Peak Elbow Research Articles

Kinematics and Kinetics of the Racket-Arm during the Soft-Tennis Smash under Match Conditions

The purposes of this study were to (a) describe the racket-arm kinematics and kinetics of the soft-tennis smash during match rallies, and (b) assess the characteristics of this smash vs. the laboratory-simulated smash of our previous study. In the current study we recorded soft-tennis smash motions during match play of the 3rd East Asian Games. Racket-arm anatomical joint angular velocity and anatomical joint torque were calculated from 3-D coordinate data of 13 collected motions obtained using the direct linear transformation procedure. The results showed that most of the maximum values of the anatomical joint torques were qualitatively smaller than those of the tennis serve. Peak elbow extension, shoulder internal rotation, and elbow varus torques in match play were significantly greater than values reported for laboratory-simulated conditions. The greater forward swing torques did not result in significantly different racket head velocity, possibly because there was a significantly shorter forward swing phase in match conditions. In particular, a clear peak of the elbow extension torque during the forward swing phase was the most characteristic pattern in the smashes under match conditions, for it was 160% greater than laboratory-simulated conditions. These results supported our hypothesis that racket-arm kinematic and kinetic characteristics of the smash under match conditions differ from those under laboratory-simulated conditions. Possible explanations include the time-pressure conditions of the competitive situation in a match, and the Hawthorne effect (Hudson et al., 1986), both of which alter performance between match conditions and laboratory-simulated conditions.

Strength deficits in primary focal hand dystonia

Cortical activation is reduced when patients with focal dystonia perform movements that do not induce dystonic posturing. This finding suggests that the cortical drive to muscles may in some circumstances actually be reduced not increased, as suggested by basal ganglia models of dystonia as a hyperkinetic disorder. The purpose of this study was to examine flexor and extensor strength at the wrist (a clinically affected joint) and elbow (a nonclinically affected joint) in 18 patients with primary focal hand dystonia compared to matched control subjects. We measured peak torque from maximum voluntary contractions, and agonist and antagonist muscle activation by means of surface electromyograms. Patients were significantly weaker than controls at both the elbow and wrist joints and in both flexors and extensors compared to controls. Peak elbow flexion torque was, on average, 14.4% lower in the dystonic compared to the control group, elbow extensor peak torque was 28.6% lower, wrist flexor peak torque was 17.4% lower, and wrist extensor peak torque was 20.7% lower. Strength did not differ as a function of clinical severity. Reductions in peak torque were accompanied by reduced agonist activation, although this finding only reached statistical significance at the elbow. The amount of co-contraction of antagonistic muscles was not significantly different between the two groups. These results are discussed in the context of dystonia as a disorder resulting from dysfunction of basal ganglia output.

Accuracy of Visual Estimates of Joint Angle and Angular Velocity Using Criterion Movements

A descriptive study to document undergraduate physical education majors' (22.8 +/- 2.4 yr. old) estimates of sagittal plane elbow angle and angular velocity of elbow flexion visually was performed. 42 subjects rated videotape replays of 30 movements organized into three speeds of movement and two criterion elbow angles. Video images of the movements were analyzed with Peak Motus to measure actual values of elbow angles and peak angular velocity. Of the subjects 85.7% had speed ratings significantly correlated with true peak elbow angular velocity in all three angular velocity conditions. Few (16.7%) subjects' ratings of elbow angle correlated significantly with actual angles. Analysis of the subjects with good ratings showed the accuracy of visual ratings was significantly related to speed, with decreasing accuracy for slower speeds of movement. The use of criterion movements did not improve the small percentage of novice observers who could accurately estimate body angles during movement.

Excess Adiposity Limits The Muscle Strength Response To Resistance Training

Evidence is limited but suggests that overweight and obesity may attenuate the muscle strength response to resistance training (RT). PURPOSE To investigate the influence of overweight and obesity on the muscle strength and size adaptations to a 12 wk unilateral, upper arm RT program in a large sample of apparently healthy, young adults. METHODS Subjects were 449 normal weight (NW) (mean ± SEM) (22.0 ± 0.1 kg/m2, 23.3 ± 0.2 yr) and 238 overweight to obese (OW) (29.2 ± 0.3 kg/m2, 25.6 ± 0.4 yr) men (n=285) and women (n=402) who had not performed RT for 1 yr prior to study participation. Subjects underwent 12 wks (2 d/wk) of supervised RT on the non-dominant arm. Peak elbow flexor muscle strength (kg) was evaluated by isometric testing and 1 repetition maximum (1RM). Biceps muscle cross sectional area (cm2) was measured by magnetic resonance imaging. Muscle strength data were analyzed with no correction (absolute), corrected for baseline strength values (relative), and scaled for body weight by the allometric method (allometric). Biceps cross sectional area was analyzed with no correction (absolute) and corrected for initial values (relative). Multivariate ANOVA was used to detect if muscle strength and size differed between NW and OW pre-RT, post-RT, and pre- to post-RT. RESULTS OW had greater pre-RT absolute elbow flexor peak isometric (50.4 ± 1.0 vs 42.2 ± 0.7 kg) and 1RM (10.1 ± 0.2 vs 8.3 ± 0.1 kg) strength and biceps size (19.5 ± 0.3 vs 16.4 ± 0.2 cm2) than NW (p <0.001). Similarly, OW had greater post-RT absolute elbow flexor peak isometric (58.1 ± 1.1 vs 50.6 ± 0.8 kg) and 1RM (14.2 ± 0.2 vs 12.4 ± 0.1 kg) strength and biceps size (23.1 ± 0.4 vs 19.6 ± 0.3 cm2) than NW (p <0.001). Absolute peak elbow flexor strength gains were similar between OW and NW pre- to post-RT. In contrast, NW had greater relative peak elbow flexor isometric (21.2 ± 1.0 vs 17.4 ± 1.4%) and 1RM (54.3 ± 1.5 vs 49.0 ± 2.0%) strength increases than OW pre- to post-RT (p <0.05). Further, NW had greater allometric peak elbow flexor isometric (0.48 ± 0.02 kg·kg−0.67 vs 0.40 ± 0.03 kg·kg−0.67) and 1 RM (0.25 ± 0.00 vs 0.22 ± 0.01 kg·kg−0.67) strength increases than OW pre- to post-RT (p <0.05). Absolute biceps size gains were greater in OW than NW (p <0.001); however, relative biceps size increases were similar between OW and NW (18.4 ± 0.7 vs 19.4 ± 0.5%) pre- to post-RT. CONCLUSION Despite similar relative increases in biceps size, NW had greater relative and allometric gains in peak elbow flexor strength than NW. Excess overall adiposity may limit the muscle strength response to RT in young adults. Supported by NIH-NINDS R01 NS40606-02

Ace I/d Polymorphism Alters The Muscle Strength Response To Resistance Training

PURPOSE The Angiotensin Converting Enzyme Insertion allele (ACE I) is favorably associated with endurance performance, whereas the ACE Deletion allele (ACE D) with muscle strength and power-oriented performance. The purpose of this study was to examine if the ACE I/D polymorphism was related to the muscle strength and size responses to a unilateral, upper arm resistance training (RT) program among apparently healthy, young adults. We hypothesized the ACE D allele would be associated with greater increases in muscle strength and size than the ACE I allele. METHODS Subjects were 620 (mean ± SEM, 24.5±1.7 yr) mostly white (80%), mean (42%) and women (58%) who had not performed RT in the previous yr. Subjects completed 12 wk (2 d/wk) of supervised upper-arm RT. Peak elbow flexor muscle strength (kg) was assessed by isometric testing and 1 repetition maximum (1RM). Biceps muscle cross sectional area (cm2) was measured by magnetic resonance imaging. Multivariate ANOVA tested if muscle strength and size differed between ACE I/D pre-RT, post-RT, and pre- to post-RT. Because ACE II (n=146) and ID (n=288) did not differ in their RT response, these genotypes were combined and data are reported for ACE II/ID (n=434) versus DD (n=186). RESULTS Pre-RT absolute elbow flexor peak isometric (45.0±0.7 vs 45.4±1.1 kg) and 1RM (9.1±0.1 vs 9.2±0.2 kg) strength and biceps size (17.9±0.2 vs 17.2±0.4 cm2) did not differ between ACE II/ID and DD, respectively. Similarly, post-RT absolute elbow flexor peak isometric (53.6±0.8 vs 52.2±1.3 kg) and 1RM (13.1±0.1 vs 13.2±0.2 kg) strength and biceps size (21.2±0.3 vs 20.6±0.4 cm2) were not different between ACE II/ID and DD (p > 0.05). Absolute (8.6±0.4 vs 6.8±0.6 kg), relative (% of initial values) (22.2±1.0 vs 16.8±1.6 %) and allometric (0.5±0.0 vs 0.4±0.0 kg*kg−0.67) peak elbow flexor isometric strength increases pre- to post-RT were greater for ACE II/ID than DD, respectively (p < 0.01). In contrast, absolute (4.0±0.1 vs 4.0±0.1 kg), relative (51.0±1.5 vs 51.2±2.3 %) and allometric (0.2±0.0 vs 0.2±0.0 kg*kg−0.67) peak elbow flexor strength gains as measured by 1RM; and absolute (3.3±0.1 vs 3.4±0.1 cm2) and relative (18.6±0.5 vs 19.9±0.8 %) muscle size gains were not different between ACE II/ID and DD pre- to post-RT (p > 0.05). CONCLUSION Contrary to our hypothesis, ACE DD gained less peak elbow flexor isometric strength than ACE II/ID genotypes pre- to post-RT, despite similar gains in 1RM and muscle size. Reasons for these differences between the muscle strength response to RT and ACE I/D genotypes are not clear and merit further investigation. Supported by NIH-NINDS R01 NS40606-02

Ace I/d Polymorphism Alters The Muscle Strength Response To Resistance Training

PURPOSE The Angiotensin Converting Enzyme Insertion allele (ACE I) is favorably associated with endurance performance, whereas the ACE Deletion allele (ACE D) with muscle strength and power-oriented performance. The purpose of this study was to examine if the ACE I/D polymorphism was related to the muscle strength and size responses to a unilateral, upper arm resistance training (RT) program among apparently healthy, young adults. We hypothesized the ACE D allele would be associated with greater increases in muscle strength and size than the ACE I allele. METHODS Subjects were 620 (mean ± SEM, 24.5±1.7 yr) mostly white (80%), mean (42%) and women (58%) who had not performed RT in the previous yr. Subjects completed 12 wk (2 d/wk) of supervised upper-arm RT. Peak elbow flexor muscle strength (kg) was assessed by isometric testing and 1 repetition maximum (1RM). Biceps muscle cross sectional area (cm2) was measured by magnetic resonance imaging. Multivariate ANOVA tested if muscle strength and size differed between ACE I/D pre-RT, post-RT, and pre- to post-RT. Because ACE II (n=146) and ID (n=288) did not differ in their RT response, these genotypes were combined and data are reported for ACE II/ID (n=434) versus DD (n=186). RESULTS Pre-RT absolute elbow flexor peak isometric (45.0±0.7 vs 45.4±1.1 kg) and 1RM (9.1±0.1 vs 9.2±0.2 kg) strength and biceps size (17.9±0.2 vs 17.2±0.4 cm2) did not differ between ACE II/ID and DD, respectively. Similarly, post-RT absolute elbow flexor peak isometric (53.6±0.8 vs 52.2±1.3 kg) and 1RM (13.1±0.1 vs 13.2±0.2 kg) strength and biceps size (21.2±0.3 vs 20.6±0.4 cm2) were not different between ACE II/ID and DD (p > 0.05). Absolute (8.6±0.4 vs 6.8±0.6 kg), relative (% of initial values) (22.2±1.0 vs 16.8±1.6 %) and allometric (0.5±0.0 vs 0.4±0.0 kg*kg−0.67) peak elbow flexor isometric strength increases pre- to post-RT were greater for ACE II/ID than DD, respectively (p < 0.01). In contrast, absolute (4.0±0.1 vs 4.0±0.1 kg), relative (51.0±1.5 vs 51.2±2.3 %) and allometric (0.2±0.0 vs 0.2±0.0 kg*kg−0.67) peak elbow flexor strength gains as measured by 1RM; and absolute (3.3±0.1 vs 3.4±0.1 cm2) and relative (18.6±0.5 vs 19.9±0.8 %) muscle size gains were not different between ACE II/ID and DD pre- to post-RT (p > 0.05). CONCLUSION Contrary to our hypothesis, ACE DD gained less peak elbow flexor isometric strength than ACE II/ID genotypes pre- to post-RT, despite similar gains in 1RM and muscle size. Reasons for these differences between the muscle strength response to RT and ACE I/D genotypes are not clear and merit further investigation. Supported by NIH-NINDS R01 NS40606-02

KINEMATICS OF BIOPHYSICALLY ASYMMETRIC LIMBS WITHIN RATE OF VELOCITY DEVELOPMENT

The purpose of this study was to investigate the movement speed characteristics of 2 intrinsically different limbs. Twenty subjects volunteered to participate (10 men and 10 women). Each subject performed 5 repetitions of concentric knee and elbow extension and flexion movements at 60 through 500 d·s-1 on an isokinetic dynamometer. Kinematic data were collected at 1,000 Hz and separated into rate of velocity development (RVD) and peak torque. Results demonstrated a significant (p < 0.05) main effect for sex for RVD and peak torque. Significant (p < 0.05) differences were also demonstrated between knee and elbow RVD and between knee and elbow peak torque at every speed tested. Neither knee and elbow RVD nor peak torque demonstrated any significant Pearson correlations at any speed tested (r = 20.17–0.41). These results collectively point to the specificity of limb speed and torque as a result of biophysical differences such as length and mass. Therefore, strength and speed may be modulated by neuromotor patterns that differ based on individual limbs.

Differences in multi-joint kinematic patterns of repetitive hammering in healthy, fatigued and shoulder-injured individuals

Work-related musculo-skeletal disorders have been previously related to movement repetition, inadequate postures, non-ergonomic environments, muscular imbalance and fatigue. However, no direct link between fatigue and injury has been experimentally shown. To address this problem, we compared the effects of fatigue and injury on the kinematics of repetitive hammering. Healthy subjects (n=30) hammered repetitively both before and after fatigue. Fatigue was induced by a combination of static and dynamic procedures. Shoulder-injured subjects (n=15) hammered for 30s without fatigue. Kinematics of motion was recorded. The movement time and shoulder range of motion during hammering were not affected by either fatigue or shoulder injury. When fatigued, the healthy subjects displayed decreased range of joint motion, peak velocity and peak acceleration of elbow motion during hammering as well as reduced grip strength. Shoulder-injured individuals had a smaller hammer trajectory amplitude than healthy controls with or without fatigue. They also had lower wrist range of motion, elbow peak velocity, and peak wrist and elbow acceleration compared to healthy subjects hammering without fatigue but only lower wrist peak acceleration compared to healthy subjects hammering with fatigue. Results showed that fatigue affects elbow motion while shoulder injury affects both wrist and elbow motions during hammering. However, shoulder kinematics were not changed by either fatigue or shoulder injury. These changes at the wrist and elbow may reflect strategies used by individuals with shoulder injury to maintain constant movement duration and shoulder kinematics during movement.

Kinematics of Biophysically Asymmetric Limbs Within Rate of Velocity Development

The purpose of this study was to investigate the movement speed characteristics of 2 intrinsically different limbs. Twenty subjects volunteered to participate (10 men and 10 women). Each subject performed 5 repetitions of concentric knee and elbow extension and flexion movements at 60 through 500 d.s(-1) on an isokinetic dynamometer. Kinematic data were collected at 1,000 Hz and separated into rate of velocity development (RVD) and peak torque. Results demonstrated a significant (p < 0.05) main effect for sex for RVD and peak torque. Significant (p < 0.05) differences were also demonstrated between knee and elbow RVD and between knee and elbow peak torque at every speed tested. Neither knee and elbow RVD nor peak torque demonstrated any significant Pearson correlations at any speed tested (r = -0.17-0.41). These results collectively point to the specificity of limb speed and torque as a result of biophysical differences such as length and mass. Therefore, strength and speed may be modulated by neuromotor patterns that differ based on individual limbs.

Valgus torque in youth baseball pitchers: a biomechanical study

The purpose of this study was to determine the biomechanical and anthropometric factors contributing to elbow valgus torque during pitching. Video data of 14 youth pitchers throwing fastballs were used to calculate shoulder and elbow kinematics and kinetics. Peak elbow valgus torque averaged 18 Nm and occurred just before maximal shoulder external rotation. The magnitude of valgus torque was most closely correlated with the thrower's weight. When subject weight and height were controlled for, maximum shoulder abduction torque and maximum shoulder internal rotation torque were most strongly associated with elbow valgus torque, accounting for 85% of its variance ( P < .001). When only kinematic variables were considered, maximum shoulder external rotation accounted for 33% of the variance in valgus torque. Given that the biomechanical variables correlated with peak valgus torque are not easily modifiable, limiting the number of innings pitched is likely the best way to reduce elbow injury in youth pitchers.

Target-dependent differences between free and constrained arm movements in chronic hemiparesis.

This study compares the kinematic and kinetic characteristics of constrained and free upper limb movements in eight subjects with chronic hemiparesis. Movements of the dominant and nondominant limbs were also examined in five control subjects. Rapid movements were performed in the horizontal plane from a central starting point to five targets located to require various combinations of flexion/extension rotations at the elbow and shoulder. Support of the upper limb against gravity loading was provided either by a low-friction air-bearing apparatus (constrained condition) or by voluntary generation of abduction and external rotation torques at the shoulder (free condition). Data analysis focused on the peak joint torques generated during the acceleratory phase of movement, and on the net change in joint angles at the elbow and shoulder. We found that movement parameters were broadly invariant with support condition for either limb of control subjects, as well as for the nonparetic limb of hemiparetic subjects. In contrast, support condition had a target-dependent effect on movements of the paretic limb. Relative to the constrained condition, peak torques for free arm movements were significantly reduced for distal targets requiring elbow extension and/or shoulder flexion torques. However, peak elbow flexion and shoulder extension joint torques for proximal targets were relatively unaffected by support condition. Of perhaps more functional importance, free movements were characterized by a target-dependent restriction in the hand's work area that reflected a reduced range of active elbow extension, relative to constrained movements. The target-dependent effects of support condition on movements of the paretic limb are consistent with the existence of abnormal constraints on muscle activation patterns in subjects with chronic hemiparesis, namely an abnormal linkage between activation of the elbow flexors and shoulder extensors, abductors, and external rotators.

Medial Collateral Ligament Reconstruction

Medial Collateral Ligament Reconstruction

Effect of muscle length on strength and dexterity after stroke.

The effect of muscle length on strength and dexterity after stroke was investigated. The aim was to determine if poor function at a particular muscle length could be attributed solely to differential weakness at this joint angle or whether an additional problem of differential dexterity exists. This descriptive research study measured elbow flexor and extensor strength as well as dexterity at three elbow joint angles: 30 degrees , 60 degrees and 90 degrees flexion. Dexterity was measured independently of strength. Fifteen (seven female, eight male) chronic stroke patients (mean age 67 years) who could actively flex and extend their affected elbow participated. Ten neurologically normal control subjects (mean age 67 years) acted as controls. Strength was measured as peak elbow flexor and extensor torque at three angles; and dexterity was measured as coherence for slow and fast tracking also at three angles. Dexterity was not affected by muscle length but strength was and this finding was the same for both stroke and controls. While the magnitude of the torque-angle curves was not significantly different between stroke and controls, the shape of torque-angle curves was altered after stroke so that both the elbow flexors (p < 0.05) and extensors (p < 0.05) tested weaker in the testing position where they were shortest. Since there was no differential loss of dexterity, it appears that differential loss of strength, especially in the shortened range, may explain the clinical observation of poorer function at one muscle length than another after stroke. Specific training to strengthen the muscles in these ranges is therefore of clinical importance for rehabilitation.

Moment distribution among human elbow extensor muscles during isometric and submaximal extension

To understand better how the central nervous system (CNS) distributes a joint moment among muscles, moment distribution among the three heads of the triceps and the anconeus muscles during isometric elbow extension was quantified in vivo and noninvasively. Electrical stimulation was used to activate an individual muscle selectively at various contraction levels, and the relationship between the peak M-wave amplitude and peak elbow extension moment was established across various contraction levels for each muscle. The relationship was then used to calibrate the corresponding EMG signal and determine moment distribution among the muscles during voluntary isometric elbow extension. Results showed that moment distribution among muscles was not proportional to the muscles’ physiological cross-sectional areas (PCSA) and the CNS favored uniarticular muscles for the isometric task performed: the uniarticular lateral and medial heads of the triceps were dominant (contributing ∼70–90% of the total elbow extension moment) and the anconeus contributed significantly, especially at the lower levels of elbow extension moment (up to ∼15% of the extension moment). In contrast, the two-joint long head of the triceps contributed significantly less than the uniarticular heads of the triceps. While the absolute contributions of all the muscles increased with the total elbow extension moment, the relative contributions of the muscles may increase or decrease with the elbow extension moment. Cross-validation using fresh data (not used in determining the moment distribution) showed close match between the measured and predicted elbow extension moment except for trials in which fatigue became significant.

Slowness to develop force contributes to weakness after stroke

Objective: To examine weakness after stroke, in terms of both level and rate of torque generation. Design: Descriptive. T tests for dependent and independent samples and Pearson's product moment correlation coefficients were performed. Setting: A rehabilitation unit. Participants: Ten stroke subjects, aged 56 to 81 years, undergoing rehabilitation. Ten neurologically normal subjects aged 55 to 78 years were the controls. Outcome Measures: Peak isometric elbow flexor and extensor torque and time to 90% peak elbow flexor and extensor torque at 6 weeks and at 25 weeks after stroke. Results: At 6 weeks after stroke, subjects were only half as strong and took two to three times longer to produce torque compared to controls ( p ≤ .05). By 25 weeks after stroke, significant improvements in peak torque ( p ≤ .02) and time to 90% peak flexor torque ( p ≤ .05) were seen so that values were within normal limits. Conclusion: Decreased rate of torque development compounds the problem of reduced peak torque, which may have significant implications for stroke patients, especially in situations where muscles are very weak or where force needs to be generated quickly.

FOREARM ANTHROPOMETRY AND ELBOW VIBRATIONS OF TENNIS PLAYERS WITH AND WITHOUT ELBOW PAIN 704

One of the many factors attributed to the development of “tennis elbow” or lateral epicondylitis is the transfer of racket vibrations onto the forearm. Heavier subjects tend to have reduced arm vibrations, but no attempt has been made to study the forearm physical characteristics and the vibrations transferred to the elbow of players with (WP) and without elbow pain (WOP). Twenty-three female players of the same skill level [14 WOP and 9 WP] were tested using an ENTRAN uniaxial accelerometer encased in balsa wood and fastened using an elastic band over the lateral epicondyle, aligned with the humerus. Dunlop Super Revelation rackets (stiff) with different grip sizes and equal string tension (275 N) were used in the study. A ball machine was used to ensure proper ball velocity (11.1 ± 1.4 m/s) and alignment. Each subject performed 5 off-center (10 cm) and 5 on-center static backhand trials. The anthropometric variables taken were (age, height, grip size, hand size, forearm circumference and length, wrist circumference and range of motion, and grip strength. Pearson Product moment correlation's and t-test's for independent means were used to analyze the data. Elbow peak accelerations immediately after impact were.48 ±.10 and.59 ± 1.5 g for the center and the off-center hits, respectively (p<.05). No significant correlation's were found between the off-center and center peak accelerations and the anthropometric variables. Although not significant, there were strong correlation's between body weight and center and off-center peak accelerations[r=-.63 & -.50 WP, r=-.48 & -.48 WOP]. Age was the only significant factor between the WP ([horizontal bar over]x = 45) and the WOP ([horizontal bar over]x = 39). These results suggest that forearm anthropometric differences are not a significant factor in the transmission of racket vibrations at the lateral epicondyle of people with elbow pain.

EMG changes in agonist muscles during practice of a multijoint throwing skill

The purpose of this investigation was to determine, for a planar multijoint throwing skill, if electromyographic (EMG) amplitudes of eccentric and concentric muscle activity for two agonist muscles (i.e. agonists for the concentric phase) changed over the course of practice. Eighteen men threw a weighted ball with their dominant arm at a target while the motion was restrained to a horizontal plane. EMG and kinematic data were collected for selected practice trials. EMG signals of the triceps brachii (lateral head) and posterior deltoid were full-wave rectified and integrated (IEMG) over two portions of the movement: the countermovement and the throw. Performance showed an expected improvement over trial blocks. IEMG activities of both muscles did not change across trial blocks for the countermovement (eccentric phase) or for the throw (concentric phase) even though several kinematic and kinetic descriptors changed significantly (e.g. during the throw, peak elbow angular velocity and mechanical work by the elbow extensor moment increased during practice). Results suggest that EMG amplitudes of assistive or auxiliary muscles may change rather than primary agonists or that limitations inherent in skill acquisition research and EMG signal processing may be the reasons why no changes were observed in EMG amplitudes.

Kinematic analysis of reaching in the cat

The present study examines the kinematic features of forelimb movements made by cats reaching for food in horizontal target wells located at different heights and distances. Wrist paths consisted of two relatively straight segments joined at a "via-point" in front of the aperture of the food well. In the initial lift phase, the paw was raised to the via-point in front of the target. In the second, or thrust phase, the paw was directed forward into the food well. During the lift, the paw was moved toward the target primarily by elbow flexion, accompanied by a sequence of biphasic shoulder and wrist movements. Thrust was accomplished primarily by shoulder flexion while the wrist and the paw were maintained at near-constant angles. The animals varied the height of the reach primarily by varying elbow flexion with proportional changes in elbow angular velocity and angular acceleration and with corresponding variations in wrist speed. Thus, cats reached for targets at different heights by scaling a common kinematic profile. Over a relatively large range of target heights, animals maintained movement duration constant, according to a simple "pulse-height" control strategy (isochronous scaling). For reaches to a given target height, animals compensated for variability in peak acceleration by variations in movement time. We examined the coordination between the shoulder and the wrist with the elbow. Early during the lift, peak shoulder extensor and peak elbow flexor accelerations were synchronized. Late during the lift phase, wrist extensor acceleration was found to occur during the period of elbow flexor deceleration. We hypothesize that these linkages could, in part, be due to passive mechanical interactions. To determine how the angular trajectories of the different joints were organized in relation to target location, we plotted joint kinematic changes directly on the wrist and MCP joint paths. These plots revealed that for all target heights and movement speeds, wrist extensor deceleration occurred at approximately the same spatial location with respect to the target. This analysis also demonstrated that the second phase of MCP flexion occurred when the paw was below the lower lip of the food well, while the subsequent extension occurred after the tip cleared this obstacle. During thrust, wrist and MCP angles were maintained, reflecting the need to align the paw within the food well. Our findings suggest that cats plan the reaching phase of prehension as a sequence of discrete movement segments, each serving a particular goal in the task, rather than as an single unit.

Central and peripheral fatigue of human diaphragm and limb muscles assessed by twitch interpolation.

1. This study used a sensitive modification of the twitch interpolation technique to compare the extent of voluntary neural drive to the diaphragm and the elbow flexors during fatigue. For the diaphragm both inspiratory and expulsive efforts were tested, and fatigue was induced by expulsive efforts which were either maximal voluntary contractions (MVCs, 10 s duration, 50% duty cycle) or submaximal contractions (50% MVC, 3 s duration, 60% duty cycle). 2. Over the series of thirty MVCs peak elbow torque declined to 57.9 +/- 3.0% (mean +/- S.E.M.) of the initial value while maximal inspiratory pressure declined to 78.7 +/- 7.3% (P < 0.05). For the diaphragm the relative decline in voluntary peak inspiratory (and expulsive) force was similar to the decline in twitch responses to single and twin (10 ms interval) stimuli. However, for the elbow flexors the decline in twitch force was disproportionately greater than the decline in maximal voluntary force. The decline in twitch force for the diaphragm could not be attributed to failure at the neuromuscular junction. 3. At the start of the exercise, twitch potentiation (following three brief MVCs) was significantly less for the diaphragm than for the elbow flexors (20% versus 61%, P < 0.01). 4. In the unfatigued state maximal voluntary efforts by subjects activated 98.4 +/- 0.4% of the stimulated elbow flexors compared with 95.0 +/- 1.5% of the diaphragm (P < 0.05). During the exercise period there was a progressive failure in the ability to activate the limb muscle ('central fatigue'; voluntary drive declined from 98.4 +/- 0.4 to 86.8 +/- 2.2%, P < 0.01) whereas the decline in voluntary activation during inspiratory contractions was not significant (from 95.0 +/- 15 to 91.5 +/- 2.5%). 5. Voluntary activation during attempted maximal efforts was less complete for both muscles when stimuli were delivered without warning. The index of voluntary activation for unwarned stimuli was lower for the diaphragm (performing expulsive efforts, 81.0 +/- 2.8%) than for the limb muscle (89.9 +/- 1.5%, P < 0.01). 6. During repeated submaximal expulsive efforts we confirmed that subjects develop a marked inability to contract the diaphragm voluntarily, but when the diaphragm performed inspiratory manoeuvres at the same level of contractile fatigue, the index of voluntary drive was greater than 94%. 7. In conclusion, when tested with inspiratory efforts the diaphragm developed less central fatigue than the limb muscle over the same exercise period.(ABSTRACT TRUNCATED AT 400 WORDS)

The Relationship Between Isokinetic Power and Selected Anaerobic Power Tests

. The purpose of this study was to determine the relationship between selected anaerobic power tests and isokineticpeak torque values and a criterion power measure established by the sum of several isokinetic power outputs. Forty college-age men participated in the study. The selected anaerobic power tests included the Margaria-Kalaman stair test, vertical jump, and leg and arm cranking power. Peak torque values were obtained from knee and elbow flexion and extension at 60 and 240 deg/sec. The results showed correlations (r) between the tests and the criterion ranged from r = 0.43 to r = 0.84 (p < 0.01). Multiple regression analysis was used to determine the percent of variance in the criterion that could be explained by the selected tests. Three significant (p < 0.01) equations were developed with multiple correlations (R) ranging from R = 0.84 to R = 0.92. Up to 85% of the variation in the criterion can be explained by the following test performances (in order of influence): the Margaria-Kalaman, summed peak elbow torques at 240 deg/sec, and leg cranking power.