Specificity of power improvements through slow and fast isokinetic training

Inter-limb interactions and constraints in the expression of maximum force: a review, some implications and suggested underlying mechanisms

Human motor action in both sporting and industrial situations involves complex movement patterns that require the concurrent activation of more than one unit of the motor system. This paper is about one aspect of how different muscle groups affect each other when they are activated in unison. Twenty years of research suggests that the maximum force-generating capacity of human muscles varies according to whether they contract alone or with other muscles. An example of this is the 'bilateral deficit' phenomenon (Ohtsuki, 1983), whereby the force produced when individuals perform simultaneous bilateral contractions of homologous limbs is less than the sum of the forces produced when each of the limbs contracts alone. The implications of investigations examining force-related patterns of inhibition in multi-limb action have been largely ignored and no serious attempt has hitherto been made to establish a theoretical framework within which to accommodate the findings. This paper reviews literature addressing the question of inter-limb inhibition in the expression of maximum force and discusses some of the implications that arise. A proposal is made that inter-limb interference can be accounted for in terms of the neural interconnectedness of cerebral control areas and suggestions made to show how the findings of previous research can be accommodated within contemporary neurobehavioural models of human performance.

The effects of periodized velocity-specific resistance training on maximal and sustained force production in women

The purpose of this study was to assess the effects of slow, fast or periodized slow and fast resistance training on voluntary, maximal and sustained force production. Altogether, 34 active females were pre-tested for maximal force production (MXF) and 20-repetition mean force production (MNF) at 1.05 and 3.14 rad s-1 (60 and 180 deg s-1). They were then randomly placed into one of four groups: group S trained for 8 weeks at 1.05 rad s-1, group F trained for 8 weeks at 3.14 rad s-1, group P trained for 5 weeks at 1.05 rad s-1 and 3 weeks at 3.14 rad s-1, while group C acted as the controls. Groups S, F and P demonstrated significant increases in MXF and MNF at 1.05 and 3.14 rad s-1. The increases in MXF were similar between the trained groups, whereas groups S and P demonstrated significantly greater increases in MNF than group F at 1.05 rad s-1 and group P exhibited significantly greater increases in MNF than group S at 3.14 rad s-1. These results suggest that, regardless of training velocity, similar increases in MXF are produced at 1.05 and 3.14 rad s-1, whereas periodized slow and fast resistance training may produce greater increases in MNF than slow or fast training alone.

Neuromuscular adaptations during the acquisition of muscle strength, power and motor tasks

Neuromuscular performance is determined not only by the size of the involved muscles, but also by the ability of the nervous system to appropriately activate the muscles. Adaptive changes in the nervous system in response to training are referred to as neural adaptation. This article briefly reviews current evidence regarding the neural adaptations during the acquisition of muscle strength power and motor tasks and will be organized under four main topics, namely: (i) muscle strength gain: neural factors versus hypertrophy, (ii) neural adaptations during power training, (iii) neuromuscular adaptations during the acquisition of a motor task, and (iv) neuromuscular adaptations during a ballistic movement.

Biomechanics of sprint running. A review

Understanding of biomechanical factors in sprint running is useful because of their critical value to performance. Some variables measured in distance running are also important in sprint running. Significant factors include: reaction time, technique, electromyographic (EMG) activity, force production, neural factors and muscle structure. Although various methodologies have been used, results are clear and conclusions can be made. The reaction time of good athletes is short, but it does not correlate with performance levels. Sprint technique has been well analysed during acceleration, constant velocity and deceleration of the velocity curve. At the beginning of the sprint run, it is important to produce great force/power and generate high velocity in the block and acceleration phases. During the constant-speed phase, the events immediately before and during the braking phase are important in increasing explosive force/power and efficiency of movement in the propulsion phase. There are no research results available regarding force production in the sprint-deceleration phase. The EMG activity pattern of the main sprint muscles is described in the literature, but there is a need for research with highly skilled sprinters to better understand the simultaneous operation of many muscles. Skeletal muscle fibre characteristics are related to the selection of talent and the training-induced effects in sprint running. Efficient sprint running requires an optimal combination between the examined biomechanical variables and external factors such as footwear, ground and air resistance. Further research work is needed especially in the area of nervous system, muscles and force and power production during sprint running. Combining these with the measurements of sprinting economy and efficiency more knowledge can be achieved in the near future.

Physiological adaptations to velocity-controlled resistance training

The force-velocity characteristics of skeletal muscle are such that maximal force is inversely related to the velocity of shortening. This relationship has been observed using isolated muscle preparations and intact muscle groups (e.g. knee extensors). Isokinetic dynamometry has revealed some specific physiological adaptations to different velocities of training: an increase in torque and power that are greater at or near the velocity of training; a transfer of torque gains to slower and faster angular velocities after intermediate velocity resistance training; increases in maximal oxygen consumption and cardiac output in response to circuit training; increases in anaerobic power output; changes in skeletal muscle size and changes in myofibrillar ATPase activity; and new applications for rehabilitation of muscular and ligamentous injuries, and post-coronary patients.

Effect of one-legged exercise on the strength, power and endurance of the contralateral leg. A randomized, controlled study using isometric and concentric isokinetic training

The purpose of this investigation was to study the effect of one-legged exercise on the strength, power and endurance of the contralateral leg. The performance of the knee extensor and flexor muscle of 20 healthy young adults (10 men and 10 women) was first tested by Cybex II+ and 340 dynamometers. Then 10 subjects were chosen at random to train using one leg three times a week for 7 weeks whilst the other 10 served as controls. During the 8th week, the tests were repeated. Both quadriceps and hamstring muscles of the trained subjects showed a cross-transfer effect from the trained limb to the untrained side. This concerned the strength and power, as well as endurance characteristics of these muscles. The average change in peak torque of the quadriceps muscle was +19% (P less than 0.001) in the trained limb, +11% (P less than 0.01) in the untrained limb and 0% in the control limbs. In hamstring muscles the changes were +14% (P less than 0.01), +5% and -1%, respectively. Concerning muscle endurance (work performed during the last 5 contractions in the 25-repetition test) the corresponding changes were +15% (P less than 0.01), +7% (P less than 0.01), and -1% in quadriceps muscle, and +17% (P less than 0.05), +7%, and -3% in hamstring muscles. The average strength benefit in the untrained limb was +36% (hamstring muscles) and +58% (quadriceps muscle) of that achieved in the trained limb. Untrained hamstring muscle showed better benefits in the endurance parameters than in strength or power parameters, while in the quadriceps muscle this effect was reversed. A positive relationship was observed between the changes (greater improvement in the trained limb resulted in greater improvement in the untrained limb) (hamstring muscles: r = 0.83, P less than 0.001, quadriceps muscle: r = 0.53, P less than 0.001). In endurance parameters, this relationship was almost linear while in the strength and power parameters the results were more in favour of a curvilinear relationship with limited benefit.

Influence of eccentric actions on skeletal muscle adaptations to resistance training

Three different training regimens were performed to study the influence of eccentric muscle actions on skeletal muscle adaptive responses to heavy resistance exercise. Middle-aged males performed the leg press and leg extension exercises two days each week. The resistance was selected to induce failure within six to twelve repetitions of each set. Group CON/ECC (n = 8) performed coupled concentric and eccentric actions while group CON (n = 8) used concentric actions only. They did four or five sets of each exercise. Group CON/CON (n = 10) performed twice as many sets with only concentric actions. Eight subjects did not train and served as controls. Tissue samples were obtained from m. vastus lateralis using the biopsy technique before and after 19 weeks of training, and after four weeks of detraining. Histochemical analyses were performed to assess fibre type composition, fibre area and capillarization. Training increased (P less than 0.05) Type IIA and decreased (P less than 0.05) Type IIB fibre percentage. Only group CON/ECC increased Type I area (14%, P less than 0.05). Type II area increased (P less than 0.05) 32 and 27%, respectively, in groups CON/ECC and CON/CON, but not in group CON. Mean fibre area increased (P less than 0.05) 25 and 20% in groups CON/ECC and CON/CON, respectively. Capillaries per fibre increased (P less than 0.05) equally for Type I and Type II fibres. Capillaries per fibre area for both fibre types, however, increased (P less than 0.05) only in groups CON and CON/CON. The changes in fibre type composition and capillary frequency were manifest after detraining.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of training on central factors in fatigue following two- and one-leg static exercise in man

Leg strength and fatigue developed during 150 repeated two- and one-leg isometric maximal voluntary contractions were determined before and after a 5-week one- (n = 6) or two- (n = 7) leg training programme including a control group of five subjects. Two- and one-leg training increased two- and one-leg strength by 59 (range 8-107) and 36% (-1-69) respectively (P less than 0.01) with no significant difference between the two groups. Two-leg training decreased (P less than 0.05) fatigue only during two-leg maximal voluntary contractions (from 20 [11-26] to 13% [6-27]); and one-leg training fatigue only during one-leg maximal voluntary contractions (from 20 [15-23] to 11% [9-24]) despite the fact that both legs were trained. Surface electromyographic activity decreased during both repeated two- and one-leg maximal voluntary contractions (P less than 0.01) but a reduction in electromyographic decay was seen (P less than 0.05) during two-leg maximal voluntary contractions after two-leg training. Training increased fast-twitch b fibre size (P less than 0.01), and glycogen depletion was seen in fast-twitch (a and b) fibres, but the relative fast-twitch b area did not increase significantly. No training effects were seen in the control group. The results show that an approximately 47% increase in muscle strength may take place without a significant change in the relative percentage of muscle fibre types or in the average muscle fibre size. Furthermore, the specificity of the training response to fatigue developed during repeated two- and one-leg maximal voluntary contractions suggests a change in the nervous influence on the motor units.

Velocity-specific and mode-specific effects of eccentric isokinetic training of the hamstrings

Ms. Ryan and Ms. Magidow completed this research project in partial fulfillment of the requirement for the degree of Masters of Science in the Department of Physical Therapy in the Graduate School, Duke University, 1989 This study examined velocity-specific and mode-specific effects of eccentric isokinetic training of the hamstrings. Female volunteers aged 21 to 40 were assigned to an exercise group (n = 17) or nonexercise group (n = 17). The average force of three concentric and eccentric hamstring contractions was evaluated pre- and post-training at 120 degrees /sec +/- 60 degrees /sec. Subjects trained three times a week for six weeks with 15 maximal eccentric isokinetic contractions at 120 degrees /sec. The ANOVA procedure and T-tests were used to determine the effects of training. A general linear model (GLM) for repeated measures determined the interaction effect between speed and mode. Results showed that the exercise group increased significantly (p < 0.0083) in eccentric force at all tested speeds and increased significantly (p < 0.0083) in concentric force at 120 degrees /sec and 180 degrees /sec. The GLM results showed no interaction effect between speed and mode. The study concluded that eccentric isokinetic training of the hamstrings at 120 degrees /sec is not speed-specific at 120 degrees /sec +/- 60 degrees /sec and is not mode-specific at 120 degrees /sec and 180 degrees /sec. J Orthop Sports Phys Ther 1991;13(1):33-39.

Effects of eccentric and concentric muscle actions in resistance training

The adaptive responses to two different resistance training regimens were compared. Healthy males performed five sets of either 12 maximum bilateral concentric (Grp CON; n = 11) or six pairs of maximum bilateral eccentric and concentric (Grp ECCON; n = 11) quadriceps muscle actions three times per week for 12 weeks. Uni- and bilateral eccentric and concentric peak torque at various angular velocities, vertical jump height and three-repetition maximum half-squat were measured before and after training. Muscle biopsies were obtained from m. vastus lateralis and analysed for fibre type composition and area using histochemical techniques. In contrast to a control group (n = 7), performing no training, Grps CON and ECCON demonstrated marked increases (P less than 0.05) in overall eccentric (19 and 37% respectively) and concentric (15 and 26% respectively) peak torques. Grp ECCON, however, showed greater (P less than 0.05) increases in peak torque, vertical jump height and three repetition maximum than Grp CON. The 7% increases in slow-twitch fibre area in Grps CON and ECCON and in fast-twitch fibre area in Grp CON were non-significant. This study suggests that increases in peak torque and strength-related performance parameters were greater following a programme consisting of maximum concentric and eccentric muscle actions than resistance training using concentric muscle actions only. Because increases in muscle fibre areas were small it is also suggested that the increased muscle strength shown subsequent to short-term accommodated resistance training is mainly due to neural adaptation.

Effect of high-intensity endurance training on isokinetic muscle power

The purpose of this study was to determine the effects of high-intensity endurance training on isokinetic muscle power. Six male students majoring in physical-education participated in high intensity endurance training on a cycle ergometer at 90% of maximal oxygen uptake (VO2max) for 7 weeks. The duration of the daily exercise session was set so that the energy expenditure equalled 42 kJ.kg-1 of lean body mass. Peak knee extension power was measured at six different speeds (30 degrees, 60 degrees, 120 degrees, 180 degrees, 240 degrees, and 300 degrees.s-1) with an isokinetic dynamometer. After training, VO2max increased significantly from mean values of 51.2 ml.kg-1.min-1, SD 6.5 to 56.3 ml.kg-1.min-1, SD 5.3 (P less than 0.05). Isokinetic peak power at the lower test speeds (30 degrees, 60 degrees and 120 degrees.s-1) increased significantly (P less than 0.05). However, no significant differences in muscle peak power were found at the faster velocities of 180 degrees, 240 degrees, and 300 degrees.s-1. The percentage improvement was dependent on the initial muscle peak power of each subject and the training stimulus (intensity of cycle ergometer exercise).

Eccentric and concentric torque-velocity relationships during arm flexion and extension. Influence of strength level

Forty men were tested with a computerized dynamometer for concentric and eccentric torques during arm flexion and extension at 0.52, 1.57, and 2.09 rad.s-1. Based on the summed concentric and eccentric torque scores, subjects were placed into a high strength (HS) or low strength (LS) group. The eccentric and concentric segments of the torque-velocity curves (TVCs) were generated using peak torque and constant-angle torque (CAT) at 1.57 and 2.36 rad. Angle of peak torque was also recorded. Compared to LS, HS had significantly greater estimated lean body mass (+10.2 kg) and approximately 25% greater average torque output. Reliability of the peak torque scores on 2 days in 20 subjects was r greater than or equal to 0.85. The difference between observed torques and the mathematically computed criterion torque scores averaged 1% for three validation loads that ranged from 11.4 to 90.4 kg. Statistical analysis revealed that torque output in LS plateaued at low concentric velocities and was also flattened with increasing eccentric velocities. Conversely, torque output for HS increased with decreasing concentric velocities and increased with increasing eccentric velocities. The method of plotting the TVCs for peak or CAT did not influence the pattern of TVC. Eccentric flexion peak torque occurred at a significantly shorter muscle length (1.88 rad) than concentric torque (2.12 rad). This difference was also present for extension; it was 1.88 rad for eccentric and 2.03 rad for concentric torque.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of velocity-specific strength training on peak torque and anaerobic rowing power

This study investigated the effect of low- and high-velocity resistance training on isokinetic peak torque and anaerobic power output. Eighteen male varsity oarsmen were blocked on peak knee extension torque at 3.14 rad s-1 and assigned to a high-velocity resistance training group (HVR), a low-velocity resistance training group (LVR) or a control group. Subjects trained four times a week for 5 weeks. Each training session included three circuits of 12 stations using variable-resistance hydraulic equipment. The HVR training significantly improved peak torque (P less than 0.05) in knee extension and flexion at 2.61, 3.14, 3.66 and 4.19 rad s-1. The LVR training produced significant improvements (P less than 0.05) in peak torque for knee extension and flexion at 0.52, 1.05, 1.57 and 2.61 rad s-1. High positive correlations were found between peak torque and anaerobic power outputs for all groups. However, no significant changes occurred in 15 s power output, average 90 s power output or peak blood lactate in either training group. These results indicate that velocity-specific strength training does not necessarily improve anaerobic power output in a different exercise mode despite the high positive correlation between isokinetic strength and anaerobic power output.

Maximal voluntary force of bilateral and unilateral leg extension

The aims were: (1) to investigate whether the 10-20% lower force during bilateral (BL) as compared to unilateral (UL) leg extension could be due to a general inability to activate fully a large number of muscles simultaneously, (2) to analyse the EMG signal of the quadriceps femoris during leg extensions, (3) to study the BL/UL force ratio in extension of the knee, and (4) to study the BL/UL leg extension force ratio in untrained and trained subjects. A 10% lower maximal voluntary isometric force was demonstrated during BL as compared to UL leg extension. This force discrepancy did not change when a total arm load of 250 N was applied simultaneously. Nor did the absolute force levels change, which indicates that the lower BL leg extension force is not due to a general mechanism of reduced activation with an increased number of muscles recruited in maximal voluntary contractions. Integrated EMG activity, mean power frequency and root mean square value of the EMG amplitude did not differ between UL and BL leg extensions. The knee extension force was slightly greater (4%) during BL than UL contractions. These findings are arguments against a reduced activation of the knee extensor muscles being the cause of the lower bilateral leg extension force. No differences in BL/UL force ratio were noted between groups of untrained and trained subjects despite the fact that several of the trained groups do different forms of BL leg extensions regularly. Thus, it does not appear that training readily affects the BL/UL leg extension force ratio.

Development of a computer system for real-time display and analysis of isokinetic data

An isokinetic analysis system was developed by interfacing an Akron isokinetic dynamometer to a microcomputer. The system was designed for real-time display of the muscular torque output in order to provide immediate visual feedback of the muscular performance. The muscular torque data were filtered for the effect of gravitational forces. The angular velocity of movement was monitored and only constant velocity data were used for analysis. Standard testing protocols for the assessment of muscle function in dynamic conditions have been implemented in the system.

Mode and speed specificity of eccentric and concentric exercise training

This research was supported by a Duke University Research Council Grant. The purpose of this study was to examine mode and speed specificity of strength training by comparing concentric and eccentric isokinetic exercise of the quadriceps. Forty-eight healthy men (mean age = 23.9 years) were randomly assigned to one of three groups: concentric training (C), eccentric training (E), or control (K). Average force (in Newtons) of 3 concentric and of 3 eccentric quadriceps contractions on the KIN-COM(R) dynamometer at 60, 120, and 180 degrees /sec was evaluated prior to and following a 6 week period during which only the C and E groups trained. Training sessions (3/week) included 4 submaximal and 1 maximal warm-up followed by 10 maximal effort isokinetic contractions of the quadriceps at 120 degrees /sec for each leg. Group C subjects trained concentrically only while Group E subjects trained eccentrically only. A t-test for independent means showed no significant right/left differences. ANOVA and Scheffe's F-tests were then used to assess the differences in training effects among the 3 groups for the left leg only. Results showed that although Group C increased slightly in both concentric and eccentric force at all speeds, the gains were significant only for concentric force at 180 degrees /sec. Group E showed significant gains (p < 0.05) in eccentric force at all speeds but not in concentric force. The K group had no significant change in concentric or eccentric force at any speed. We conclude that the eccentric mode of isokinetic exercise has highly specific strength training effects while the concentric mode has less specific training effects. In addition, speed of exercise does not appear to have specific training effects. J Orthop Sports Phys Ther 1989;11(2):70-75.

The influence of velocity-specific resistance training on the in vivo torque-velocity relationship and the cross-sectional area of quadriceps femoris

This work was supported by Sport Canada end Hydra-Fitness Industries. In order to investigate the effects of velocity-specific resistance training, 30 healthy, male varsity athletes were assigned to either high (HVR) or low (LVR) velocity training or control (CG) groups. Subjects completed two 20-sec sets of maximal exercise at each of six hydraulic resistance stations for the lower limb. Resistances were adjusted as necessary to maintain consistent average angular velocities of approximately 1.05 and 3.14 rad/sec for the LVR and HVR groups, respectively. Subjects trained on alternate days for 6 weeks, completing either two (weeks 1 and 2) or three (weeks 3-6) circuits of the six stations each session. Peak knee extension torques were improved (p < 0.05) for the LVR group at all of seven angular velocities tested between 1.05 and 4.19 rad/sec. Improvements (p < 0.05) were also observed for the HVR group, but only at angular velocities of 2.62, 3.14, 3.66, and 4.19 rad/sec. Cross-sectional area of the quadriceps femoris muscle group obtained from serial computer tomography (CT) scans was increased (p < 0.05) for both training groups. No significant changes in either strength or cross-sectional area were observed for control subjects. These results indicate that while both of the training programs resulted in increased cross-sectional area of the knee extensors, the observed changes in strength performance are likely due to other factors which may be mediated by the different training velocities. J Orthop Sports Phys Ther 1989;10(11):456-462.

Strength of two- and one-leg extension in man

Two- and one-leg extension strengths were compared in 155 female and male, untrained and trained (eight bicyclists, 38 weight-lifters) subjects and in a polio patient with almost no strength in one leg. On average two-leg strength was 82 +/- 1.3% (SE) of the sum of the strength of the right and left legs (leg-strength ratio) with no significant difference between the untrained and trained subjects. In the polio patient two-leg strength was lower than the strength of the strongest leg. A similar leg-strength ratio was found when measurements were made with a knee angle of 150 degrees (n = 128) and 90 degrees (n = 25). The ratio did not change when re-determined after 1 year (n = 9). Moderate changes in the subjects' position during measurements did not affect one-leg strength (n = 13). However, familiarization with the experimental apparatus increased the leg-strength ratio from 80 +/- 2.5% to 97 +/- 2.9% (P less than 0.01) (n = 18). In contrast, two-arm extension strength was similar to the sum of the strength of the right and left arms (n = 15). The results demonstrate that two-leg strength in general is lower than the sum of the strength of the right and left legs, and that this phenomenon is found even after intensive endurance or strength training. However, familiarization with the experimental apparatus can increase the relative two-leg strength which suggests that muscle strength in man may be limited by the central nervous systems' ability to activate maximally all synergistic muscles and/or to control antagonistic muscles.

The Influence of lsokinetic Muscle Torque Exerted in Various Speeds on Soccer Ball Velocity

Numerous variables influence soccer kick performance and among those initial soccer ball velocity is considered to be important. The purpose of this study was to investigate the correlation between initial ball velocity and two physical characteristics: relative isokinetic torque of the lower extremity and muscle contraction velocity. Eleven elite Greek soccer players age 25.5 +/- 3 years, weight 73.6 +/- 5.6 kg, height 176.5 +/- 5.5 cm, were tested on an isokinetic apparatus at different angular velocities to determine isokinetic muscle torque of the dominant lower extremity. To determine muscle contraction velocity and initial soccer ball velocity a cycling ergometer and a photocell apparatus were used, respectively. Relative isokinetic muscle torque values of the lower extremity were at 30 degrees /sec 3.29 +/- 0.32 Nm/kg, at 90 degrees /sec 2.49 +/- 0.28 Nm/kg, and at 180 degrees /sec 1.75 +/- 0.24 Nm/kg. Muscle contraction velocity was 3.69 +/- 0.27 c/s and initial ball velocity was 27.08 +/- 1.32 m/s. Initial ball velocity correlated significantly with relative isokinetic muscle torque at different angular velocities as follows: at 30 degrees /sec, r = 0.82, p < 0.01; at 90 degrees /sec, r = 0.73, p < 0.02; at 180 degrees /sec, r = 0.64, p < 0.05. Initial ball velocity was also significantly correlated with muscle contraction velocity (r = 0.77, p < 0.01). These results indicate that both physical qualities, i.e., relative isokinetic torque and muscle contraction velocity are significant variables related to soccer ball velocity which is considered to be an important factor of soccer kick performance.J Orthop Sports Phys Ther 1988;10(3):93-96.

Examining quadriceps/hamstrings performance at high velocity isokinetics in untrained subjects

The purpose of this study was to examine isokinetic torque production for untrained individuals at high isokinetic speeds. Data was collected at 300, 330, 360, 400, and 450 degrees /sec in the following areas: 1) Peak torque produced by the quadriceps and hamstrings;2) Percent torque/body weight;3) Quadriceps/hamstrings ratio; and4) Dominant versus nondominant lower extremities.Twenty-three men and 32 women aged 19-37 years ( or males = 27.4, for females = 27.6) were tested on the Biodex 8-2000 (Biodex Corporation, Shirley, NY). The peak torque (ft-lbs) ranges were: male quadriceps 68.9-76.8, male hamstrings 56.0-67.9, female quadriceps 33.8-36.5, female hamstrings 36.9-38.8. The percent torque/body weight ratio ranges were: male quadriceps 38.2-44.5%, male hamstrings 34.4-37.6%, female quadriceps 25.7-28.5% female hamstrings 28.6-30.0%. The quadriceps/hamstrings ratio ranges were: males 102.9-137.1%, females 92.4-98.9%. Significant differences (p > 0.05) were found between the hamstrings at 330, 360, and 400 degrees /sec in males and 300, 330, and 400 degrees /sec in females. The values presented in this study may be beneficial in defining deficits and rehabilitation goals in untrained individuals.J Orthop Sports Phys Ther 1988;10(1):18-22.

Impact of physical training on the ultrastructure of midthigh muscle in normal subjects and in patients treated with glucocorticoids

Exercise-training might be a logical method to reverse muscle atrophy and weakness in patients treated with glucocorticoids. The purpose of the present investigation was to establish whether a treatment with low dose prednisone (10 +/- 2.9 mg/d) modulates the effect of a moderate strength type isokinetic training during 7 wk (21 sessions of 20 min) on "muscle efficiency" (power output/muscle mass) and on concomitant changes in ultrastructure of the thigh muscle measured by quantitative electron-microscopic morphometry. Training caused a similar increase in "muscle efficiency" in patients on prednisone (n = 9) as in normal volunteers (n = 9). In normal subjects the increase in muscle efficiency was associated with an increase in sarcoplasm, whereas in patients on prednisone the functional improvement was associated with an increase in sarcoplasm, capillaries, and mitochondria content. Thus, a therapy with low dose prednisone does not abrogate training-induced improvement of muscle efficiency but modulates the ultrastructural response of the muscle to the training.

Slow or Fast lsokinetic Training after - Knee Ligament Surgery*

In order to evaluate the importance of training speed and training dose and its effect on muscle morphology, 16 patients operated on for an anterior cruciate ligament injury were randomly divided into two groups for isokinetic training. One group trained with slow speed (60 O/sec), 10 x 10 repetitions and one group with fast speed (180 O/sec), 10 x 15 repetitions. The effect of 8 weeks training three times per week was evaluated with Cybex I/@st rength tests, muscle biopsies, and computed tomography of the thigh muscles. No significant differences between the two groups were noted although the fast speed training group showed tendencies to increase in strength more at higher speeds than did the slow speed training group. Within the fast speed training group the increases at higher speeds were significantly larger than at slower speeds. There was also a tendency toward a larger increase of the cross-sectional area of the fast twitch fibers in the fast speed training group. There was no significant difference in the increase of the cross-sectional area of the quadriceps muscles between the two groups. The large dose of training did not yield larger increases in strength compared to one of our earlier studies that used 3 x 10 repetitions. J Orthop Sports Phys Ther 1987;8(10):475-479.

Strength-velocity relationship and fatiguability of unilateral versus bilateral arm extension

Strength-velocity relations and fatigue resistance in an arm bench press manoeuvre were compared between conditions of bilateral (BL, both arms acting together) and unilateral muscle contraction in 9 young men. BL and UL (sum of the 2 arms acting singly) strength was similar for isometric and slow isokinetic maximal voluntary contractions (MVC); at high velocities BL MVC declined more than UL. In both types of contractions a curvilinear relation was observed between strength and velocity, with significantly higher peak torques (PT) being produced under isometric conditions than for slow velocity efforts (p less than 0.01). Mean declines in PT during 100 repetitive MVCs of approximately 70s were to 25% of initial values for the BL fatigue test and to 37% for UL (p less than 0.01). In contrast to results of a similar investigation of leg extension in the same subjects, the arms showed no BL deficit of strength in the initial part of the strength-velocity curve and approximately twice as much fatigue in repetitive contractions. These physiological differences may stem from the varying habitual activity patterns of the arms and legs.

The effectiveness of a mini-cycle on velocity-specific strength acquisition

In order to investigate the rate of strength acquisition from high-velocity resistance (HVR) training, 21 college-aged males were assigned to either HVR training (N = 11) or a control group (N = 10). Subjects trained 4 days weekly over 5 weeks, completing two 20-second sets of all-out exercise separated by 20 seconds of rest at each of three variable hydraulic resistance stations. Initially, subjects completed two circuits, and progressed to three circuits during the third week. Angular velocities of movement were maintained at approximately 3.14 radianslsecond. Increases (p < 0.05) in peak torque during knee extension and flexion, and average peak torque over two 20-second sets of continuous knee extension and flexion exercise at 3.14 radianslsecond were observed after 10 training sessions. After 10 additional training sessions, no further significant increases in performance were observed. These data suggest that velocity-specific strength training .effects may be obtained with relatively small volumes of high-intensity resistance exercise. J Orthop Sports Phys Ther1987;9(4):156-159.

An analysis of hamstring strains and their rehabilitation

The recurrent hamstring strain is a problem that is dealt with at all levels of athletics. The complex action of the hamstrings, as evident by EMG data, as well as a poor understanding of the mechanism of injury, are possible reasons for this high rate of reinjury. Another possible cause deals with the rehabilitation protocol utilized in treating this injury. Early controlled motion and specific exercises designed to apply to the unique characteristics of the hamstring muscles are necessary to completely rehabilitate the athlete and successfully prevent a recurrence. This program must include a progressive resumption of activity with an emphasis on high speed movements. A model hamstring rehabilitation program is proposed. J Orthop Sports Phys Ther 1987;9(2):77-85.

Muscular power in young women after slow and fast isokinetic training*

The purpose of this study was to determine, via a pilot study, if training at a fast isokinetic velocity (180 degrees /sec) would result in a greater increase in upper-extremity muscular power than training at a slow isokinetic velocity (60 /sec) while exercising through a specific range of motion (1 80"). Twenty normal young women were randomly selected into one high velocity and one slow velocity experimental group. The exercise protocol consisted of four bouts of five maximal reciprocal isokinetic contractions of the shoulder flexor and extensor muscle groups, three times a week for four weeks. Pre- and post-testing with a Cybex I$ isokinetic dynamometer was performed to determine if significant power gains were elicited within the training range of motion. Aiter training, both fast and slow velocity groups showed significant power gains (p < 0.0005). However, the results indicated that neither fast nor slow isokinetic training is more effective for power production within the 1 80 degrees range of motion of shoulder extension in the young women studied. J Orthop Sports Phys Ther 1986;8(1);1-9.

Training-induced changes in neuromuscular performance under voluntary and reflex conditions

To investigate training-induced changes in neuromuscular performance under voluntary and reflex contractions, 11 male subjects went through heavy resistance (high loads of 70-120% of one maximum repetition) and 10 male subjects through explosive type (low loads with high contraction velocities) strength training three times a week for 24 weeks. A large increase (13.9%, p less than 0.01) in voluntary unilateral maximal knee extension strength with only slight and insignificant changes in time of isometric force production were observed during heavy resistance strength training. Explosive type strength training resulted in a small insignificant increase in maximal strength but in considerable shortening (p less than 0.05) in the time of force production. A significant increase (p less than 0.05) noted in the averaged maximal integrated electromyogram (IEMG) of the knee extensors during heavy resistance strength training correlated (p less than 0.01) with the increase in maximal strength. No changes were noted during training in reflex time components, but significant decreases (p less than 0.05) occurred in the peak-to-peak amplitudes of the reflex electromyograms (EMG) in both groups. The individual changes during training in the reflex EMG/force ratio were related (p less than 0.01) to the respective changes in IEMG/force ratio in voluntary contractions. The present observations support the concept of specificity of training, and suggest that specific training-induced adaptations in the neuromuscular system may be responsible for these changes in performance.

Speed-Specific lsokinetic Training

The authors studied the effects of high speed (240 degrees /sec) and low speed (60 degrees /sec) isokinetic exercise. Twenty-four subjects were randomly selected into one high speed and one low speed treatment group; treatments consisted of one set of 15 repetitions, 3 times a week for 6 weeks. Pre- and post-testing with a Cybex II isokinetic dynamometer was performed to determine if significant strength gains were elicited at 30, 60, 180, 240, or 300 degrees /sec. Both low and high speed groups produced significant strength gains (0.0 1 significance level) at their treatment speed and at one testing speed higher. However, this study indicates that the range of this carry over is not sufficient enough to replace speed-specific training. J Orthop Sports Phys Ther 1984;6(3):181-183.

Specificity of velocity in strength training

Twenty-one male volunteers (ages 23-25 years) were tested pre- and post training for maximal knee extension power at five specific speeds (1.05, 2.09, 3.14, 4.19, and 5.24 rad X s-1) with an isokinetic dynamometer. Subjects were assigned randomly to one of three experimental groups; group S, training at 1.05 rad X s-1 (n = 8), group I, training at 3.14 rad X s-1 (n = 8) or group F, training at 5.24 rad X s-1 (n = 5). Subjects trained the knee extensors by performing 10 maximal voluntary efforts in group S, 30 in group I and 50 in group F six times a week for 8 weeks. Though group S showed significant increases in power at all test speeds, the percent increment decreased with test speed from 24.8% at 1.05 rad X s-1 to 8.6% at 5.24 rad X s-1. Group I showed almost similar increment in power (18.5-22.4 at all test speeds except at 2.09 rad X s-1 (15.4%). On the other hand, group F enhanced power only at faster test speeds (23.9% at 4.19 rad X s-1 and 22.8% at 5.24 rad X s-1).

Relationship between isokinetic performance and ballistic movement

The present experiments were carried out to assess the relationship between the mechanical behaviour of the leg extensor muscles in 12 male athletes during activities of a ballistic type and torque production, during: (1) torque production during isokinetic contraction: (2) ballistic type activities (vertical jumps from statis position = SJ, with counter-movement equal CMJ and after a fall from different heights equal DJ) and (3) a new anaerobic test (Bosco 1983a). This consisted of performing continuous jump work for a certain period of time (e.g., 60 s). Both ballistic activities and anaerobic power tests demonstrated the highest relationship with peak torques when this was developed respectively at pi and 4.2 rad x s-1. Peak torque was related to SJ (r = 0.71, p less than 0.01); to CMJ (r = 0.74, p less than 0.005); to best DJ (r = 0.60, p less than 0.05), to 15 s anaerobic power (r = 0.70, p less than 0.01) and 60 s anaerobic power (r = 0.68, p less than 0.01). The power output during ballistic activities was much higher than the power measured during zero acceleration performances. The difference noted was explained in the light of the fact that, when jumping, three different extensor muscle groups in each leg contract with re-use during the concentric phase of elastic energy stored during the eccentric phase. The relationship between isokinetic contraction and ballistic motion is discussed in terms of fiber type recruitment and their velocity dependency.

Effect of isometric and isokinetic muscle training on static strength and dynamic power

This study investigated whether isokinetic strength training might induce changes in static and dynamic power already achieved as a result of isometric strength training. The subjects were twelve males. The isometric strength and dynamic power of elbow flexors were tested by means of an electric dynamometer and fly-wheel every two weeks. During the first 8 weeks all subjects trained the elbow flexors isometrically at four different positions of elbow joints. This training produced 27-36% gains in isometric strength and 34-46% in power. Thereafter the subjects were divided into two groups: the FG group who trained isokinetically at a fast velocity of 157 degrees . s-1, and the SG group at slow velocity of 73 degrees . s-1. After 6 weeks of training, the FG group produced a significant gain in power with light equivalent masses and the SG group did so with heavy equivalent masses. Neither group showed change in isometric strength.

Muscle performance, morphology and metabolic capacity during strength training and detraining: a one leg model

To investigate biochemical, histochemical and contractile properties associated with strength training and detraining, six adult males were studied during and after 10 weeks of dynamic strength training for the quadriceps muscle group of one leg, as well as during and after a subsequent 12 weeks of detraining. Peak torque outputs at the velocities tested (0-270 degrees X s-1) were increased (p less than 0.05) by 39-60% and 12-37% after training for the trained and untrained legs, respectively. No significant changes in peak torques were observed in six control subjects tested at the same times. Significant decreases in strength performance of the trained leg (16-21%) and untrained leg (10-15%) were observed only after 12 weeks of detraining. Training resulted in an increase (p less than 0.05) in the area of FTa (21%) and FTb (18%) fibres, while detraining was associated with a 12% decrease in FTb fibre cross-sectional area. However, fibre area changes were only noted in the trained leg. Neither training nor detaining had any significant effect on the specific activity of magnesium-activated myofibrillar ATPase or on the activities of enzymes of phosphagen, glycolytic or oxidative metabolism in serial muscle biopsy samples from both legs. In the absence of any changes in muscle enzyme activities and with only modest changes in FT fibre areas in the trained leg, the significant alterations in peak torque outputs with both legs suggest that neural adaptations play a prominent role in strength performance with training and detraining.

Isokinetic rehabilitation after surgery. A review of factors which are important for developing physiotherapeutic techniques after knee surgery

The postoperative rehabilitation of individuals who've had surgery has been a primary concern of all members of the health care community. With the advent of new training devices for use during the rehabilitation period (i.e., isokinetic training devices) and new research in sports medicine, there has been a renewed interest in how to best rehabilitate individuals following surgery (knee surgery, in particular). This paper briefly reviews basic muscle physiology as it relates to muscle fiber types and recruitment patterns. Subsequently, it reviews studies that have investigated muscle atrophy and methods to reduce muscle dysfunction related to surgery, immobilization, and disuse. Finally, it reviews isokinetic training studies and examines the concept of "specificity of speed" training. These principles of muscle physiology and muscle plasticity are then applied to a proposed isokinetic rehabilitation program which might be adapted for use following joint surgery.