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At least 235 records · Page 13Linked to original sources
PubMed2005

Effects on the crank torque profile when changing pedalling cadence in level ground and uphill road cycling.

Despite the importance of uphill cycling performance during cycling competitions, there is very little research investigating uphill cycling, particularly concerning field studies. The lack of research is partly due to the difficulties in obtaining data in the field. The aim of this study was to analyse the crank torque in road cycling on level and uphill using different pedalling cadences in the seated position. Seven male cyclists performed four tests in the seated position (1) on level ground at 80 and 100 rpm, and (2) on uphill road cycling (9.25% grade) at 60 and 80 rpm.The cyclists exercised for 1 min at their maximal aerobic power. The bicycle was equipped with the SRM Training System (Schoberer, Germany) for the measurement of power output (W), torque (Nm), pedalling cadence (rpm), and cycling velocity (km h(-1)). The most important finding of this study indicated that at maximal aerobic power the crank torque profile (relationship between torque and crank angle) varied substantially according to the pedalling cadence and with a minor effect according to the terrain. At the same power output and pedalling cadence (80 rpm) the torque at a 45 degrees crank angle tended (p < 0.06) to be higher (+26%) during uphill cycling compared to level cycling. During uphill cycling at 60 rpm the peak torque was increased by 42% compared with level ground cycling at 100 rpm. When the pedalling cadence was modified, most of the variations in the crank torque profile were localised in the power output sector (45 degrees to 135 degrees).

Adaptation, Physiological↗
PubMed2003

Joint torques during sit-to-stand in healthy subjects and people with Parkinson's disease.

OBJECTIVES: To compare lower limb joint torques during sit-to-stand in normal elderly subjects and people with Parkinson's disease, using a developed biomechanical model simulating all phases of sit-to-stand.Design. A cross-sectional study utilizing a Parkinsonian and a control group. BACKGROUND: Subjects with Parkinson's disease were observed to experience difficulty in performing sit-to-stand. The developed model was used to calculate the lower limb joint torques in normal elderly subjects and subjects with Parkinson's disease, to delineate possible causes underlying difficulties in initiating sit-to-stand task. METHODS: Six normal elderly subjects and seven age-matched subjects with Parkinson's disease performed five sit-to-stand trials at their self-selected speed. Anthropometric data, two-dimensional kinematic and foot-ground and thigh-chair reactive forces were used to calculate, via inverse dynamics, the joint torques during sit-to-stand in both before and after seat-off phases. The difference between the control and Parkinson's disease group was analysed using independent t-tests. RESULTS: Both control and Parkinson's disease groups had a similar joint kinematic pattern, although the Parkinson's disease group demonstrated a slower angular displacement. The latter subjects produced significantly smaller normalized hip flexion torque and presented a slower torque build-up rate than the able-bodied subjects (P<0.05). CONCLUSION: Slowness of sit-to-stand in people with Parkinson's disease could be due to a reduced hip flexion joint torque and a prolonged rate of torque production.

Ankle Joint↗
PubMed2003

Reliability of electromyographic and torque measures during isometric axial rotation exertions of the trunk.

OBJECTIVE: The aim of the present study was to investigate the between-days reliability of electromyographic (EMG) measurement of 6 bilateral trunk muscles and also the torque output in 3 planes during isometric right and left axial rotation at different exertion levels. METHODS: Ten healthy subjects performed isometric right and left axial rotation at 100, 70, 50 and 30% maximum voluntary contractions in two testing sessions at least 7 days apart. EMG amplitude and frequency analyses of the recorded surface EMG signals were performed for rectus abdominis, external oblique, internal oblique, latissimus dorsi, iliocostalis lumborum and multifidus bilaterally. The primary torque in the transverse plane and the coupling torques in sagittal and coronal planes were measured. RESULTS: For both EMG amplitude and frequency values, good (intraclass correlation coefficient, ICC=0.75-0.89) to excellent (ICC>/=0.90) reliability was found in the 6 trunk muscles at different exertion levels during axial rotation. The reliability of both maximal isometric axial rotation torque and coupling torques in sagittal and coronal planes were found to be excellent (ICC>/=0.93). CONCLUSIONS: Good to excellent reliability of EMG measures of trunk muscles and torque measurements during isometric axial rotation was demonstrated. This provides further confidence of using EMG and triaxial torque assessment as outcome measures in rehabilitation and in the evaluation of the human performance in the work place.

Abdominal Muscles↗
PubMed1997

Osseointegration enhanced by chemical etching of the titanium surface. A torque removal study in the rabbit.

Roughened implant surfaces are thought to enhance osseointegration. Torque removal forces have been used as a biomechanical measure of anchorage or osseointegration in which the greater forces required to remove implants may be interpreted as an increase in the strength of osseointegration. The purpose of this study was to compare the torque resistance to removal of screw shaped titanium implants having an acid etched (HC1/H2SO4) surface (Osseotite) with implants having a machined surface. Two custom screw shaped implants, 1 acid etched and the other machined, were placed into the distal femurs of 10 adult New Zealand White rabbits. These implants were 3.25 mm in diameter x 4.00 mm in length without holes, grooves or slots to resist rotation. Following a 2 month healing period, the implants were removed under reverse torque rotation with a digital torque measuring device. Two implants with the machined surface preparation failed to achieve osseointegration. All other implants were found to be anchored to bone. Resistance to torque removal was found to be 4 x greater for the implants with the acid etched surface as compared to the implants with the machined surface. The mean torque values were 20.50 +/- 6.59 N cm and 4.95 +/- 1.61 N cm for the acid etched and machined surfaces respectively. The results of this study suggest that chemical etching of the titanium implant surface significantly increases the strength of osseointegration as determined by resistance to reverse torque rotation.

Acid Etching, Dental↗
PubMed2001

Early endosseous integration enhanced by dual acid etching of titanium: a torque removal study in the rabbit.

Textured implant surfaces are thought to enhance endosseous integration. Torque removal forces have been used as a biomechanical measure of anchorage, or endosseous integration, in which the greater forces required to remove implants may be interpreted as an increase in the strength of bony integration. The purpose of this study was to compare the torque resistance to removal of screw-shaped titanium implants having a dual acid-etched surface (Osseotite) with implants having either a machined surface, or a titanium plasma spray surface that exhibited a significantly more complex surface topography. Three custom screw-shaped implant types - machined, dual acid-etched (DAE), and titanium plasma sprayed (TPS) - were used in this study. Each implant surface was characterized by scanning electron microscopy and optical profilometry. One DAE implant was placed into each distal femur of eighteen adult New Zealand White rabbits along with one of the other implant types. Thus, each rabbit received two DAE implants and one each of the machined, or TPS, implants. All implants measured 3.25 mm in diameter x 4.00 mm in length without holes, grooves or slots to resist rotation. Eighteen rabbits were used for reverse torque measurements. Groups of six rabbits were sacrificed following one, two and three month healing periods. Implants were removed by reverse torque rotation with a digital torque-measuring device. Three implants with the machined surface preparation failed to achieve endosseous integration. All other implants were anchored by bone. Mean torque values for machined, DAE and TPS implants at one, two and three months were 6.00+/-0.64 N-cm, 9.07+/-0.67 N-cm and 6.73+/-0.95 N-cm; 21.86+/-1.37 N-cm, 27.63+/-3.41 N-cm and 27.40+/-3.89 N-cm; and 27.48+/-1.61 N-cm, 44.28+/-4.53 N-cm and 59.23+/-3.88 N-cm, respectively. Clearly, at the earliest time point the stability of DAE implants was comparable to that of TPS implants, while that of the machined implants was an order of magnitude lower. The TPS implants increased resistance to reverse torque removal over the three-month period. The results of this study confirm our previous results that demonstrated enhanced bony anchorage to dual acid-etched implants as compared to machined implants. Furthermore, the present results indicate that dual acid etching of titanium enhances early endosseous integration to a level which is comparable to that achieved by the topographically more complex TPS surfaces.

Analysis of Variance↗
PubMed2003

Variable frequency trains enhance torque independent of stimulation amplitude.

AIM: Variable frequency trains have been reported to enhance force of fatigued human skeletal muscle. More rapid calcium turnover and/or enhanced stiffness may be responsible for the augmented torque-time integral during surface stimulation at moderate amplitude. In contrast, it has recently been suggested that variable frequency train enhancement occurs only at low forces as a result of preferential stimulation of fast fibres and/or altered motor unit recruitment. If correct, this would limit the practical benefit of variable frequency trains. Accordingly, we tested the hypothesis that torque augmentation by variable frequency trains in fatigued skeletal muscle was independent of stimulation amplitude. METHODS: The m. quadriceps femoris of six males was stimulated with constant frequency trains (six 200-micros square waves separated by 70 ms) or variable frequency trains (first interpulse interval 5 ms) at an amplitude that initially evoked approximately 25 or approximately 50% of maximal voluntary isometric torque. RESULTS: After 180 constant frequency trains (50% duty cycle), isometric peak torque decreased approximately 63%. In fatigued muscle, variable frequency trains enhanced the torque-time integral by approximately 23% over that for constant frequency trains and this effect was independent of stimulation amplitude. This was due to greater peak torque and less slowing of rise time. CONCLUSION: These responses show that the torque-time integral can be enhanced at both moderate and high stimulation amplitudes. As such, it is suggested that neither recruitment nor preferential activation of fast muscle is responsible for the "catch-like" property that can be demonstrated in fatigued human skeletal muscle.

Adult↗
PubMed2002

Effectiveness of a lateral-wedge insole on knee varus torque in patients with knee osteoarthritis.

OBJECTIVES: To test whether a lateral-wedged insole, inclined at 5 degrees or 10 degrees, significantly reduces knee varus torque during walking in patients with knee osteoarthritis compared with both using no insole and with wearing nonwedged control insoles of the same material and average thickness. DESIGN: Patients with medial knee osteoarthritis were studied while they walked wearing their comfortable shoes (1) without an insole; (2) with a 5 degrees lateral wedge compared with a nonwedged, 3.175-mm (1/8-in) even-thickness control insole; and (3) with a 10 degrees lateral wedge compared with a nonwedged 6.35-mm ((1/4)-in) even-thickness control insole. SETTING: A gait laboratory with 3-dimensional motion analysis and force platform equipment. PARTICIPANTS: Fifteen patients with clinical and radiographic osteoarthritis of the medial compartment of 1 knee. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Peak external knee varus torques during the stance period of gait. Data regarding lower-extremity joint torques and motions were collected, and knee joint torques using the different insoles and wedges were compared by analysis of variance. RESULTS: Although responses varied among individuals, as a group, both the 5 degrees and 10 degrees lateral-wedge insoles significantly reduced the knee varus torque during walking compared with walking with no insole and walking with nonwedged 3.175-mm and 6.35-mm control insoles. Compared with no insole, the 5 degrees wedge reduced the peak knee varus torque values by about 6% and the 10 degrees wedge reduced the peaks by about 8%. Although there were no significant differences in speed of walking between the conditions, the 10 degrees wedge and 6.35-mm control insoles were associated with varying degrees of discomfort. CONCLUSION: Both wedge insoles are effective in reducing the varus torque during walking beyond what theoretically could be explained by a reduced walking speed or cushioning effect from the insole. These data imply that wedged insoles are biomechanically effective and should reduce loading of the medial compartment in persons with medial knee osteoarthritis. Although the effect of the 5 degrees wedge was smaller, it may be more comfortable than the 10 degrees wedge to wear inside one's own shoes.

Aged↗
PubMed2002

Upper-extremity torque production in men with paraplegia who use wheelchairs.

OBJECTIVES: To study maximal upper-extremity torque values and agonist/antagonist torque ratios in a sample of individuals with paraplegia and to compare these values with a sample of age-, gender-, and weight-matched able-bodied individuals. DESIGN: Cross-sectional, case-control study. SETTING: A biomechanics laboratory. PARTICIPANTS: A convenience sample of 15 men with complete (American Spinal Injury Association class A) T5-L2 paraplegia and 15 able-bodied control subjects. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Maximal isometric torques of 12 upper-extremity muscle groups (shoulder, elbow, and wrist flexion and extension; shoulder abduction and adduction; shoulder internal and external rotation; elbow pronation and supination) were measured with custom dynamometers. RESULTS: Maximal torque values and agonist/antagonist torque ratios for the shoulder, elbow, and wrist functions did not differ between the control subjects and those with complete paraplegia, with the exception of the supination/pronation torque ratio, which was significantly higher in the able-bodied control group. CONCLUSION: Wheelchair propulsion and other functional activities, such as transfers, do not significantly affect maximum torque production of the upper extremities in individuals with paraplegia. On the basis of these findings, arguments that upper-extremity muscle imbalances are important contributory factors to upper-extremity pain and dysfunction in this group may be too simplistic.

Adult↗
PubMedDate not supplied

Influence of bolt tightening torque, wire size, and component reuse on wire fixation in circular external fixation.

OBJECTIVES: To evaluate the effects of bolt torque, wire size, and component reuse on the ability to maintain wire tension in 3 external skeletal fixation systems. STUDY DESIGN: Biomechanical study. METHODS: Yield strength in tension of 1.0-, 1.2-, 1.5-, and 1.6-mm-diameter wires, and yield strength in torque of Hofmann Small Bone Fixation (SBF) cannulated and slotted bolts and IMEX regular and miniature bolts were determined on a testing machine. The minimum bolt tightening torque needed to prevent wire slippage at clinically recommended wire tensions was determined. Components were tested 10 times, and loads at slippage were recorded. RESULTS: The IMEX system required a mean of 8 Nm of bolt tightening torque to maintain 900 N (1.6-mm wires). The SBF system required a mean of 3 Nm bolt torque to maintain 300 N (1.0-mm wires) and 5 Nm to maintain 600 N (1.2-mm wires). The SBF cannulated bolt required 9 Nm of torque to maintain 900 N (1.5-mm wires). The SBF slotted bolts could only maintain 800 N before yield. The IMEX miniature system required a mean bolt torque of 1.1 Nm to maintain 300 N. The cannulated and slotted bolts from both manufacturers failed to maintain 70% of initial wire tension after 7 and 4 uses, respectively. CONCLUSIONS: The IMEX systems and the SBF system using 1.0- and 1.2-mm wires could maintain clinically recommended wire tension safely. Only the IMEX system could maintain clinically recommended wire tension safely using 1.5- or 1.6-mm wires. CLINICAL RELEVANCE: The SBF system using 1.0- and 1.2-mm wires and the IMEX system using all wire sizes can maintain clinically relevant wire tension. The SBF system using 1.5-mm wires could not. Cannulated and slotted bolts should not be used more than 6 and 3 times, respectively. Nuts should not be reused.

Animals↗
PubMed2002

Velocity-dependent ankle torque in rats after contusion injury of the midthoracic spinal cord: time course.

Progressive neurophysiological changes in the excitability of the pathways that subserved ankle extensor stretch reflexes were observed following midthoracic contusion. The purpose of the present study was to determine the nature and time course of velocity-dependent changes in the excitability of the ankle stretch reflex following T(8) contusion injury. These studies were conducted in adult Sprague-Dawley rats using a 10-g 2.5-cm weight drop onto the exposed thoracic spinal cord (using an NYU injury device and a MASCIS protocol). Velocity-dependent ankle torques and triceps surae EMGs were measured in awake animals over a broad range of rotation velocities (49-612 deg/sec) using instrumentation and protocol previously reported. EMGs and ankle torques were measured before and at weekly intervals following injury. Statistical tests of the data included within group repeated measures ANOVA and between group one-way ANOVA comparisons with time-matched control animals. An alternating pattern of significant increase followed by significant decrease in velocity-dependent ankle torque was observed during the first postinjury month. An increase of 33% in the peak torque and 24% in peak EMG magnitude at 612 deg/sec was observed in the first week. EMG burst amplitudes, that were timed-locked to the dynamic phase of the rotation, were observed to increase and decrease in a manner, which indicated that the changes in torque included stretch-evoked active contractions of the ankle extensors. During the second and third postinjury months, consistent 24-40% increases in the peak torques and 17-107% increases in the EMG magnitudes at the highest velocity were observed. No significant increases in torques were observed in the slowest rotation velocity in these periods.

Animals↗
PubMed1997

Eccentric peak torque of the plantar and dorsiflexors is maintained in older women.

Although a relative preservation of eccentric (ECC) strength with age has been reported previously, this phenomenon has not been studied in lower leg muscles. Concentric (CONC) and ECC plantar (PF) and dorsiflexion (DF) in healthy active older women (OW; n = 16, age = 67 +/- 4 years) and younger women (YW; n = 16, age = 27 +/- 4 years) were studied. Passive resistive torque of the plantar flexors and average rate of torque development (RTD) for both DF and PF were also measured. The OW had CONC peak torques that were 74% and 89% of the YW for PF and DF, whereas ECC peak torques were 97% and 100% of the YW. ECC torque patterns were almost identical for both groups, but there were significant differences for passive resistive torque (OW > YW; p < .01) and CONC RTD (OW < YW; p < .05). While increased passive resistive torque did not prove to be influential in maintaining ECC strength with age, it had a negative effect on CONC DF function.

Adult↗
PubMed2000

Torque during canal instrumentation using rotary nickel-titanium files.

Nickel-titanium engine-driven rotary instruments are used increasingly in endodontic practice. One frequently mentioned problem is fracture of an instrument in the root canal. Very few studies have been conducted on torsional characteristics of these instruments, and none has been done under dynamic conditions. The purposes of this study were to measure the torque generated and the apical force applied during instrumentation with a commercial engine-driven nickel-titanium file system, and to relate torque generated during simulated clinical use to torsional failure of the instruments. Ten extracted human teeth (five with small-sized and five with medium-sized straight root canals) were instrumented with Quantec Series 2000 files, and the torque and apical force generated were measured. The applied apical force was generally low, not exceeding 150 g in either small or medium canals. The torque depended on the tip size and taper of each instrument, and on canal size. Instruments with 0.05 and 0.06 taper generated the highest torque, which was greater in small than in medium canals. The torque at failure was significantly (p < 0.001) higher than torque during instrumentation, but with considerable variation in the extent of the difference.

Analysis of Variance↗
PubMed2005

Overcoming abnormal joint torque patterns in paretic upper extremities using triceps stimulation.

The goal of this research project was to quantitatively assess whether transcutaneous triceps stimulation can overcome the expression of abnormal torque patterns in the paretic upper limb of subjects with hemiparetic stroke. Abnormal torque patterns consist of strong coupling between shoulder abduction (SAB) and elbow flexion (EF) or between elbow extension (EE) and shoulder adduction (SAD) torques. Both patterns reduce the active range of motion during arm movements. Eight chronic stroke subjects with moderate to severe (Fugl-Meyer assessment scores of 21/66-36/66) upper limb motor impairment participated in this study. Shoulder and elbow joint torques were measured with a 6-degrees-of-freedom load cell under isometric conditions, while the triceps muscle was stimulated to generate EE torques. At the same time the subjects were asked to lift up their arm to generate different SAB torque levels. The obtained isometric results showed that electrical stimulation can overcome abnormal torque patterns in chronic stroke subjects while generating SAB. This is likely to have potential benefits to increase the reaching workspace of the paretic arm.

Adult↗
PubMed2005

Length-dependent changes in voluntary activation, maximum voluntary torque and twitch responses after eccentric damage in humans.

To assess the contribution of central and peripheral factors to changes in maximum voluntary force and its length dependence after eccentric muscle damage, voluntary and twitch torque were measured across a wide angular range, along with voluntary activation using twitch interpolation. Isometric torque from both maximum voluntary contractions (MVCs) and paired twitches to motor nerve stimulation were measured from 60 to 150 deg elbow flexion in 10 deg increments in eight subjects. Optimal angles were determined by curve fitting. Each subject then performed eccentric contractions until voluntary torque had decreased by approximately 40%. Measurements were repeated at 2 h, 1 day and 8 days post-exercise to follow acute and longer-term changes. Before exercise, the optimal angle was in the mid-range (93+/-10 deg; mean+/-s.d.) for MVCs, and at a more extended elbow angle for the twitch (106+/-6 deg, P < 0.05). Voluntary activation was generally high (> 94%) but depended on elbow angle, with activation being approximately 4% lower at the most flexed compared to the most extended angle. Two hours after exercise, MVCs decreased 40%, while twitch torque declined 70%. All subjects showed a shift in optimal angle to longer muscle lengths for MVCs (17+/-16 deg at 2 h, 14+/-7 deg at day 1, P < 0.05). This shift contributed minimally (approximately 3%) to the reduction in torque at 90 deg, as the torque-angle relation was relatively flat around the optimum. The twitch showed a smaller shift (approximately 4 deg) to longer lengths which was not statistically significant. Voluntary activation was significantly impaired in the early stages after exercise (2 h and day 1, P < 0.05), particularly at short muscle lengths. By 8 days after exercise, the optimal angle had returned to pre-exercise values, but MVC, twitch torque and voluntary activation had not fully recovered. Eccentric exercise causes a short-term shift in the optimal angle for MVCs and produces a length-dependent impairment in voluntary activation. Therefore, it appears that both central and peripheral factors limit muscle performance following eccentric damage, with limits to voluntary drive being especially important at short lengths.

Adult↗
PubMed2006

Influence of shoulder abduction and lateral trunk tilt on peak elbow varus torque for college baseball pitchers during simulated pitching.

Elbow varus torque is a primary factor in the risk of elbow injury during pitching. To examine the effects of shoulder abduction and lateral trunk tilt angles on elbow varus torque, we conducted simulation and regression analyses on 33 college baseball pitchers. Motion data were used for computer simulations in which two angles-shoulder abduction and lateral trunk tilt-were systematically altered. Forty-two simulated motions were generated for each pitcher, and the peak elbow varus torque for each simulated motion was calculated. A two-way analysis of variance was performed to analyze the effects of shoulder abduction and trunk tilt on elbow varus torque. Regression analyses of a simple regression model, second-order regression model, and multiple regression model were also performed. Although regression analyses did not show any significant relationship, computer simulation indicated that the peak elbow varus torque was affected by both angles, and the interaction of those angles was also significant. As trunk tilt to the contralateral side increased, the shoulder abduction angle producing the minimum peak elbow varus torque decreased. It is suggested that shoulder abduction and lateral trunk tilt may be only two of several determinants of peak elbow varus torque.

Abdomen↗
PubMed2000

Age causes a redistribution of joint torques and powers during gait.

At self-selected walking speeds, elderly compared with young adults generate decreased joint torques and powers in the lower extremity. These differences may be actual gait-limiting factors and neuromuscular adaptations with age or simply a consciously selected motor pattern to produce a slower gait. The purpose of the study was to compare joint torques and powers of young and elderly adults walking at the same speed. Twelve elderly and fourteen young adults (ages 69 and 21 yr) walked at 1.48 m/s over a force platform while being videotaped. Hip, knee, and ankle torques and powers were calculated from the reaction force and kinematic data. A support torque was calculated as the sum of the three joint torques. Extensor angular impulse during stance and positive work at each joint were derived from the torques and powers. Step length was 4% shorter and cadence was 4% higher in elderly adults (both P < 0.05) compared with young adults. Support angular impulse was nearly identical between groups, but elderly adults had 58% greater angular impulse and 279% more work at the hip, 50% less angular impulse and 39% less work at the knee, and 23% less angular impulse and 29% less work at the ankle compared with young adults (t-test, all P < 0.05). Age caused a redistribution of joint torques and powers, with the elderly using their hip extensors more and their knee extensors and ankle plantar flexors less than young adults when walking at the same speed. Along with a reduction in motor and sensory functions, the natural history of aging causes a shift in the locus of function in motor performance.

Adult↗
PubMed2007

Postactivation potentiation in a human muscle: effect on the rate of torque development of tetanic and voluntary isometric contractions.

Postactivation potentiation (PAP), a mechanism by which the torque of a muscle twitch is increased following a conditioning contraction, is well documented in muscular physiology, but little is known about its effect on the maximal rate of torque development and functional significance during voluntary movements. The objective of this study was to investigate the PAP effect on the rate of isometric torque development of electrically induced and voluntary contractions. To that purpose, the electromechanical responses of the thumb adductor muscles to a single electrical stimulus (twitch), a train of 15 pulses at 250 Hz (HFT(250)), and during ballistic (i.e., rapid torque development) voluntary contractions at torque levels ranging from 10 to 75% of maximal voluntary contraction (MVC) were recorded before and after a conditioning 6-s MVC. The results showed that the rate of torque development was significantly (P < 0.001) increased after the conditioning MVC, but the effect was greater for the twitch ( approximately 200%) compared with the HFT(250) ( approximately 17%) or ballistic contractions (range: 9-24%). Although twitch potentiation was maximal immediately after the conditioning MVC, maximal potentiation for HFT(250) and ballistic contractions was delayed to 1 min after the 6-s MVC. Furthermore, the similar degree of potentiation for the rate of isometric torque development between tetanic and voluntary ballistic contractions indicates that PAP is not related to the modality of muscle activation. These observations suggest that PAP may be considered as a mechanism that can influence our contractions during daily tasks and can be utilized to improve muscle performance in explosive sports.

Adaptation, Physiological↗
PubMed2005

Neuromuscular adaptation during skill acquisition on a two degree-of-freedom target-acquisition task: isometric torque production.

In this study we attempted to identify the principles that govern the changes in neural control that occur during repeated performance of a multiarticular coordination task. Eight participants produced isometric flexion/extension and pronation/supination torques at the radiohumeral joint, either in isolation (e.g., flexion) or in combination (e.g., flexion-supination), to acquire targets presented by a visual display. A cursor superimposed on the display provided feedback of the applied torques. During pre- and postpractice tests, the participants acquired targets in eight directions located either 3.6 cm (20% maximal voluntary contraction [MVC]) or 7.2 cm (40% MVC) from a neutral cursor position. On each of five consecutive days of practice the participants acquired targets located 5.4 cm (30% MVC) from the neutral position. EMG was recorded from eight muscles contributing to torque production about the radiohumeral joint during the pre- and posttests. Target-acquisition time decreased significantly with practice in most target directions and at both target torque levels. These performance improvements were primarily associated with increases in the peak rate of torque development after practice. At a muscular level, these changes were brought about by increases in the rates of recruitment of all agonist muscles. The spatiotemporal organization of muscle synergies was not significantly altered after practice. The observed adaptations appear to lead to performances that are generalizable to actions that require both greater and smaller joint torques than that practiced, and may be successfully recalled after a substantial period without practice. These results suggest that tasks in which performance is improved by increasing the rate of muscle activation, and thus the rate of joint torque development, may benefit in terms of the extent to which acquired levels of performance are maintained over time.

Adaptation, Physiological↗