations and scaling methods the static weight of the upper limb was derived and combined with the dynamic component to produce the total force, applied to the centre of mass of the limb. The total force multiplied by the distance from the centre of mass to point of rotation of the limb equated to the torque produced by deltoid muscle. Using video system analyses the angle of abduction was measured for each individual exercise. The additional anthropometrical tests identified proportionality and body mass indices for each participant.

There was no significant difference in dynamic force and torque between left and right limb from the three groups. Sportsmen demonstrated greater lateral abduction when performing the exercise from the dominant side of the body. Sportsmen also demonstrated greater range of abduction, bigger dynamic force and torque on both sides in comparison to untrained adults. Remarkably, the absolute and relative length of arms of athletes were shorter in comparison to untrained males, but the radius of gyration from the stretched upper limb (from its centre of gravity to the shoulder joint) were greater. This phenomenon may be due to distal shifting of the gravity center of the entire upper limb in elite athletes, perhaps, because greater investment of the distal portion of the limb with skeletal muscle tissue.     

Effects of joint angle and age on ankle dorsi- and plantar-flexor strength.

This study aimed at examining the effects of joint angle and age on the maximal voluntary contraction (MVC) torque, for the agonist and antagonist muscle groups around the ankle, i.e., the dorsi- and plantar-flexors. To this aim, neural and muscular factors were investigated in two groups of healthy men: 11 young (mean age, 24 years) and 18 older (mean age, 78 years). Plantar-flexion (PF) and dorsiflexion (DF) isometric MVC torques were measured in three different ankle joint angles and surface electromyographic activities of the triceps surae and of the tibialis anterior muscles were recorded. The main findings were that the DF-to-PF MVC torque ratio varied with joint angle and age, indicating that aging affected at different rates the two muscle groups: this ratio was always higher in older adults because of the PF strength decline with aging. Furthermore, the DF MVC torque-angle relationship appeared to be especially explained by neural factors, whereas the relationship in PF seemed to be mainly due to muscular parameters. These relationships would not be a discriminating factor between the two age groups. As a consequence, measurements at one ankle joint angle, whatever the angle, are thus enough to examine the differences within age groups and to perform a rapid assessment of the imbalance at the ankle joint.     

Estimations of relative effort during sit-to-stand increase when accounting for variations in maximum voluntary torque with joint angle and angular velocity

The main purpose of this study was to compare three methods of determining relative effort during sit-to-stand (STS). Fourteen young (mean 19.6 ± SD 1.2 years old) and 17 older (61.7 ± 5.5 years old) adults completed six STS trials at three speeds: slow, normal, and fast. Sagittal plane joint torques at the hip, knee, and ankle were calculated through inverse dynamics. Isometric and isokinetic maximum voluntary contractions (MVC) for the hip, knee, and ankle were collected and used for model parameters to predict the participant-specific maximum voluntary joint torque. Three different measures of relative effort were determined by normalizing STS joint torques to three different estimates of maximum voluntary torque. Relative effort at the hip, knee, and ankle were higher when accounting for variations in maximum voluntary torque with joint angle and angular velocity (hip = 26.3 ± 13.5%, knee = 78.4 ± 32.2%, ankle = 27.9 ± 14.1%) compared to methods which do not account for these variations (hip = 23.5 ± 11.7%, knee = 51.7 ± 15.0%, ankle = 20.7 ± 10.4%). At higher velocities, the difference in calculating relative effort with respect to isometric MVC or incorporating joint angle and angular velocity became more evident. Estimates of relative effort that account for the variations in maximum voluntary torque with joint angle and angular velocity may provide higher levels of accuracy compared to methods based on measurements of maximal isometric torques.     

Torque-velocity relationships for the knee extensors in women in their 3rd and 7th decades

Maximal isokinetic knee extensor strength was measured as torque in 17 young (mean age +/- SD, 21 +/- 3 years) and 16 elderly (68 +/- 5 years) women at 30 degrees (0.52 rad) before full extension, at angular velocities from 0 to 5.24 rad s-1, in 7 increments of 0.87 rad s-1. The elderly women were significantly weaker than the young women at all angular velocities. The rate of loss of absolute torque with increasing velocity was similar for both age groups, but when torque was standardised as a percentage of the individual's maximum, the elderly group showed a significantly greater rate of loss than the younger group. Quick-release from an isometric effort did not increase the recorded torques at 4.36 rad s-1 compared with the free-running method in either age group. The age differences are compatible with lower ratio of type II to type I fibre are in the older group.     

Isometric and isokinetic muscle strength, anthropometry and physical activity in 8 and 13 year old Swedish children

Isometric muscle strength of the hand-grip and of trunk flexion and extension, and isokinetic torque of elbow and knee flexion and knee extension were assessed in a random sample of 8 and 13 year old Swedish children. The results were compared with respect to sex and age in absolute terms and relative to weight, height2 and estimates of lean body mass and cross-sectional muscle area. Daily physical activity was also estimated. The muscle strength variables were in general found to be very similar in the 8 year old boys and girls. In the 13 year old group the boys were generally stronger than the girls, in both absolute and relative terms, except for similar torque values during knee extension. The absolute and relative muscle strength and torque values were higher in the older than in the younger children, with the exception of trunk strength per unit of body weight and of lean body mass, which were similar in boys of both ages and significantly lower in the older than in the younger girls. No significant correlation was found between the estimates of physical activity and isometric and isokinetic muscle strength and torque.     

Effects of aging on hip abductor-adductor neuromuscular and mechanical performance during the weight transfer phase of lateral protective stepping

Aging brings about challenges in the ability to recover balance through protective stepping, especially in the lateral direction. Previous work has suggested that lateral protective stepping during weight transfer may be affected by impaired muscle composition and performance of the hip abductors (AB) in older adults. Hence, this study investigated the influence of hip abductor-adductor (AB-AD) neuromuscular performance on the weight transfer phase of lateral protective stepping in younger and older adults. Healthy younger (n = 15) and older adults (n = 15) performed hip AB-AD isometric maximal voluntary contractions (IMVC). Lateral balance perturbations were applied via motorized waist-pulls. Participants were instructed to recover their balance using a single lateral step. Kinetic, kinematic and electromyographic (EMG) data were analyzed during the weight transfer phase. In the hip IMVC task, older adults showed reduced peak AB-AD torque, AB rate of torque development and AB-AD rate of EMG neuromuscular activation (RActv). During the lateral balance perturbations, older individuals had a lower incidence of lateral steps, reduced hip AB-AD RActv and delayed weight transfer. However, several outcomes were larger in the older group, such as, center of mass momentum at step onset, step-side peak rate of vertical force development, hip AB net joint torque, and power. Although older adults had greater hip muscular output during the weight transfer phase, their lateral balance recovery was still impaired. The reduced maximal hip AB-AD capacity, especially RActv, may have been a greater contributor to this impairment, as it affects the ability to generate rapid force, crucial for balance recovery.     

Effect of rest interval on strength recovery in young and old women

This study compares the effects of rest intervals on isokinetic muscle torque recovery between sets of a knee extensor and flexor exercise protocol in physically active younger and older women. Twenty young (22.4 +/- 1.7 years) and 16 older (70.7 +/- 4.3 years) women performed three sets of eight maximum repetitions of knee extension/flexion at 60 degrees x s(-1). The rest interval between sets was 15, 30, and 60 seconds and was randomly assigned across three testing days. No significant interaction of rest by set by age group was observed. There was a significant decline in mean knee extensor torque when 15- and 30-second rest intervals were used between sets, but not when a 60-second rest interval was applied for both the young and the old women. No significant decline for mean knee flexor torque was observed in the older women when a 30-second rest interval was used, whereas a longer 60-second rest interval was required in younger women. Active younger and older women require similar rest intervals between sets of a knee extensor exercise (60 seconds) for complete recovery. However, older women recovered faster (30 seconds) than younger women (60 seconds) between sets of a knee flexor exercise. The exercise-to-rest ratio for knee extensors was similar for young and old women (1:2). Old women required only a 1:1 exercise-to-rest ratio for knee flexor recovery, whereas younger women required a longer 1:2 exercise-to-rest ratio. The results of the present study are specific to isokinetic testing and training and are more applicable in rehabilitation and research settings. Practitioners should consider age and gender when prescribing rest intervals between sets.     

Cardiorespiratory and subjective responses to prolonged arm and leg exercise in healthy young and older men

Ten young (aged 23–30 years) and nine older (aged 54–59 years) healthy men with a similar size of limb muscle mass performed arm crank and leg cycle exercise for 30 min at relative exercise intensities of 50% and 75% of maximal oxygen uptake for the corresponding muscle group. In the tests, heart rate, blood pressure, gas exchange variables, rating of perceived exertion and blood lactate concentration were measured. The limb muscle mass was determined by anthropometric measurements. At the 75% target exercise level, four of the older men and two of the young men could not complete the arm-cranking test, and one of the older men and two of the young men could not complete the leg-cycle test. During arm-cranking the absolute exercise intensity was similar for the young and older men because of similar maximal values during arm-cranking. But during leg-cycling the absolute excercise intensity was higher for the young men than for the older men due to the difference in corresponding maximal values. During arm-cranking there were no significant differences in the physiological responses between the age groups except that a higher ventilatory response was noted among the older compared to the young men. During leg-cycling the heart rate values were higher among the young compared to the older men. But, when the heart rate values were expressed as a percentage of maximal heart rate in the corresponding maximal tests, no significant differences between the age groups were found. The results indicated that 30-min of arm or leg exercise at the same relative submaximal excercise intensity produces a similar degree of physiological strain in healthy older compared to young men. During arm-cranking, the young and the older men exercised at the same external intensity, indicating a similar ability to perform prolonged excercise using smaller muscle groups expressed both in absolute and relative terms. Accepted: 7 October 1996     

Theoretical contribution of the upper extremities to reducing trunk extension following a laboratory-induced slip

Slips are frequently the cause of fall-related injuries. Identifying modifiable biomechanical requirements for successful recovery is a key prerequisite to developing task-specific fall preventive training programs. The purpose of this study was to quantify the biomechanical role of the upper extremities during the initial phase of a slip resulting in trunk motion primarily in the sagittal plane. Two groups of adults were examined: adults over age 65 who fell and adults aged 18–40 who avoided falling after slipping. We hypothesized that rapid shoulder flexion could significantly reduce trunk extension velocity, that adults who slipped would implement this as a fall avoidance strategy, and that younger adults who avoided falling would use this strategy more effectively than older adults who fell. The kinematics of the 12 younger adults and eight older adults were analyzed using a three-segment conservation of momentum model developed to represent the trunk, head, and upper extremities. The model was used to estimate the possible contribution of the upper extremities to reducing trunk extension velocity. The model showed that upper extremity motion can significantly reduce trunk extension velocity. Although the upper extremities significantly reduced the trunk extension velocity of both young and older adults (p<0.027), the reduction found for the young adults, 13.6±11.4%, was significantly larger than that of the older adults (5.8±3.4%, p=0.045). Given the potential for trunk extension velocity to be reduced by rapid shoulder flexion, fall prevention interventions focused on slip-related falls may benefit from including upper extremity motion as an outcome whether through conventional or innovative strategies.