Isokinetic Plantar Flexion Research Articles

Dynamometric Indicators of Fatigue From Repeated Maximal Concentric Isokinetic Plantar Flexion Contractions Are Independent of Knee Flexion Angles and Age but Differ for Males and Females

Sex and age are reported to influence the maximal dynamometric performance of major muscle groups, inclusive of ankle plantar flexors. Knee flexion (KF) also impacts plantar flexion function from where stems use of 0° and 45° angles of KF for clinical assessment of gastrocnemius and soleus, respectively. The influence of KF, sex, and age on dynamometric indicators of plantar flexion fatigue was examined in 28 males and 28 females recruited in 2 different age groups (older and younger than 40 years). Each subject performed 50 maximal concentric isokinetic plantar flexions at 60-degree angle per·second with 0° and 45° angles of KF. Maximal voluntary isometric contractions were determined before and after isokinetic trials and maximal, minimal, and normalized linear slopes of peak power during testing. Main effects of and 2-way interactions between KF, sex, age, and order of testing were explored using mixed-effect models and stepwise regressions. At angles of 0° and 45°, the fatigue indicators in younger and older individuals were similar and not influenced by testing order. However, peak isokinetic power and isometric torque declined to greater extents in males than females and, moreover, KF exerted greater impacts on the absolute plantar flexion performance and maximal-to-minimal reduction in isokinetic power in males. Because KF wielded no pronounced effect on fatigue indicators, this test may perhaps be used over time with no major concern regarding the exact knee angle. Our findings indicate that sex, rather than age, should be considered when interpreting dynamometric indicators of fatigue from repeated maximal concentric isokinetic plantar flexions, for example, when establishing normative values or comparing outcomes.

Shortening behavior of the different components of muscle-tendon unit during isokinetic plantar flexions

The torque-velocity relationship has been widely considered as reflecting the mechanical properties of the contractile apparatus, and the influence of tendinous tissues on this relationship obtained during in vivo experiments remains to be determined. This study describes the pattern of shortening of various muscle-tendon unit elements of the triceps surae at different constant angular velocities and quantifies the contributions of fascicles, tendon, and aponeurosis to the global muscle-tendon unit shortening. Ten subjects performed isokinetic plantar flexions at different preset angular velocities (i.e., 30, 90, 150, 210, 270, and 330°/s). Ultrafast ultrasound measurements were performed on the muscle belly and on the myotendinous junction of the medial and lateral gastrocnemius muscles. The contributions of fascicles, tendon, and aponeurosis to global muscle-tendon unit shortening velocity were calculated for velocity conditions for four parts of the total range of motion. For both muscles, the fascicles' contribution decreased throughout the motion (73.5 ± 21.5% for 100-90° angular range to 33.7 ± 20.2% for 80-70°), whereas the tendon contribution increased (25.8 ± 15.4 to 55.6 ± 16.8%). In conclusion, the tendon contribution to the global muscle-tendon unit shortening is significant even during a concentric contraction. However, this contribution depends on the range of motion analyzed. The intersubject variability found in the maximal fascicle shortening velocity, for a given angular velocity, suggests that some subjects might possess a more efficient musculoarticular complex to produce the movement velocity. These findings are of great interest for understanding the ability of muscle-tendon shortening velocity.

Operative Treatment of Chronic Irreparable Achilles Tendon Ruptures With Large Flexor Hallucis Longus Tendon Transfers

Transfer of the flexor hallucis longus (FHL) tendon aims to restore function and relieve pain in chronic Achilles tendon (AT) disease. The goal of the present study was to investigate the clinical and radiographic outcomes of FHL transfer to the AT and to compare the transtendinous technique to the transosseous technique. We hypothesized that the type of technique would have a notable impact on outcome. Forty patients (42 ankles) were retrospectively reviewed and divided into group 1 (transtendinous technique, 22 patients/24 ankles) and group 2 (transosseous technique, 18 patients/18 ankles). Outcome parameters included the American Orthopaedic Foot & Ankle Society (AOFAS) hindfoot score, Victorian Institute of Sports Assessment-Achilles (VISA-A) score, Foot Function Index (FFI), and Short Form-36 (SF-36) scores. Magnetic resonance imaging of the lower leg was performed preoperatively to assess muscle quality and fatty infiltration. Postoperatively, isokinetic plantar flexion strength was assessed using a Con-Trex dynamometer. In group 1 (follow-up, 73 months; age, 52 years), the AOFAS score improved from 66 points to 89 points (P < .001) with average values for the VISA-A of 76 points, FFI-D pain 15%, and FFI-D function 22%. In group 2 (follow-up, 35 months; age, 56 years), the AOFAS score increased from 59 points to 85 points (P < .001) with mean values for the VISA-A 76 points, FFI-D pain 25%, and FFI-D function 24%. At follow-up, the average SF-36 score in group 1 was 66% and in group 2 was 77%. Isokinetic testing at 30 deg/s in group 1 revealed notable weakness in the operated ankle averaging 54.7 N·m (75% of normal), and in group 2 the average was 58.2 N·m (77% of normal). No statistically significant differences were found between the groups. The hypothesis was disproved. Both techniques for FHL transfer to AT, intratendinous and transosseous, provided good to excellent clinical and functional outcome in the treatment of irreparable AT disease. Level III, retrospective comparative series.

The effects of a powered ankle exoskeleton for plantarflexion torque assistance for the elderly

It is necessary to develop a rehabilitation robot for the assistance of movement of the ankle joint and the enhancement of ankle muscular activities during walking for the elderly. A powered ankle exoskeleton with an artificial pneumatic muscle has been designed to provide powered assistance in the plantarflexion motion of the ankle joint. The objective of this study was to confirm the effectiveness of the powered ankle exoskeleton for the plantarflexion torque of the ankle joint. Fifteen healthy and fifteen elderly people used a wearable ankle exoskeleton during the plantarflexion motion of the ankle joint. Participants were assessed with three parameters to confirm the effectiveness of the system: a) maximal voluntary isokinetic plantarflexion torque using a Biodexdynamometer, b) muscular activities of the lower limbs, c) correlation of the agonist muscle and plantar torque during plantarflexion motion of the ankle joint. The assistance of the plantarflexion motion of the ankle joint is determined by the plantarflexion torque of the artificial pneumatic muscle of the powered ankle exoskeleton, and the assistant timing was decided the detection of subject’s movement intention that they did plantarflexion motion of the ankle joint. We developed a muscular stiffness force sensor to detect the activation of the soleus muscle for feed-forward control of the ankle exoskeleton. The experimental results show that the muscular stiffness force of the soleus muscle with feed-forward control was decreased, and the plantarflexion torque of the ankle joint while only wearing the ankle exoskeleton was decreased, but the plantarflexion torque with feed-forward control was increased. The amount of increasing with feed-forward control is higher than that of decreasing only wearing the exoskeleton. Based on the effectiveness of the system with the healthy participants, the elderly may have benefited from the plantarflexion motion augmented by the powered ankle exoskeleton.

The reproducibility of three different indicators of fatigue from plantar-flexion isokinetic testing at two knee flexion angles is not sufficient to be termed 'acceptable'

OBJECTIVE: To characterize the reproducibility of three indicators of fatigue (FIs) specific to concentric plantar-flexion isokinetic testing at knee flexion (KF) angles of 0 ◦ (straight) and 45 ◦ (bent). METHODS: On two separate days one week apart, thirty-four males performed 50 consecutive maximal concentric isokinetic plantar-flexion contractions at 60 ◦ /s with 0 ◦ and 45 ◦ of KF. Differences in the pre- and post-maximal voluntary isometric contraction torques (FIstatic), powers during the initial five and last five isokinetic contractions (FIdynamic) and powers during the 50 isokinetic contractions (FIslope) were used as FIs. Changes in means, intra-class correlation coefficients (ICCs) and coefficients of variations (CVs) were computed to quantify the reproducibility of the FIs. Comparisons were made between the two KF angles and three FIs using two-way repeated measures ANOVA. RESULTS: For both KF angles and three FIs, ICCs ranged from 0.52 to 0.71 and CVs from 10.0 to 29.3%. The CVs from the two isokinetic-based FIs were lower than those from the isometric FI and a trend towards larger ICCs at 0 ◦ was observed. CONCLUSIONS: The reproducibility of the three FIs was not sufficient to be termed ‘acceptable’. The FIslope and FIdynamic were more reproducible than FIstatic and are recommended – with the knee straight rather than bent – until more reliable indicators become available.

Function and Strength Following Gastrocnemius Recession for Isolated Gastrocnemius Contracture

Isolated gastrocnemius contracture (IGC), which limits ankle dorsiflexion with full knee extension, can affect function and quality of life. Gastrocnemius recession is a treatment option for IGC when conservative treatment fails. The goal of this study was to assess range of motion, function, and plantarflexion strength pre- and 3-months post-gastrocnemius recession for subjects with IGC. Ankle range of motion, function, and plantarflexion strength in seven legs (four subjects), clinically diagnosed with IGC, before and after surgery were compared to matched control subjects to elucidate pre- and post-surgical intervention differences. All subjects with IGC were also diagnosed with plantar fasciitis with one leg having an additional diagnosis of metatarsalgia. Subjects with IGC had significant post surgical improvements at 3 months after surgery in dorsiflexion range of motion (p = 0.016), function (p = 0.016) and isokinetic plantarflexion strength (p = 0.018). Surgical recession enhanced range of motion and self reported function while not inducing any detrimental effects to plantarflexion strength at a 3-month followup. Post-surgically IGC subjects were more similar to healthy controls.

Operative Versus Non-Operative Treatment of Achilles Tendon Ruptures: A Randomized Controlled Trial (SS-66)

The purpose of this randomized controlled trial was to compare outcomes of operative and non-operative management of Achilles tendon ruptures. Patients with acute complete Achilles tendon ruptures were randomized to receive open suture repair followed by graduated rehabilitation or graduated rehabilitation alone. The primary outcome measure was re-rupture rate. Assessments at 3 and 6 months, and 1 and 2 years included a modified Leppelhati score (no strength data), range of motion, calf circumference, and isokinetic strength at 1 and 2 years. We report the 2 year findings. Two centres randomized 145 patients (118 males and 27 females), mean age 40.9 ± 8.8 years (22.5 - 67.2) to operative (n=73) and non-operative (n=72) treatment. Fourteen were lost to follow-up. Re-rupture occurred in 3 patients in both groups. The mean modified Leppelhati score (out of 85) was 78.2 ± 7.7 in the operative group and 79.7 ± 7.0 in the non-operative group, which was not significant (-1.5 95%CI −6.4 to 3.5, p=0.55). Mean side-to-side difference in plantar flexion and calf-circumference in the operative group was −2.0 ± 3.2° and −1.4 ± 1.2cm, and in the non-operative group −0.9 ± 3.0°and −1.6 ± 1.8cm respectively. Mean isokinetic plantar flexion strength was 62.4 ± 24.2 for the operative and 56.7 ± 19.3 for the non-operative group, which was not significant (5.7, 95%CI −3.1 to 14.5, p=0.20). There were a greater number of serious adverse events in the operative group, including pulmonary embolus in 1 patient, deep vein thrombosis in 1 and deep infections requiring irrigation and debridement in 3. This study suggests that non-operative management of Achilles tendon ruptures utilizing an accelerated rehabilitation programme may produce comparable results with fewer adverse events.

An assessment of the reliability and standardisation of tests used to elicit reference muscular actions for electromyographical normalisation

Prior to implementing a normalisation method, the standardisation and reliability of the method needs to be examined. This investigation aimed to assess the reliability of EMG amplitudes and test outputs from proposed normalisation methods for the triceps surae. Sixteen participants completed isometric (maximum and sub-maximum); isokinetic (1.05 rad/s, 1.31 rad/s and 1.83 rad/s) squat jump and 20 m sprint conditions, on 3 separate occasions over 1 week. The EMG data was collected from the medial and lateral gastrocnemius (MG and LG) and soleus (SOL). Log transformed typical error measurements (TEM CV%) assessed EMG signal and test output reliability across the three sessions. Only the squat jump provided acceptable EMG reliability for all muscles both between days (SOL: 13%; MG: 14.5%; LG: 11.8%) and between weeks (SOL: 14.5%; MG: 12.9%; LG: 8.9%), with the sprint only showing poor reliability in the LG between days (16.3%). Acceptable reliability for the isometric and isokinetic conditions were muscle and re-test period dependant. Reliable output was found for the squat jump (4.1% and 3.6%), sprint (0.8% and 0.6%) and 1RM plantar flexion test (2.8% and 3.5%) between days and weeks, respectively. Isokinetic plantar flexion displayed poor reliability at all velocities between days and weeks. It was concluded that the squat jump provides a standardised and reproducible reference EMG value for the triceps surae for use as a normalisation method.

The effects of plyometric exercise on unilateral balance performance

The purpose of this study was to determine the effects of plyometric exercise on unilateral balance performance. Nine healthy adults performed baseline measurements on the dominant limb that consisted of: a 20-s unilateral stability test on a tilt balance board, where a higher stability index represented deterioration in balance performance; isokinetic plantar flexion torque at 0.52 and 3.14 rad · s−1; muscle soreness in the calf region; and resting plantar flexion angle. Plyometric exercise consisted of 200 counter-movement jumps designed to elicit symptoms of muscle damage, after which baseline measurements were repeated at 30 min, 24, 48, and 72 h. Perceived muscle soreness of the calf region increased significantly following the plyometric exercise protocol (F4,32 = 17.24, P < 0.01). Peak torque was significantly reduced after the plyometric exercise protocol (F4,32 = 7.49, P < 0.05), with greater loss of force at the lower angular velocity (F4,32 = 3.46, P < 0.05), while resting plantar flexion angle was not significantly altered compared with baseline values (P > 0.05). The stability index was significantly increased (F4,32 = 3.10, P < 0.05) above baseline (mean 2.3, s = 0.3) at 24 h (3.3, s = 0.4), after which values recovered. These results indicate that there is a latent impairment of balance performance following a bout of plyometric exercise, which has implications for both the use of skill-based activities and for increased injury risk following high-intensity plyometric training.

Isokinetic ankle plantarflexion and dorsiflexion strength in patients with rheumatoid arthritis

Backgroud and objectives: In patients with rheumatoid arthritis (RA), some muscle groups are affected in different stages of disease, especially those related to the affected joint. However, data on associations between functional performance and muscle strength in RA are few. Therefore we sought to determine whether isokinetic ankle plantarflexion (PF) and dorsiflexion (DF) strength was affected in RA patients and to study the association between isokinetic strength and other clinical indicators of disability such as walking and stair-climbing time and disease activity in patients with RA. Methods: Thirty three patients diagnosed with RA in the chronic phase were selected from a rheumatology outpatient clinic and matched for age and gender with 33 healthy subjects. Isometric and isokinetic muscle strength was measured in DF and PF. The subjects were also evaluated through the Stanford Health Assessment Questionaire (HAQ), walking and stair-climbing time. Cumulative and current steroid doses (CSD) were calculated. Results: No significant correlations were found between muscle strength and visual analogue scale (VAS) scores, HAQ, ankle involvement, CSD ( p> 0.05). With respect to the isokinetic parameters, no differences have been been observed between RA and control groups ( p> 0.05). Walking and stair-climbing time increased significantly ( p< 0.05) in patients with RA. Conclusions: Ankle isokinetic muscle strength is not affected in inactive RA patients while negative effects of steroids on muscle strength were not demonstrated. Important determinators of walking ability in RA patients should be defined in future studies.

Surgically repaired Achilles tendon ruptures with postoperative mobile ankle cast: a 12-month follow-up study with an isokinetic and a dynamic muscle function test

Seventeen patients (15 men and 2 women) with surgically repaired Achilles tendon ruptures had a mobile cast applied for 6 weeks after the operation that allowed free ankle joint motion. A 12-month follow-up study was performed, with measurements of isokinetic muscle torque in a modified Cybex II dynamometer and a dynamic heel-raise test of muscle fatigue. A majority of the patients were weaker on the treated side in both the isokinetic and the heel-raise tests. The isokinetic plantar flexion torque showed larger differences at an angular velocity of 12°/s than at 90°/s. Seven of the patients in the heel-raise test showed considerable differences between the treated and untreated sides, but our analysis could not explain this with any Certainty.

Surface electromyography and peak torque of repetitive maximum isokinetic plantar flexions in relation to aspects of muscle morphology

This study investigates the relationships between surface electromyography (EMG [Mean frequency of the power spectrum (MNF)]) and peak torque variables obtained during 100 maximum concentric plantar flexions with the right limb at 60° s −1 and different muscle morphological variables. Surface EMG was recorded from the right gastrocnemius lateralis and muscle biopsies were taken from the same site as the EMG electrodes were positioned. Muscle fibre area and fibre type composition were determined on serial muscle cross sections using both histochemistry (myofibrillar adenosine triphosphatase) and immunohistochemistry (monoclonal antibodies against specific myosin heavy chain isoforms). Forty-three female and nine male students participated in the study. Gastrocnemius lateralis contained predominantly type I fibres (50%) and type IIA fibres (40%) in both sexes and large individual differences were found. Principal component analysis (PCA) was used for the intercorrelation analyses, and projection to latent structures (PLS) was used for the multivariate regression analysis. MNF correlated positively with different fibre areas and with the proportion of type I fibres. Fibre areas and sex were the most important factors in the regression of maximum peak torque. High proportion of type I fibres and sex were the most important regressors of peak torque endurance normalised for lean body mass. More studies are needed to understand the complex interrelationships between intrinsic muscle properties and the frequency content of the surface EMG before theoretical models can be formulated that incorporate both fibre areas and fibre type proportions.

Optimal Post-Training Abstinence for Maximal Strength Expression

Tapering commonly precedes strength/power competitions to augment performance, and training abstinence is an extreme manifestation of taper. This study compared the effects of different training-abstinence intervals on several indices of strength. Postresting strength performance was compared in 54 young men who had abstained from a standardized weight training program for either 2, 3, 4, or 5 days. Testing included 1RM heel raise strength and isokinetic plantar flexion peak torque at 1.05 and 3.14 rad · s-1. Heel raise strength was greater at 4 days as compared to 2 or 5 days, whereas performance at 3 days was no different (p > .05) than any of the other rest intervals. Isokinetic plantar flexion peak torque at both 1.05 and 3.14 rad · s-1 was unaffected by any of the rest intervals. Small to moderate effect sizes were found for heel raise strength for groups resting 3 and 4 days as well as for slow and fast isokinetic peak torque for the group resting 4 days. It was concluded that a transient elevation in heel raise strength in young men appears to occur by the fourth day of abstinence from heavy-resistance heel-raise training. Under the same experimental conditions, it appears that a modest increase in both slow and fast isokinetic plantar-flexion strength may also occur.

EXERCISE PERFORMANCE AND GASTROCNEMIUS MUSCLE CHARACTERISTICS IN PERIPHERAL ARTERIAL DISEASE

PURPOSE We aimed to measure whole body exercise capacity (walking and cycling), local calf muscular strength and endurance, and various morphological characteristics of the medial gastrocnemius muscle in 16 PAD patients (age: 63 y, BMI: 25.9) and 13 healthy control (CON) subjects (age: 62, BMI 25.9). METHODS Whole body exercise capacities were measured with incremental treadmill and cycle tests. Calf strength was measured as peak force on an isokinetic dynamometer, and calf endurance was measured using an incremental isokinetic plantar flexion protocol. A resting muscle sample was taken from the medial gastrocnemius of the most diseased limb (that with the lowest ankle: brachial systolic pressure index) in the PAD patients and a randomly chosen limb in the CON subjects, and it was analysed histochemically for fibre type, fibre area, capillary to fibre ratio, capillary contacts per fibre and the relative optical density of glycogen per fibre. RESULTS Whole body and local calf muscle exercise performance was 25–59% lower in the PAD patients compared with CON. PAD patients had a relatively greater proportion of type IIA (PAD:27%; CON:16%) and lower proportion of type I (PAD: 49%; CON:62%) muscle fibres, fewer capillaries per fibre (PAD:1.63; CON:2.12), and tended to have smaller fibre areas (^10%). In PAD patients only, muscle strength, area of all three fibre types, capillary contacts with type I and IIA fibres, and the relative optical density of glycogen in type I fibres were positively correlated (P less than 0.05) with treadmill and cycling performance. CONCLUSION These data suggest that a low muscle capillary supply, fibre area and glycogen content in type I fibres are related to exercise intolerance in PAD, and confirms that low calf muscle strength is also an aspect of exercise intolerance in this clinical population.

Rerupture and deep infection following treatment of total Achilles tendon rupture.

The incidence of total Achilles tendon rupture has increased, but we are not aware of any reports on the incidence of reruptures or deep infections following treatment. The outcome after successful treatment is good, but that after complications has not been well documented. A group of 409 patients with a complete Achilles tendon rupture was treated at a university hospital orthopaedic unit between 1979 and 2000. Twenty-three reruptures (prevalence, 5.6%) and nine deep infections (prevalence, 2.2%) occurred in twenty-nine patients. We retrospectively reviewed the records of these patients to determine the overall incidence of ruptures, reruptures, and deep infections and to record the known risk factors for these major complications. We analyzed the final clinical outcome for twelve patients with a rerupture and seven patients with a deep infection at a mean of 4.1 years after the initial treatment. The annual incidence of reruptures (per 100,000 inhabitants) increased from 0.25 in 1979-1990 to 1.0 in 1991-2000, and that of deep infections increased from 0 in the 1980s to 0.63 in the 1990s. The ratio of complications to primary ruptures did not change. The patients with deep infections were significantly older, received corticosteroid medication more often, had sustained the tendon injury during everyday activities more often, and had a longer delay before treatment than the patients with simple reruptures. At 4.1 years after the primary treatment, eight of twelve patients in the rerupture group had a satisfactory clinical outcome and the overall average isokinetic plantar flexion strength deficit in that group was only 10%. In contrast, two of the patients in the infection group had a fair clinical outcome and five had a poor outcome, and the average isokinetic plantar flexion strength deficit in that group was 35%. The incidence of Achilles tendon reruptures and deep infections has increased. The outcome is satisfactory after a simple rerupture without infection, but the results after a deep infection are often devastating.

Measuring Lower Extremity Strength in Older Adults: The Stability of Isokinetic versus 1RM Measures

In order to obtain joint-specific baseline strength characteristics in older adults, clinicians and researchers must have knowledge regarding the relative stability of the various strength tests (the strength difference between repeated measures) and the number of prebaseline practice sessions required to obtain consistent data. To address these needs, the relative multiple-test stability and reliability associated with lower extremity isokinetic and 1-repetition-maximum (1RM) strength measures were assessed in a sample of older adults (N= 30, 65.2 ± 6.3 years), over 4 weeks (T1-T4). Isokinetic ankle plantar-flexion (30°/s) strength and 1RM ankle plantar-flexion, leg-press, and knee-flexion strength exhibited poor stability between Weeks T1 and T2 but stabilized between Weeks T2 and T3 and Weeks T3 and T4. The measures exhibited low incidence of injury and induced low levels of residual muscle soreness. Findings suggest that the 1RM measures require at least 1 prebaseline training session in order to establish consistent baseline performance and are more reliable than isokinetic ankle plantar-flexion tests.

Exercise Performance, Functional Status, and Hemodynamic Assessment of Elderly Patients with Intermittent Claudication

Peripheral arterial disease (PAD) is associated with impaired lower extremity function. This study investigated differences in PAD and control participants and the relationship between lower limb strength and clinical measures of PAD severity. Participants were evaluated by 6-min-walk distance, normal and maximal walking speed over 10 m, isometric plantar-flexion strength, and dynamic dorsi-/plantar-flexion strength. Hemodynamic measures of the lower limbs were recorded at rest and after maximal treadmill testing. PAD participants walked significantly less far during the 6-min walk, and there were large differences in normal and maximal walking speeds. Small to moderate differences were found for isometric plantar-flexion strength. In the diseased legs of the PAD participants, resting systolic hallux photoplethysmography was significantly correlated with isokinetic plantar-flexion strength and onset of claudication pain during the 6-min-walk test. In addition to confirming the documented loss of walking endurance, these data suggest that loss of strength of the plantar flexors is associated with increasing PAD impairment.

The test-retest reliability of concentric and eccentric muscle action during plantar flexion of the ankle joint in a closed kinetic chain

Maximum concentric and eccentric isokinetic plantar flexion peak torque values were evaluated in a closed kinetic chain in eight volunteers from a high-level junior soccer team, with a median age of 17 (range 16-18) years. An isokinetic dynamometer was used and the reproducibility of a previously unevaluated position of the subject was assessed. The test-retest interval was 48 hours. The reproducibility of the test was high, with Intraclass Correlation Coefficients (ICC) of 0.87-0.97 for right- and left-sided concentric and eccentric recordings. The mean peak torque generation was significantly higher in eccentric muscle action compared with concentric; 324 (SD 107) vs 177 (SD 55) Nm. We conclude that one valuable method for measurements of plantar flexion torque in the ankle joint could be in the closed kinetic chain position.

Quantifying synergist activation patterns during maximal plantarflexion using an orthogonal expansion approach

This study sought to determine how well a pattern-recognition approach based on orthogonal-expansion theory can quantify patterns of activation amplitudes that have been recorded by electromyography (EMG) from synergist muscles during isokinetic plantarflexion. Raw surface EMG data were recorded from six muscle sites – four over the agonist Triceps Surae (Lateral and Medial Gastrocnemius, a lateral and a medial site over the Soleus) and two over the antagonist Tibialis Anterior (upper and lower sites) muscles – in ten healthy subjects as they performed three maximal plantarflexor efforts against an isokinetic dynamometer at each of three angular-velocity settings (90 trials). After the root-mean-square amplitude had been calculated for each EMG recording and had been normalized to the amplitude measured during a maximal voluntary isometric contraction, the mean normalized amplitudes were calculated for each muscle site, for the 90 trials. The differences among the muscles and the variability in the normalized amplitudes indicated that the sample mean did not characterize the patterns of relative activation amplitudes among the six muscle sites for all subjects, trials and conditions. An eigenvector decomposition of the normalized data yielded a set of vectors that represents the principal patterns of the activation amplitudes. The principal pattern reflected by eigenvector 1 was 0.57, 0.49, 0.47, 0.45, 0.12 and 0.06 corresponding to the Lateral and Medial Gastrocnemius, the lateral and medial Soleus sites, and the upper and lower sites on the Tibialis Anterior, respectively. The percent trace for eigenvector 1 was 94%; however, two or three eigenvectors were needed to characterize the patterns for some trials. Since 99% of the variance was accounted for by three eigenvectors, the approach was effective in reducing the data while maintaining the salient features in the synergistic patterns of activation amplitudes during isokinetic plantarflexion. PsycINFO classification: 2330; 2530

REPRODUCIBILITY OF ISOMETRIC AND ISOKINETIC TESTING OF ANKLE PLANTAR FLEXION STRENGTH AND ENDURANCE

142 Use of isometric and isokinetic strength measurements has helped many athletic trainers, exercise physiologists, physical therapists, and others to reliably measure voluntary production of force, power, torque and work. Although there have been ample studies concentrated on the knee, quadriceps, shoulder, and back, the reliability of the ankle has not been well studied. The purpose of this research was to conduct reproducible strength measurements of ankle plantar flexion over a 10 week period. Seven healthy subjects, ranging in physical activity from moderate to active, were studied. The subjects were tested on three different occasions: week 1 (W1), week 5 (W5), and week 10 (W10). The neutral position (0 °) was set at a 90 ° angle between the foot and the tibia. Maximal isometric strength was tested with the ankle at the defined 0 ° neutral position and at 10 ° plantar flexion. Maximal voluntary contractions (MVCs) were performed for 5 seconds. Isokinetic contractions were performed between the neutral position and the maximal plantar flexion position that the subjects experienced as being comfortable. Isokinetic strength was measured at angular velocities of 30, 60, 120 and 180 degrees/sec. Maximal isokinetic endurance was tested by monitoring fatigue and total work done over 50 repeated isokinetic plantar flexions at 60 °/sec. ANOVA statistics showed little variation between isometric and isokinetic measurements taken at each time point. The average p-value of isometric and isokinetic plantar flexion was 0.0039±0.0012 and 0.0791±0.0415, respectively. The isokinetic endurance test, however, showed a significant amount of variance between time points; ANOVA p-values in peak torque and work were 0.7779±0.1300 and 0.5549±0.1182, respectively. This study suggests that measurement of isometric and, to a lesser extent, isokinetic MVCs can potentially be used as a reliable, diagnostic tool to monitor patients' rehabilitation and recovery of strength following ankle joint trauma, disuse and consequent skeletal muscle atrophy in surrounding plantar flexors.