The validity, reliability, and protocol for the interpolated twitch technique (ITT) were investigated with isometric plantar flexor and leg extension contractions. Estimates of muscle inactivation were attempted by comparing a variety of superimposed with potentiated evoked torques with submaximal and maximal voluntary contraction (MVC) torques or forces. The use of nerve and surface stimulation to elicit ITT was reliable, except for problems in maintaining maximal stimulation with nerve stimulation at 20 degrees plantar flexion and during leg extension. The interpolated twitch ratio-force relationship was best described by a shallow hyperbolic curve resulting in insignificant MVC prediction errors with second-order polynomials (1.1-6.9%). The prediction error under 40% MVC was approximately double that over 60% MVC, contributing to poor estimations of MVC in non-weight-bearing postimmobilized ankle fracture patients. There was no significant difference in the ITT sensitivity when twitches, doublets, or quintuplets were used. The ITT was valid and reliable when high-intensity contractions were analyzed with a second-order polynomial.

The effects of fatigue duration and muscle type on voluntary and evoked contractile properties were investigated with an isometric, intermittent, submaximal fatigue protocol. Four groups performed contractions of the plantar flexors and quadriceps at various intensities to produce long (LDF; 19 min 30 s)- and short-duration fatigue (SDF; 4 min 17 s). The LDF group had a significantly greater decrease in muscle activation than did the SDF group (12 vs. 5.8%) during recovery, although there was no difference in the impairment of maximum voluntary contraction force beyond 30 s of recovery. The significant decrease in the compound muscle action potential of the LDF group (M-wave amplitude; 14.7%) contrasted with the M-wave potentiation of the SDF group (15.7%), suggesting changes in membrane excitation may affect LDF. The quadriceps group performing contractions at 50% MVC experienced a smaller decrease in agonist electromyograph activity than did other groups, indicating both muscle and fatigue duration specificity. Impairments in excitation-contraction coupling were indicated by changes in quadriceps peak twitch and time to peak twitch while decreases in PF M-wave amplitudes suggested a disruption of membrane potentials. Results suggest that fatigue mechanisms may be duration (activation, half relaxation time) or muscle specific (electromyograph, twitch torque) or a combination of both (M wave, time to peak twitch torque).

Twenty male and 20 female non-professional tennis players were classified into two different age groups (n = 10 per group): young active men (30.4 +/- 3.3 years), young active women (27.5 +/- 4.3 years), elderly active men (64.4 +/- 3.7 years), and elderly active women (65.3 +/- 4.5 years). These individuals were matched (n = 10 per group) according to sex, age, height and mass to sedentary individuals of the same socio-economical background: young sedentary men (29.2 +/- 3.4 years), young sedentary women (25.6 +/- 4.4 years), elderly sedentary men (65.2 +/- 3.2 years) and elderly sedentary women (65.6 +/- 4.4 years). An isokinetic dynamometer was used to measure the strength of the knee extensors and flexors (two separate occasions) and the endurance of the extensors. Vastus lateralis electromyogram (EMG) was measured concomitantly. Significant sex, age and exercise effects (P less than 0.001) were observed for peak torque of both muscle groups. The effect of age on extensor strength was more pronounced at high speeds where men were also able to generate larger relative torques than women. No age or sex effects were noted for muscle endurance. However, muscles of active individuals demonstrated a greater resistance to fatigue than those of sedentary individuals. In conclusion, men were found to be stronger than women, age was associated with a decrease in muscle strength, but not of muscle endurance, and tennis players were stronger and had muscles that were more resistant to fatigue than their sedentary pairs in both age groups.(ABSTRACT TRUNCATED AT 250 WORDS)

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t has been shown in animals that fast-twitch skeletal muscles are able to recover fullv from the nefarious effects of joint immobilization without benefit of cxercise training (14.59). It has also been demonstrated that exercise training can accelerate the recovery of various muscle properties from a period of disuse (1 5.28.54). In humans, the acceleration of muscle size and strength recovery through exercise training has been assumed but never conclr~sivelv proven. Indeed, since a control group of sr~hjects allowed to recover spontaneor~sly ( n o supervised exercise training) has not been inclr~detl in the design of most p r e v i o~~s studies (3.1 5.1 g,'L.?.52), it is not known to what extent human skeletal muscles can recover after a period of disuse without supplementing normal daily activity with supervised exercise training.In an earlier study (53), we investigated the effects of isokinetic strength training on the recovery of mr~scle torques in the extensors and flexors of the knee. Subjects were randomlv assigned to an experimental group that started training at 2 weeks postoperation for 4 weeks (three times weekly). In contrast, the control group did not receive supervised training during this period. M' e were unable to demonstrate that isokinetic training was beneficial in the recovery of rnr~scle strength following this type of surgery, as both the trained and untrained groups had recovered to their preoperative values by 6 weeks postsurgery. From 6-10 (60, 120, 180, and 240°/sec) (involved and uninvolved, speed (60, 120, 180, and 240°/sec), or time (preoperative, 2, 4, 6, 8, 10, and 12 weeks, the previouslv untrained group commenced training while the experimental group continued training. Strength gains varying between 10 and 16% (depending on the velocity) were ohsenred in both groups. However, as all sr~bjccts were being trained, it was not possible to determine to what extent supenised training o r spontaneous recovery contrih uted to this improvement. More information o n the time course of spontaneous recovery fidlowing arthroscopic parti;d meniscectomy was necessary in order to plan a clinical trial to determine whether training can accelerate the recovery of muscle function following this type of surgery. Indeed, sample size determination requires knowledge of the clinical difference expected behveen no training and training groups as well as information on the variability of the patient population. Therefore, the purpose ol' this study was to investigate the time course of spontaneous recovery ( n o supervised training) of muscle torques in the first 3 months postarthroscopic partial meniscectom?. A comparison of the current R E S E A R C H S T U D Yresults with those of the previous study where subjects trained until 10 weeks postsurgen \vordd allow a reasonable estimate of sample size for a clinical trial. As the extent of recove n may be influenced by the degree to which subjects exercise on their own, their activity level was closely monitored. METHODS SubjectsTwentytwo subjec...