Walter Kroll

Practice Effects on Fractionated Response Time Related to Age and Activity Level

Two days of practice on simple and choice reaction (RT) and movement time (MT) were studied using 60 males placed into four groups based upon age and physical activity level. Practice effects upon simple and choice RTs were different for young and old groups. Only the two inactive groups improved on simple and choice MT, with greatest improvement occurring on simple MT. Old Actives had true-score variance than the Old Inactives, but much greater than the two young groups. Intraindividual variability was greater for the two older groups even in the absence of practice effects. Results support the claim that a life style or regular physical activity may lessen aging effects upon RT and MT as well as attenuating interindividual variability.

Rapid Movement Kinematic and Electromyographic Control Characteristics in Males and Females

Maximally fast, self-terminated elbow flexion movements were performed by 10 male and 10 female college-aged subjects to assess potential gender-related differences in kinematics and the triphasic electromyographic (EMG) pattern. The subjects were instructed to move their forearms as fast as possible through 90 degrees of elbow flexion range of motion and stop as sharply as possible at the terminal point. An electromagnet, set to 0, 40, and 70% of each subjects maximal isometric torque, provided resistance to movement initiation and resulted in quick release movements. Surface EMG was collected from the biceps b. and triceps b. muscles. Results indicated that the males had faster movements and accelerations under all conditions. EMG records indicated that the males had faster rates of EMG rise, particularly in the triceps b., and more tightly coupled reciprocal activation. The quick release afforded faster accelerations for both groups, yet only the males moved faster throughout the full range of motion. Following the quick release, the males differed from the females by increasing the triceps b. EMG amplitude. Hence, the males were able to shorten movement time in quick release movements by increasing triceps b. activation and, thus, braking ability. These results suggest that the females were more neurally constrained than the males with respect to rapid EMG activation of the triceps b., resulting in limits in the braking process.

Maximal isometric strength and fiber type composition in power and endurance athletes

SummaryThe relationship between maximum isometric strength and muscle fiber type composition was examined in seven endurance and eight power trained athletes. Knee extension strength and ankle extension strength was assessed on 10 separate days and muscle biopsies were taken from the vastus lateralis and gastrocnemius muscles. The percent composition of slow twitch (ST) fibers and fast twitch (FT) fibers was determined from the biopsy samples. Correlation between maximal knee extension strength and percent ST fibers of the vastus lateralis was found to be 0.80 (n=8, p<0.05) for the power group and 0.63 (n=7, N.S.) for the endurance group. Corresponding correlation coefficients for the relationship between ankle extension strength and gastrocnemius percent ST fibers were −0.94 (p<0.01) and −0.19 (N.S.), respectively. The results suggest that the relationship to be expected between muscle fiber type composition and maximum isometric strength may well depend upon the muscle group under study as well as the type of athlete in terms of specific training adaptations.

Isokinetic strength, endurance, and fiber type composition in elite American paddlers

SummaryMuscle fiber type and isokinetic strength and fatigue were examined in nine highly trained canoe and kayak paddlers. Needle biopsies were taken from the right vastus lateralis and biceps brachii muscles and the samples stained for myofibrillar ATPase. Baseline elbow flexion and knee extension isometric (0‡·s−1) and isokinetic (60‡·s−1 or 1.05 rad·s−1 and 180‡·s−1 or 3.14 rad·s−1) peak torques were determined. Each subject then performed two series of 50 isokinetic contractions at an angular velocity of 180‡·s−1: elbow flexion and knee extension series, separated by 3 h. The percentage of slow twitch fibers was similar in the biceps brachii (43.9%) and the vastus lateralis (43.3%). The fast twitch/slow twitch fiber area ratio was significantly higher in the more highly trained biceps brachii due to larger FT fibers. No relationship was found between fiber type composition and baseline peak torques or decline in peak torque due to the fatigue regimens. Baseline peak torque correlated with initial strength level, body weight, and limb girth. The results suggested that for these paddlers muscle strength and the decline in strength induced by repetitive isokinetic contractions were more dependent on characteristics of body size than on fiber type composition.

Effects of local muscular fatigue due to isotonic and isometric exercise upon fractionated reaction time components.

Fractionated RT for a right knee-extension task was assessed on eight male and eight female Ss over eight treatment days. Following four consecutive days of 75 RT trials /day to insure stabilized strength and RT components, Ss were administered two days of bench stepping and two days of isometric exercise designed to induce muscular fatigue of the knee extensors. Significant strength decrements of up to 24% were induced by both the isotonic (bench stepping) and isometric exercise treatment conditions but no changes were observed in fractionated RT components. The results would seem to indicate that performance differences in fine-versus gross-motor skill tasks due to fatigue need to be more carefully examined.

Muscle Fiber Type Composition and Knee Extension Isometric Strength Fatigue Patterns in Power- and Endurance-Trained Males

Abstract Muscle fiber type composition in the vastus lateralis and knee extension isometric strength fatigue patterns were assessed in eight endurance-trained and eight power-trained males. Two different 25-trial isometric contraction exercise regimens were administered: a 10-second contraction, 5-second intertrial rest condition designed to induce a fast rate of fatigue and a 10-second contraction, 20-second intertrial rest condition designed to induce a slower rate of fatigue. The power group fatigued almost four times faster than the endurance group in the 10:5 exercise condition. In the 10:20 exercise condition, the endurance group showed no fatigue pattern while the power group had a significant strength decrement of 32%. In both exercise conditions, the power group exhibited more complex fatigue patterns in terms of statistically significant trend components. Maximum isometric strength correlated positively with slow twitch (ST) percent number in power (r = .80) and endurance (r = .48) groups, but n...

Plantar flexion fatigue and muscle fiber type in power and endurance athletes.

Plantar flexion fatigue and muscle fiber type in power and endurance athletes. Med. Sci. Sports Exercise, Vol. 12, No. 4, pp. 262-267, 1980. The relationship between isometric plantar flexion strength fatigue patterns and muscle fiber type composition of the gastrocnemius was assessed in endurance (N = 8) and power (N = 8) trained males. Following baseline strength assessment, subjects were administered two different 25 trial isometric exercise regimens: on one exercise day each 10-sec fatigue trial was separated by a five-sec intertrial rest period, while on the second exercise day the 10-sec fatigue trials was separated by a 20-sec intertrial rest periods. Muscle biopsies were secured from the right medial gastrocnemius. Significantly different fatigue patterns resulted between power and endurance groups, with the power group fatiguing five times faster than the endurance group in the 10.5 condition and demonstrating more complex fatigue curves in both exercise conditions. Slow twitch fiber percent number correlated with rate of fatigability as measured by linear trend coefficients in power (r = .84) and endurance groups (r = .26). Rate of fatigability correlated with maximum isometric strength in both power (r = -.66) and endurance (r = .86) groups. Thus, maximum isometric strength was a better predictor of rate of fatigability than muscle fiber type composition.

Exercise effects upon reflex time components in weight lifters and distance runners

In an effort to identify neuromuscular parameters which differentiate between power-type and endurance-type athletes, an investigation was conducted to determine the effects of an isometric exercise task upon patellar and Achilles fractionated reflex time components in a group of weight lifters and long-distance runners. A reflex hammer was used to deliver a tendon tap stimulus to the patellar tendon (sitting position) and the Achilles tendon (prone position). Under resting conditions, no differences in Achilles reflex components existed between the two subject groups. However, patellar reflex latency was significantly shorter in the weight lifters than in the distance runners. Following knee extensor exercise consisting of three bouts of a 50% MVC holding-time task, the power group manifested a marked lengthening in total reflex time and reflex motor time. In the endurance group, reflex time lengthened after the first bout, but became shorter after the last two bouts. A similar Achilles reflex pattern was seen in both groups after plantar flexor exercise--an initial elongation of the peripheral components of reflex time, followed by a trend towards shorter reflex components in the later bouts. It was suggested that several factors may be competing to produce the bi-directional results observed in reflex time components following isometric exercise.

Fractioned Reaction Ttme in Power-Trained and Endurance-Trained Athletes under Conditions of Fatiguing Isometric Exercise

Fractionated knee extensor and plantar flexor reaction time (RT) components were assessed in a group of eight weightlifters and eight long distance runners. Following a 4-day period of baseline stabilization for each muscle group, a 50% maximal voluntary contraction (MVC) holding-time exercise was administered. Results showed that the runners had longer premotor times (PMT) than the weightlifters in the knee extensors, but had much faster PMTs than the lifters in the plantar flexor condition. Compared to previously reported investigations using non-athletes, the data for the present sample of athletes indicated faster total reaction times(TRT) in both the knee extensors and the plantar flexors. A resistance of 15% MVC applied during the RT task resulted in a lengthening of the motor time (MT) component in both groups prior to exercise. However, while knee extensor resisted motor time was lengthened by the exercise task, no such lengthening occurred in plantar flexor resisted RT. It is concluded that power-trained and endurance-trained athletes exhibit difference in response to a fractionated RT task, under both baseline and fatiguing exercise conditions.

Test Reliability and Errors of Measurement at Several Levels of Absolute Isometric Strength.

Abstract Five maximal isometric wrist flexion strength trials of 5-sec. duration and spaced 1-min. apart were secured on two separate days one week apart. Intraclass correlation techniques were used to partition error variance and true score variance estimates on 75 college females classified into high, middle, and low levels of absolute strength groups; 30 male subjects were also included. Data were analyzed for left and right wrists for the female subjects and for the right wrist of males. The low strength females demonstrated the smallest error variance estimates for trials and days on both wrists. Middle and high strength females exhibited error variance estimates two to three times larger than the low strength females. Right wrist data on male subjects showed the largest error variance, with trials and day error variances some two to four times larger than the female subjects. Since error variance seems to be related to the magnitude of the strength score, further caution is indicated in the interpre...