Isokinetic Plantar Research Articles

Combined effect of contraction type and intensity on corticomuscular coherence during isokinetic plantar flexions.

During isometric contractions, corticomuscular coherence (CMC) may be modulated along with the contraction intensity. Furthermore, CMC may also vary between contraction types due to the contribution of spinal inhibitory mechanisms. However, the interaction between the effect of the contraction intensity and of the contraction type on CMC remains hitherto unknown. Therefore, CMC and spinal excitability modulations were compared during submaximal isometric, shortening and lengthening contractions of plantar flexor muscles at 25, 50, and 70% of the maximal soleus (SOL) EMG activity. CMC was computed in the time-frequency domain between the Cz EEG electrode signal and the SOL or medial gastrocnemius (MG) EMG signals. The results indicated that beta-band CMC was decreased in the SOL only between 25 and 50-70% contractions for both isometric and anisometric contractions, but remained similar for all contraction intensities in the MG. Spinal excitability was similar for all contraction intensities in both muscles. Meanwhile a divergence of the EEG and the EMG signals mean frequency was observed only in the SOL and only between 25 and 50-70% contractions, independently from the contraction type. Collectively, these findings confirm an effect of the contraction intensity on beta-band CMC, although it was only measured in the SOL, between low-level and high-level contraction intensities. Furthermore, the current findings provide new evidence that the observed modulations of beta-band CMC with the contraction intensity does not depend on the contraction type or on spinal excitability variations.

Isokinetic Plantar Flexion Endurance. Reliability and Validity of output/excitation Measurements

The reliability and validity of isokinetic measurement of plantar flexion endurance has been studied by a method previously described by us which utilizes simultaneous measurements of mechanical contractional work (CW) and integrated electromyogram (iEMG). The reliability was gauged by test/re-test with a two year's interval; while validity was assessed by myoelectric power spectrum analyses. The output/input balance (CW/iEMG) remained unchanged for the group as well as inter-individually. Changes in myoelectric power spectrum as function of number of contractions were clearly indicative of fatigue. Under the present conditions fatigue of fast twitch motor units may explain the rapid decreases in output and excitation followed by nearly steady state levels of all registered parameters. As is the case for non-fatigued isokinetic plantar flexions, the motor unit recruitment order appears quite stereotyped during plantar flexion fatigue. The findings of significantly lower mean power spectrum during the first part of each contraction than during the second part may support the size-principle described by Henneman.

Tendon Length, Calf Muscle Atrophy, and Strength Deficit After Acute Achilles Tendon Rupture: Long-Term Follow-up of Patients in a Previous Study.

In this prospective study, we used magnetic resonance imaging (MRI) to assess long-term Achilles tendon length, calf muscle volume, and muscle fatty degeneration after surgery for acute Achilles tendon rupture. From 1998 to 2001, 60 patients at our center underwent surgery for acute Achilles tendon rupture followed by early functional postoperative rehabilitation. Fifty-five patients were reexamined after a minimum duration of follow-up of 13 years (mean, 14 years), and 52 of them were included in the present study. Outcome measures included Achilles tendon length, calf muscle volume, and fatty degeneration measured with MRI of both the affected and the uninjured leg. The isokinetic plantar flexion strength of both calves was measured and was correlated with the structural findings. The Achilles tendon was, on average, 12 mm (95% confidence interval [CI] = 8.6 to 15.6 mm; p < 0.001) longer (6% longer) in the affected leg than in the uninjured leg. The mean volumes of the soleus and medial and lateral gastrocnemius muscles were 63 cm (13%; p < 0.001), 30 cm (13%; p < 0.001), and 16 cm (11%; p < 0.001) lower in the affected leg than in the uninjured leg, whereas the mean volume of the flexor hallucis longus (FHL) was 5 cm (5%; p = 0.002) greater in the affected leg, indicating FHL compensatory hypertrophy. The median plantar flexion strength for the whole range of motion ranged from 12% to 18% less than that on the uninjured side. Finally, the side-to-side difference in Achilles tendon length correlated substantially with the strength deficit (ρ = 0.51, p < 0.001) and with medial gastrocnemius (ρ = 0.46, p = 0.001) and soleus (ρ = 0.42, p = 0.002) muscle atrophy. Increased Achilles tendon length is associated with smaller calf muscle volumes and persistent plantar flexion strength deficits after surgical repair of Achilles tendon rupture. Strength deficits and muscle volume deficits are partly compensated for by FHL hypertrophy, but 11% to 13% deficits in soleus and gastrocnemius muscle volumes and 12% to 18% deficits in plantar flexion strength persist even after long-term follow-up. Therapeutic Level II. See Instructions for Authors for a complete description of levels of evidence.

Effects of Plyometric Training on Rock’n’Roll Performance

Objectives: The aim of the study was to analyse if plyometric training increases the sport specific performance in rock’n’roll dancers. Design: Fifteen semi-professional rock’n’roll dancers participated in a plyometric training study. Pre- and posttests were conducted to document alterations of sport specific performance, reactive strength as well as maximal isokinetic torque. Method: The participants (n=15) accomplished two training sessions weekly for a training period of 6 weeks. The training program consisted of different of jumps. Pre- and posttests included a rock’n’roll specific performance test examining the maximal number of kicks within 30 s. Moreover, jumping height and ground contact time (GCT) during drop jump were determined to calculate reactive strength (RSI). Maximal dynamic torque and work were determined during maximal isokinetic contractions of the plantar flexors. Results: The number of kicks increased from 46.5 ± 2.6 to 49.4 ± 2.7 (p=0.00, d Z =1.83).The RSI increased significantly from 2.57 ± 0.29 to 2.72 ± 0.44 (p=0.05, d Z =0.55). The gains of RSI are based on increases in jumping height (pretest: 24.6 ± 4.0 cm, posttest 26.5 ± 4.7 cm, p=0.01, d Z =0.71), whereas the GCT remained unaltered (p=0.53). The work during maximal isokinetic plantar flexions increased significantly in both legs (jumping leg: p = 0.04, d Z =0.58; kicking leg: p=0.05, d Z =0.55). Conclusions: Plyometric training increases the kicking frequency during rock’n’roll dance. This might be attributed to the observed increase in reactive strength. Training induced changes in muscle activity or structure were discussed. It is suggested to implement plyometric training into the training program of rock’n’roll dancers. Keywords: Rock’n’roll, plyometric training, reactive strength, plantar flexors

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.

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.

Agonist and antagonist strength of ankle musculature in basketball players aged 12 to 17 years

Muscle strength and balance around the lower limb joints may play an important role for performance and injury prevention in basketball. The purpose of this study was to examine isokinetic functional and conventional torque ratios around the ankle joint in young basketball players. One hundred and eighty males from 12 to 17 years old (30 persons per age group) performed maximum concentric and eccentric efforts of the plantar and dorsiflexors at 30 ◦ ·s −1 and 90 ◦ ·s −1 . Three-way analysis of variance (ANOVA) designs indicated that the absolute isokinetic plantar and dorsiflexion strength increased ( p< 0.05) from 12 to 15 years and then demonstrated a plateau until 17 years old. When the isokinetic strength was normalized relative to body mass the only difference was found between the 16-17 and 12-13 year-olds. Two-way ANOVAs indicated non-significant effects of chronological age on all reciprocal muscle group ratios suggesting uniformity in the development of peak isokinetic torque of plantar and dorsiflexors throughout the developmental ages. Coaches and physical therapists may use this information when evaluating and planning exercise programs of ankle musculature during training and rehabilitation.

Automated moving fluoroscope: a novel method to acquire video fluoroscopic data during level walking

Broström E, Nordlund MM, Cresswell AG. Plantar- and dorsiflexor strength in prepubertal girls with juvenile idiopathic arthritis. Arch Phys Med Rehabil 2004;85:1224–30.To compare lower-leg strength of young girls with polyarticular juvenile idiopathic arthritis (JIA) with that of healthy, age-matched controls.Isometric and isokinetic strength tests of the plantar- and dorsiflexors. All strength measures were made at an ankle angle of 90°. Isokinetic plantar- and dorsiflexor measures were made at 15°/s during shortening (concentric) and lengthening (eccentric) actions.Strength testing laboratory.Ten prepubertal girls diagnosed with JIA and 10 healthy girls.Not applicable.Isometric and isokinetic plantar- and dorsiflexor strength.Isometric plantar- and dorsiflexion torques were significantly lower (48% and 38% respectively; P<.05) for the children with JIA than for the controls. The JIA group also produced lower shortening plantarflexion torques (52%, P<.05). Lengthening plantarflexor torques did not differ significantly between the 2 groups (P<.05). Controls were stronger than the JIA group for both shortening and lengthening maximal dorsiflexor actions (P<.05). All children were 4 to 5 times stronger in plantarflexion than in dorsiflexion.Girls with JIA had significantly less plantar- and dorsiflexor strength than age-matched, healthy peers. The reduced strength of children with JIA is likely to affect function in daily activities and probably contributes to reduced levels of physical activity.

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.

Plantar- and dorsiflexor strength in prepubertal girls with juvenile idiopathic arthritis 1,2

Broström E, Nordlund MM, Cresswell AG. Plantar- and dorsiflexor strength in prepubertal girls with juvenile idiopathic arthritis. Arch Phys Med Rehabil 2004;85:1224–30. Objective To compare lower-leg strength of young girls with polyarticular juvenile idiopathic arthritis (JIA) with that of healthy, age-matched controls. Design Isometric and isokinetic strength tests of the plantar- and dorsiflexors. All strength measures were made at an ankle angle of 90°. Isokinetic plantar- and dorsiflexor measures were made at 15°/s during shortening (concentric) and lengthening (eccentric) actions. Setting Strength testing laboratory. Participants Ten prepubertal girls diagnosed with JIA and 10 healthy girls. Interventions Not applicable. Main outcome measures Isometric and isokinetic plantar- and dorsiflexor strength. Results Isometric plantar- and dorsiflexion torques were significantly lower (48% and 38% respectively; P<.05) for the children with JIA than for the controls. The JIA group also produced lower shortening plantarflexion torques (52%, P<.05). Lengthening plantarflexor torques did not differ significantly between the 2 groups ( P<.05). Controls were stronger than the JIA group for both shortening and lengthening maximal dorsiflexor actions ( P<.05). All children were 4 to 5 times stronger in plantarflexion than in dorsiflexion. Conclusions Girls with JIA had significantly less plantar- and dorsiflexor strength than age-matched, healthy peers. The reduced strength of children with JIA is likely to affect function in daily activities and probably contributes to reduced levels of physical activity.

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.

A method of measuring standing isokinetic plantar and dorsiflexion peak torques

Different methods have been used for concentric (CONC) isokinetic testing of ankle dorsiflexion (DF) and plantar flexion (PF). However, little information is available on either the reliability of these protocols or eccentric (ECC) torque production. As well, previous studies utilized non-weight-bearing test positions. The purpose of this study was to develop a reliable method of testing CONC and ECC DF and PF in a weight-bearing position. One group of adults, including older men and women were tested on two occasions with a standing protocol. Another group of older and younger men and women were compared between the standing method and a supine protocol. For both positions the velocity was 30 degrees.s-1 for the CONC and ECC actions, and the range of motion was 10 degrees DF to 20 degrees PF. Reliability coefficients for peak torque (PT) were acceptable and ranged from 0.65 to 0.90. The two testing positions were significantly related (r = 0.84-0.91), but CONC PT in standing were greater than supine. Therefore, this method of testing isokinetic DF and PF in a standing position has acceptable reliability and produces results consistent with those acquired with the supine protocol. It provides a means of comparing groups and examining intervention strategies while weight-bearing.

Comparison of Functional Ability Following Percutaneous and Open Surgical Repairs of Acutely Ruptured Achilles Tendons

The purpose of our study was to evaluate the functional outcomes of two methods of surgical treatment of acute closed raptures of the Achilles tendon, specifically, the primary open repair and the percutaneous repair techniques, utilizing (a) isokinetic plantar flexion strength, (b) midcalf girth, (c) ankle joint proprioception, and (d) ankle range of motion values. As a secondary purpose, the frequency of reruptures and postsurgical complications were compared between techniques. Twenty male patients (mean age, 43.8 ± 9.4 years) who sustained complete, closed ruptures of the Achilles tendon participated in this study. Results of pairedttests revealed significant differences between postsurgical and contralateral normal limbs for 6 of 12 variables. Results of the ANOVAs revealed no significant differences between the open repair group and percutaneous repair group for any of the evaluative parameters. The significant deficits in postoperative isokinetic plantar flexion strength and midcalf girth measurements, irrespective of surgical technique, suggest an incompleteness of rehabilitation or, more likely, the physiological inability to regain these characteristics postoperatively.

Is the mean power frequency shift of the EMG a selective indicator of fatigue of the fast twitch motor units?

During repeated maximum isokinetic contractions parallel decreases in output and the mean power frequency (MPF) of the electromyogram (EMG) occur, followed by stable levels (the endurance level). This study aimed to investigate if hypoxia of the plantar flexors will result in a shift in MPF during the endurance level. Mechanical performance and simultaneous surface EMG activity of three plantar flexors (m. soleus, m. gastrocnemius medialis and m. gastrocnemius lateralis) were recorded during repeated isokinetic plantar flexions at 1.05 rad s-1 in 10 healthy women. The study consisted of two tests with 14 days in between: (1) a maximum test consisting of 125 maximum plantar flexions. After 100 contractions, using a tourniquet, a relative ischaemia (hypoxia) was induced. (2) a submaximum test performed at the level established between contractions 70-100 of the maximum test, consisting of 125 plantar flexions. During the maximum test mechanical performance output, the signal amplitude (RMS) of the EMG and the MPF decreased in parallel during the initial 50 contractions followed by stable levels during the subsequent 50 contractions. When hypoxia was induced decreases in mechanical performance and RMS appeared without significant decreases in MPF. The present study indicates that the MPF shift is mainly sensitive to biochemical changes in the type 2 fibres. Hypoxia mainly located to the type 1 fibres will not be detected using the MPF variable.

Mechanical output and iEMG of single and repeated isokinetic plantar flexions: a study of untrained and endurance-trained women.

Isokinetic plantar flexion peak torque (PT), contractional work (CW), and integrated electromyographic activity (iEMG) were analyzed in a group of untrained females and a group of female elite orienteers. Similar levels of PT, CW, and iEMG were observed in both groups during single maximum maneuvers (30-180 degrees s1). During repetitive (200) maximum plantar flexions, the untrained females showed a steeper and more pronounced decline in CW during the first 50 contractions than the orienteers. After this fatigue phase, all subjects could maintain a steady-state level of CW throughout the test. This level of CW was significantly (20%) higher in the orienteers than in the untrained females. The iEMGs of the gastrocnemii and soleus muscles decreased to significantly (10%) lower levels in the untrained women than in the orienteers. For both groups, the soleus muscle showed a significantly higher steady-state level of iEMG (10%) than mm. gastrocnemii. In the untrained group, CW/iEMG of m. triceps surae decreased to a plateau level significantly lower than in the orienteerers who could virtually maintain the initial CW/iEMG throughout the test. The differences observed could be explained by adaptations to performed endurance training in the orienteers.

Relationship between work and electromyographic activity during repeated leg muscle contractions in orienteers.

Contraction work (CW) was recorded for each of 200 repetitive isokinetic plantar flexions (1.05 rad.s-1) and knee extensions (1.57 rad.s-1) in 14 elite male orienteers. Simultaneous recordings of integrated electromyograms (iEMG) were obtained from the 3 parts of triceps surae and from 3 superficial portions of quadriceps femoris. CW in both muscle groups decreased significantly during the first 30 contractions (the fatigue phase), followed by a steady state level. The relative steady state level was higher for the plantar flexors (70 +/- 17%) than for the knee extensors (56 +/- 12%). For quadriceps a significant increase in iEMG occurred during the first 10 contractions followed by a decrease, whereas the iEMG of the plantar flexors showed a gradual decrease to the steady state level, which was similar for the two muscle groups (71-72%). The chosen expression of output/input balance (CW/iEMG) was constant throughout the plantarflexion test but decreased during the initial 20 knee extensions down to 82%. Thus, the fatigue phase of the knee extensions appeared to be divided into two; the first part had decreases in both CW and CW/iEMG and the second part with a decrease in CW alone. In contrast the plantar flexors only showed the characteristics of the second part.

Repeated isokinetic plantar flexions at different angular velocities.

Peak torque (PT), contraction work (CW) and mean power (CP) were measured for each of 200 repetitive isokinetic (maximum effort) plantar flexions. Simultaneous recording of integrated electromyograms (iEMG) were obtained from the three parts of the triceps surae muscle. Four tests at different angular velocities (30, 60, 120 and 180 degrees s-1 (degrees X s-1] were performed with at least 2 weeks between each test. The subjects were eight clinically healthy females (24-36 years). At all four angular velocities CW, CP and PT decreased steeply during the first approximately 70 contractions, followed by a steady-state level with no further significant decreases. The relative decreases of PT and CP were significantly smaller than for CW at all velocities. The relative CW decline increased with angular velocity; the relative PT and CP decreases were not velocity dependent. Also iEMG activity decreased in two phases during the 200 contractions and were on a significantly lower relative level at 180 degrees X s-1. However the reduction of range of motion was significantly greater at 180 degrees X s-1 and when the iEMG activity was compensated for this decrease the relative decreases in electromyographic activity were similar at the four angular velocities. The results indicated that CW was more sensitive to fatigue than PT and CP and that CW fatigue was dependent on angular velocity.

Mean power frequency and integrated electromyogram of repeated isokinetic plantar flexions.

Peak torque (PT), contraction work (CW), mean power (CP), and time for contraction (t) were recorded for each of 200 full range-of-motion repetitive isokinetic (maximum effort) plantar flexions at the preset angular velocity 60 degrees s-1 (degrees X s-1). The subjects were 12 healthy males (42-46 years). Simultaneous recordings of electromyographic activity of the three parts of the triceps surae muscle were made. The electromyograms were truly integrated and the mean power frequency was also calculated for each of the contractions. The mechanical variables decreased steeply during approximately the first 70 contractions (the fatigue phase) followed by a steady-state level (the endurance level) with no further significant decrease. The fatigue phase was composed of two parts. The first was characterized by decreases in CW, MPF and in the ratio CW/iEMG, while iEMG and iEMG/t were unaltered. During the second part decreases in iEMG and iEMG/t occurred while MPF and CW/iEMG had stabilized. During the endurance level all the variables were stable but lowered when compared with the initial contractions of the fatigue phase. The results indicated that the mechanical fatigue went through two parts before the steady-state level was established.

Prediction of peak torque and contraction work at different isokinetic angular velocities of plantarflexion.

Contraction work (CW) and peak torque (PT) of maximum isokinetic plantar flexions were measured in clinically healthy subjects randomly chosen from the official census list of Umeå, Sweden, in three groups: 40-44, 50-54 and 60-64 years of age, with similar proportions of men and women. Maximum isokinetic plantar-flexions were performed at angular velocities of 30, 60, 120 and 180 degrees X s-1. Body-weight, height and crural circumference were measured. Subjects rated their levels of leisure and occupational activities. To establish formulae to predict CW and PT, stepwise regression procedures were applied. The predictive powers (r2) of the formulae which incorporated age, sex and crural circumference, were higher for PT (30 degrees X s-1: 0.82, 60 degrees X s-1: 0.79, 120 degrees X s-1: 0.75, 180 degrees X s-1: 0.56) than for CW (30 degrees s-1: 0.63, 60 degrees s-1: 0.63, 120 degrees s-1: 0.60, 180 degrees s-1: 0.52). Thus the part of the variance explained decreased with increasing angular velocity, but more than 50% was still explained at 180 degrees s-1. The results indicate that the mechanical output of the plantar flexors is predictable.