Physical Function After Total Knee Replacement: An Observational Study Describing Outcomes in a Small Group of Women From China and the United States.

OBJECTIVE: To describe physical function before and six months after Total Knee Replacement (TKR) in a small sample of women from China and the United States. DESIGN: Observational. SETTING: Community environment. OUTCOMES: Both groups adhered to the Osteoarthritis Research Society International (OARSI) protocols for the 6-minute walk and 30-second chair stand. We compared physical function prior to TKR and 6 months after using linear regression adjusted for covariates. PARTICIPANTS: Women (N=60) after TKR. INTERVENTIONS: Not applicable. RESULTS: Age and body mass index in the China group (n=30; 66y and 27.0kg/m2) were similar to those in the U.S. group (n=30; 65y and 29.6kg/m2). Before surgery, the China group walked 263 (95% confidence interval [CI], -309 to -219) less meters and had 10.2 (95% CI, -11.8 to -8.5) fewer chair stands than the U.S. group. At 6 months when compared with the U.S. group, the China group walked 38 more meters, but this difference did not reach statistical significance (95% CI, -1.6 to 77.4), and had 3.1 (95% CI, -4.4 to -1.7) fewer chair stands. The China group had greater improvement in the 6-minute walk test than did the U.S. group (P<.001). CONCLUSIONS: Despite having worse physical function before TKR, the China group had greater gains in walking endurance and similar gains in repeated chair stands than did the U.S. group after surgery.

Sit-To-Stand Biomechanics Before and After Total Hip Arthroplasty.

The purpose of this study was to evaluate changes in movement patterns during a sit-to-stand (STS) task before and after total hip arthroplasty (THA), and to compare biomechanical outcomes after THA to a control group. Forty-five subjects who underwent THA and twenty-three healthy control subjects participated in three-dimensional motion analysis. Pre-operatively, subjects exhibited inter-limb movement asymmetries with lower vertical ground reaction force (VGRF) and smaller moments on the operated limb. Although there were significant improvements in movement symmetry 3 months after THA, patients continued to demonstrate lower VGRF and smaller moments on the operated limb compared to non-operated and to control limbs. Future studies should identify the contributions of physical impairments and the influence of surgical approach on STS biomechanics.

THE EFFECT OF TRAINING ON A COMPLIANT SURFACE ON MUSCLE ACTIVATION AND CO-CONTRACTION AFTER ANTERIOR CRUCIATE LIGAMENT INJURY.

BACKGROUND: Performing physical activities on compliant surfaces alters joints kinematics by decreasing joint motions. However, the effect of administering a training program on a compliant surface on muscle activities after anterior cruciate ligament (ACL) injury is unknown. HYPOTHESIS/PURPOSE: To compare the effects of training on a compliant surface and manual perturbation training on individual muscle activation and muscle co-contraction indexes after an ACL injury. It was hypothesized that patients who received training on the compliant surface would demonstrate higher individual and combined muscle activities compared to the manual group. METHOD: Sixteen patients (participated in level I/II sports) who sustained an ACL injury and had not undergone reconstructive surgery participated in this preliminary study. Eight patients received training on a compliant surface (Compliant group) and data of eight patients matched by age and sex from a previous study who received manual perturbation training were used as a control group (Manual group). Patients in both groups completed standard three-dimensional gait motion analysis with surface electromyography (EMG) of several lower extremity muscles during gait. Muscle co-contraction index and individual muscle activations were computed during weight acceptance (WA) and mid-stance (MS) intervals. A 2x2 analysis of variance (ANOVA) was used with an alpha level of p<0.10 to account for the high EMG variability. RESULTS: The compliant group significantly increased muscle co-contraction of vastus lateralis-lateral hamstring (VL-LH), vastus medialis-gastrocnemius medialis (VM-MG), and vastus lateralis (VL) muscle activity during WA (p ≤ 0.035) and manual group significantly decreased VM-MG muscle co-contraction during WA (p=0.099) after training. CONCLUSION: Administering training on a compliant surface provides different effects on muscle activation compared to manual perturbation training after an ACL injury. Training on a compliant surface caused increased muscle co-contraction indexes and individual muscle activation, while manual perturbation training decreased the VM-MG muscle co-contraction index. LEVEL OF EVIDENCE: 2b.

Lower extremity work along with triceps surae structure and activation is altered with jumping after Achilles tendon repair.

Achilles tendon rupture leads to long term plantar flexor deficits. The purpose of this study was to describe changes in jumping biomechanics along with triceps surae structure and activation in individuals after Achilles repair. Eleven individuals 1-3 years following Achilles repair and 10 healthy controls were included. Kinetics and kinematics, analyzed using a constituent lower extremity work (CLEW) approach, and muscle activity using surface electromyography (EMG) were collected during a unilateral hopping task. Triceps surae myotendinous structure was assessed using ultrasound imaging. There were no differences in jump height, absolute limb work, or cost of transport between groups. During takeoff, the knee did more (p < 0.001) and ankle did less concentric work (p < 0.001), and lateral gastrocnemius rate of rise was higher (p = 0.02) on the ruptured side. During landing, the knee did more eccentric work (p = 0.033) and lateral gastrocnemius (p = 0.003) and soleus (p = 0.02) activation amplitude prior to landing was higher on the ruptured side. Individuals after Achilles tendon repair shift work toward the knee and alter muscle recruitment. Differences in lateral gastrocnemius activity may indicate that it is well-situated to generate power during takeoff and assist in landing with the soleus. The lack of change in muscle activity and decreased cross sectional area of the medial gastrocnemius may suggest that this muscle atrophies and does not accommodate to the hopping task. Clinical Significance: Proximal lower extremity strengthening along with emphasizing medial gastrocnemius and soleus activation during the recovery of patients with Achilles tendon repair may be rehabilitative targets for improved jumping performance. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Neural training for quick strength gains in the elderly: strength as a learned skill.

A sample of 20 older adults (76 +/- 6 years) participated in a two-session training intervention with the goal of eliciting rapid and functionally meaningful strength gains in the ankle plantarflexors. Tests were conducted on a Monday-Wednesday-Friday schedule with two training sessions after tests one and two. During each test, subjects performed five maximal explosive force production contractions (MVCs) from which maximal voluntary torque (MVT) and peak rates of torque development (RTDs) were obtained. To augment the quick strength gains typically observed in response to serial strength measurements, these MVCs were supplemented with exercises consisting of high-velocity, low-force movements at the ankle joint. These exercises were chosen to elicit high rates of neural stimulation without high resistance. Maximal voluntary torque increased by 15% from 53.9 +/- 36 to 62.2 +/- 36.2 N x m (p = 0.02). There was a parallel trend toward increases in RTD based on RTD measures computed over various timescales (0.11 < p < 0.21). The nonsignificant increase in RTD was from 223.9 +/- 153.6 to 248.4 +/- 147.8 N x m x s(-1). This preliminary study has determined that rapid strength gains of functional magnitude are possible in the plantarflexors of the elderly. Subsequent work is necessary to test the translation of such gains to function in the frail elderly and to determine the specific contributions of the selected low-resistance exercises to overall gains.

Activity Demands During Multi-Directional Team Sports: A Systematic Review.

BACKGROUND: Late-stage rehabilitation programs often incorporate 'sport-specific' demands, but may not optimally simulate the in-game volume or intensity of such activities as sprinting, cutting, jumping, and lateral movement. OBJECTIVE: The aim of this review was to characterize, quantify, and compare straight-line running and multi-directional demands during sport competition. DATA SOURCES: A systematic review of PubMed, CINAHL, SPORTDiscus, and Cochrane Central Register of Controlled Trials databases was conducted. STUDY ELIGIBILITY CRITERIA: Studies that reported time-motion analysis data on straight-line running, accelerations/decelerations, activity changes, jumping, cutting, or lateral movement over the course of an entire competition in a multi-directional sport (soccer, basketball, lacrosse, handball, field hockey, futsal, volleyball) were included. STUDY APPRAISAL AND SYNTHESIS METHODS: Data was organized based on sport, age level, and sex and descriptive statistics of the frequency, intensity, time, and volume of the characteristics of running and multi-directional demands were extracted from each study. RESULTS: Eighty-one studies were included in the review (n = 47 soccer, n = 11 basketball, n = 9 handball, n = 7 field hockey, n = 3 futsal, n = 4 volleyball). Variability of sport demand data was found across sports, sexes, and age levels. Specifically, soccer and field hockey demanded the most volume of running, while basketball required the highest ratio of high-intensity running to sprinting. Athletes change activity between 500 and 3000 times over the course of a competition, or once every 2-4 s. Studies of soccer reported the most frequent cutting (up to 800 per game), while studies of basketball reported the highest frequency of lateral movement (up to 450 per game). Basketball (42-56 per game), handball (up to 90 per game), and volleyball (up to 35 per game) were found to require the most jumping. LIMITATIONS: These data may provide an incomplete view of an athlete's straight-line running load, considering that only competition and not practice data was provided. CONCLUSIONS: Considerable variability exists in the demands of straight-line running and multi-directional demands across sports, competition levels, and sexes, indicating the need for sports medicine clinicians to design future rehabilitation programs with improved specificity (including the type of activity and dosage) to these demands.

Lower leg compensatory strategies during performance of a step up and over task in patient six-months after total knee arthroplasty.

The purpose of this study was to assess the ankle, knee, and hip joint contributions to the total support moment (TSM) and the activation patterns of muscles in the lower leg in patients after total knee arthroplasty (TKA) and healthy older adults during the step up and over task. Moreover, the relationship between quadriceps strength and knee contribution to TSM was measured. Twenty patients six-months after TKA and twenty healthy controls were recruited for this study. Motion and surface electromyographic (EMG) analyses were performed during a step up and over task. Biomechanics and EMG variables were compared between groups using ANCOVA models with movement speed as covariate. Patients after TKA had reduced contribution to the TSM from the knee joint, and greater contribution from the hip and ankle joints, possibly to compensate for the reduced contribution at the knee. No consistent differences of EMG activation or co-contraction were found between groups. Patients with stronger quadriceps had significantly higher knee contribution to TSM during the lowering phase of the task. The results of this study suggest that patients after TKA may use compensatory strategies at the hip and ankle joints to safely perform the step up and over task. Patients may rely on the force generating ability of the quadriceps during the lowering phase as they are not able to compensate with other joints of the lower extremity during this phase of the task.

Activation deficits do not limit quadriceps strength training gains in patients after total knee arthroplasty.

PURPOSE/BACKGROUND: Patients after total knee arthroplasty (TKA) are known to exhibit deficits in quadriceps muscle activation. The purpose of this study was to determine if quadriceps activation levels in patients after TKA at the beginning of rehabilitation would influence quadriceps strength after rehabilitation. DESIGN: A secondary analysis of data from a prospective, randomized, longitudinal clinical trial. SETTING: Institutional clinic and research laboratory. PARTICIPANTS: Patients who underwent unilateral TKA (Men= 102; Female= 84). MAIN OUTCOME: Voluntary activation of the quadriceps during maximal voluntary isometric contractions (MVIC) was measured using the central activation ratio (CAR). Hierarchical multivariate regression analysis was used to determine if CAR prior to treatment could predict MVIC after the strength training intervention. RESULTS: After controlling for age, sex, and initial strength levels (R(2)= 0.548; p<0.001), the predictability of quadriceps strength after the 6-week intervention did not change when pain during MVIC (R(2)= 0.551; p= 0.317) and pre-rehabilitation activation levels (R(2)= 0.551; p= 0.818) were introduced into the regression. CONCLUSIONS: Initial quadriceps activation levels, for patients who underwent TKA, did not predict the quadriceps strength following a strength training intervention. Therefore, deficits in voluntarily activation post-operatively should not be considered as a rate-limiting factor in recovering quadriceps strength after TKA. LEVEL OF EVIDENCE: Retrospective cohort study. Level IIb.

Associations between knee extensor power and functional performance in patients after total knee arthroplasty and normal controls without knee pain.

PURPOSE/BACKGROUND: Deficits in functional abilities persist after total knee arthroplasty (TKA), while static measures of knee extensor strength (e.g. isometric contractions) are related to functional performance, little is known about the associations between functional ability and dynamic knee extensor strength (e.g. power). With the growing rate of these procedures, in a progressively younger and more active cohort, a better understanding of the functional importance of dynamic strength (muscle power) is needed. The purpose of this study was to examine the associations between functional performance and peak knee extensor power (isokinetic and isotonic measures) from patients after unilateral TKA. DESIGN: Cross-sectional, controlled laboratory study, with correlation and regression analyses. SETTING: Institutional clinic and research laboratory. PARTICIPANTS: Patients 6 months after TKA (N=24, 12 men and women), most of whom were mildly to very active. A normal control group without knee pain (CON; N=22, 10 men and 12 women) was also assessed for comparison. MAIN OUTCOME MEASURES: Static and dynamic strength measures were assessed during normalized voluntary isometric contractions (NMVIC), isokinetic contractions at three velocities (60, 90, and 120 deg/s), and isotonic contractions against three body weight normalized resistances (20, 30 and 40% BW). Functional performance was assessed using the timed up-and-go (TUG), stair climbing test (SCT), and 6- minute walk (6MW). Analyses of the relationships between functional performance measures and peak knee extensor NMVIC and power were performed. Regression analyses predicting functional performance from power were also performed after controlling for NMVIC. RESULTS: Peak power across isokinetic velocities, isotonic resistances, and NMVICs were correlated with the functional performance measures for the TKA group. Unlike the TKA group, functional performance was not significantly associated with peak power across all isokinetic velocities and isotonic resistances (e.g no significant associations between peak isotonic power and 6MW distance). In the TKA group, inclusion of the isotonic power against 30% BW, after controlling for NMVIC, improved the predictability of all three functional performance tests; TUG (p= 0.022), SCT (p=0.006), and 6MW (p=0.001). CONCLUSIONS: Measurements of knee extensor power may be a useful tool for clinicians when assessing and setting milestones during rehabilitation. LEVEL OF EVIDENCE: Prospective cohort study, level II.

Perception and presentation of function in patients with unilateral versus bilateral knee osteoarthritis.

OBJECTIVE: Lower extremity functional performance and perception of functional abilities influence clinical management in people diagnosed with unilateral or bilateral knee osteoarthritis (OA). The purpose of this study was to determine if there were differences in perception of function and performance during functional tasks between individuals with unilateral and bilateral knee OA. METHODS: The functional abilities of patients with symptomatic and radiographic diagnosed unilateral (n = 84) or bilateral (n = 68) knee OA were evaluated with self-report measures and performance-based tests. Self-report measures included the Knee Outcome Survey, the Global Rating Scale, and the physical component of the Short Form 36 health survey; functional tests included the Timed Up-and-Go Test, the Stair Climbing Test, and the 6-Minute Walk Test. Multivariate analyses of variance were performed separately for men and women to determine if perception (self-report measures) and performance (functional tests) were dependent on the number of involved knees. RESULTS: No significant main effects were observed in functional performance between groups for either sex. Similarly, the perception measures did not differ between groups. In general, individuals diagnosed with unilateral and bilateral knee OA both performed functional tasks and perceived their functional ability similarly. CONCLUSION: Regardless of the number of involved knees, individuals with knee OA perform and perceive their functional ability similarly, which suggests that clinicians need to consider other factors, such as how long the disease has been progressing or how functional abilities have changed, when treating patients with knee OA.

The validity of plantarflexor strength measures obtained through hand-held dynamometry measurements of force.

PURPOSE/BACKGROUND: Hand-held dynamometers are commonly used to assess plantarflexor strength during rehabilitation. The purpose of this study was to determine the concurrent validity of measuring plantarflexion force using a hand-held dynamometer (HHD) as compared to an electromechanical dynamometer as the gold standard. The hypothesis was that plantarflexor forces obtained using a hand-held dynamometer would not show absolute agreement with a criterion standard. DESIGN: Concurrent validity assessment for a diagnostic strength testing device. SETTING: Institutional clinic and research laboratory. PARTICIPANTS: Volunteer sample of healthy university students (N=20, 10 women, 10 men; 25.9±4.1 years). MAIN OUTCOME MEASURES: Maximal plantarflexion strength was measured using both a HHD and an electromechanical dynamometer (EMD) as a criterion measure. RESULTS: Plantarflexor force measures with the HHD were significantly different (p<0.01) and not correlated with plantarflexor forces measured using the EMD for either limb (R(2) ≤ 0.09). CONCLUSIONS: Plantarflexor strength measurements acquired using HHD are different from those acquired using an EMD and are likely influenced by the strength of the examiner. LEVEL OF EVIDENCE: Prospective cohort study, level II.

Quantifying Neuromuscular Electrical Stimulation Dosage after Knee Arthroplasty.

Recovering functional ability after total knee arthroplasty (TKA) requires recovery of strength and voluntary activation. Short-term recovery of strength and activation are enhanced following a protocol combining strength training with neuromuscular electrical stimulation (NMES). The purpose of the study was to determine if a dose response curve could be constructed for patients who received NMES as part of their treatment after TKA. NMES dosage was quantified as the electrically evoked knee extensor torque, expressed as a percentage of the subject's maximal voluntary contraction. Dose-response curves were generated, with the associations between NMES training intensity and quadriceps strength, voluntary activation, and lean muscle cross-sectional area examined using Pearson Product-Moment Correlation Coefficients. Significantly, linear correlations were observed between NMES training intensity and both quadriceps strength and voluntary activation, but not lean muscle cross-sectional area. These results suggest that maximizing the elicited training force during rehabilitation will enhance short-term recovery following TKA.

Practicing a functional task improves steadiness with hand muscles in older adults.

INTRODUCTION: Improvements in steadiness with practice have been associated with enhanced performance on a functional task in old adults. PURPOSE: The aims of the study were to examine the specificity of the association between steadiness and a functional task and to assess the influence of practicing a functional task on force steadiness of hand muscles. METHODS: Twenty-three older adults (≥70 yr) participated in the study and were assigned to either a practice group (n = 15) or a control group (n = 8). Subjects completed two testing sessions that were 2 wk apart. The practice group completed six additional sessions to practice a functional task (Grooved Pegboard). Tests included maximal voluntary contractions (MVC), force steadiness (precision pinch and index finger abduction) at three target forces (5%, 15%, and 25% MVC), and the Grooved Pegboard test. The associations between strength, steadiness, and the time needed to complete the Grooved Pegboard test were examined. In addition, MVC force, steadiness, and pegboard time were compared between the two testing sessions. RESULTS: The time needed to complete the Grooved Pegboard test was associated with index finger abduction steadiness for two of the three target forces (15% and 25% MVC) but was not associated with pinch steadiness. Practice significantly reduced the time needed to complete the Grooved Pegboard test and improved steadiness in both tasks. CONCLUSIONS: Force steadiness provides an appropriate index of hand function, especially when measured at low forces.

Associations among strength, steadiness, and hand function across the adult life span.

INTRODUCTION: Age-related differences in force steadiness have been extensively examined and used as an index of motor function. However, the functional relevance of steadiness remains unclear. PURPOSE: The aim here was to evaluate the relations among hand strength, steadiness, and function across the adult life span. METHODS: Seventy-five adults (45 women; 18-89 yr) performed three strength, two steadiness, and four functional tests with both hands. Strength was measured during index finger abduction, precision pinch, and handgrip, and steadiness was measured during index finger abduction and precision pinch. Functional tests included the Grooved Pegboard test, the game Operation™, a scissor task, and a tracing task. RESULTS: Moderate correlations were observed between both steadiness tasks and performance on the Grooved Pegboard test (R(2) = 0.57 and R(2) = 0.46, respectively) and Operation™ (R(2) = -0.47 and R(2) = -0.57, respectively). CONCLUSIONS: The relation between measures of steadiness and hand function suggests that the physiological mechanisms responsible for differences in steadiness also contribute to differences in the performance of fine motor tasks with the hand.

Time course of quad strength, area, and activation after knee arthroplasty and strength training.

INTRODUCTION: changes in strength, activation, and morphology of the quadriceps femoris muscle group were assessed in 61 individuals that underwent unilateral total knee arthroplasty, with progressive postoperative strength training, for primary knee osteoarthritis. METHODS: assessments of these three parameters were made at four time points (preoperatively and 4, 12, and 52 wk postoperatively). Maximal voluntary knee extension strength was recorded using an electromechanical dynamometer, and voluntary muscle activation was measured using a burst superimposition technique. Lean muscle cross-sectional area (CSA) was determined using magnetic resonance imaging. RESULTS: preoperatively, the surgical limb was significantly weaker and smaller than the nonsurgical limb. Strength, voluntary muscle activation, and CSA of the quadriceps femoris significantly improved over the study period. At 52 wk, the surgical limb was still significantly smaller than the nonsurgical limb but had greater levels of voluntary muscle activation. In the nonsurgical limb, CSA was the primary determinant of strength across all time points, with voluntary muscle activation progressively contributing more from the preoperative assessment (R = 0.11) to the assessment 52 wk postoperatively (R = 0.26). In the surgical limb, voluntary muscle activation was the primary determinant of strength preoperatively and 4 wk postoperatively (R = 0.38 and 0.41, respectively), whereas CSA was the primary determinant of quadriceps strength 12 and 52 wk postoperatively (R = 0.44). CONCLUSION: resolving the impairments in voluntary muscle activation after total knee arthroplasty may be necessary before visible gains in strength and muscle hypertrophy are evident.

Comparison of the influence of two stressors on steadiness during index finger abduction.

Although several stressors have been used to examine the influence of arousal on motor performance, including noxious electrical stimulation, cold pressor test, and mental math calculations, no study has compared the influence of different physical stressors on motor output. The purpose of the study was to compare the influence of two stressors (cold pressor test and electrical stimulation) on the steadiness of the abduction force exerted by the index finger. Sixteen subjects (22.8+/-3.5 years, 8 women) performed steadiness trials before (anticipatory phase), during (stressor phase), and after (recovery phase) each stressor. The steadiness task involved isometric contractions with the first dorsal interosseus muscle, which is the muscle that produces most of the abduction force exerted by the index finger. Subjects were required to match the abduction force on a monitor to a target force set to 5% of the maximal voluntary contraction (MVC) force for 60s. In contrast to previous studies that examined the influence of stressors on pinch grip steadiness, the two stressors did not decrease steadiness. Furthermore, the absence of a change in steadiness contrasted with the increases in cognitive (State-Trait Anxiety Index, Visual Analog Scale) and physiological (heart rate) arousal during the stressor phase and the subsequent decline during recovery. The null effect of the stressors on index finger steadiness may be due to the relative simplicity of the task compared with those examined previously.

Short term auditory pacing changes dual motor task coordination in children with and without dyslexia.

This study examined the effect of short-term auditory pacing practice on dual motor task performance in children with and without dyslexia. Groups included dyslexic with Movement Assessment Battery for Children (MABC) scores > 15th percentile (D_HIGH, n = 18; mean age 9.89 +/- 2.0 years), dyslexic with MABC < or = 15th percentile (D_LOW, n = 15; mean age 10.43 +/- 1.8 years), and typically developing (TD, n = 18; mean age 10.64 +/- 1.8 years). Participants clapped and walked simultaneously for 3 pretest trials, completed 16 trials with auditory pacing, and 3 posttest trials without pacing. D_LOW differed significantly from D_HIGH and TD in mean relative phase (MRP) of the clap relative to the step, and variability (VRP) of the MRP. Significant differences also existed between pretest blocks and all other blocks in MRP. The results suggest that a short-term auditory pacing may be effective in improving MRP in all children. Further, there may be subtypes of dyslexia wherein children have more profound coordination difficulties and may preferentially change dual motor task performance with auditory pacing.

Recruitment and derecruitment characteristics of motor units in a hand muscle of young and old adults.

The significant decline in motor neuron number after approximately 60 yr of age is accompanied by a remodeling of the neuromuscular system so that average motor unit force increases and the ability of old adults to produce an intended force declines. One possible explanation for the loss of movement precision is that the remodeling increases the difference in recruitment forces between successively recruited motor units in old adults and this augments force variability at motor unit recruitment. The purpose of the study was to compare the forces and discharge characteristics of motor units in a hand muscle of young and old adults at motor unit recruitment and derecruitment. The difference in recruitment force between pairs of motor units did not differ between young (n=54) and old adults (n=56; P=0.702). However, old adults had a greater proportion of contractions in which motor units discharged action potentials transiently before discharging continuously during the ramp increase in force (young: 0.32; old: 0.41; P=0.045). Force variability at motor unit recruitment was greater for old adults compared with young adults (Por=0.729). These results suggest that the difference in force between the recruitment of successive motor units does not differ between age groups, but that motor unit recruitment may be more transient and could contribute to the greater variability in force observed in old adults during graded ramp contractions.

Postcontraction errors in isometric force control.

Subjects learned to produce brief isometric force pulses that were 10% of their maximal voluntary contraction (MVC) force. Subjects became proficient at performing sets of 10 pulses within boundaries of 8-12% MVC, with visual feedback and without (kinesthetic sense). In both the control (Con, n = 10) and experimental (Exp, n = 20) groups, subjects performed two sets of 10 kinesthetically guided pulses. Subjects then either performed a 10-s MVC (Exp) or remained at rest (Con) between sets. Following the MVC, Exp subjects had force errors of +30%, whereas performance was maintained in Con. There was evidence for both muscular and neural contributions to these errors. Postactivation potentiation resulted in a 40% gain in muscle contractility (p = .003), and there was a 26% increase in the neural stimulation of muscle (p = .014). Multiple regression indicated that the change in neural input had a stronger relationship with force errors than the increased contractility.