Are unilateral and bilateral knee osteoarthritis patients unique subsets of knee osteoarthritis? A biomechanical perspective.

OBJECTIVE: To compare the gait of adults with unilateral and bilateral symptomatic and radiographic knee osteoarthritis (OA) to determine whether these subgroups can be treated similarly in the clinic and when recruiting for randomized clinical trials, and to use these data to generate future hypotheses regarding gait in these subsets of knee OA patients. METHODS: Cross-sectional investigation of patients with unilateral and bilateral knee OA on gait mechanics using 136 older adults (age ≥55 yrs; 27 kg m(-2) ≥ BMI ≤ 41 kg m(-2); 82% female) with radiographic knee OA. Comparisons were made between the most affected side of the bilateral group (Bi) and the affected side of the unilateral group (Uni), and between symmetry indices of each group. RESULTS: There were no significant differences in any temporal, kinematic, or kinetic measures between the Uni and Bi cohorts. Comparison of symmetry indices between groups also revealed no significant differences. CONCLUSION: The similarity in lower extremity mechanics between unilateral and bilateral knee OA patients is sufficiently robust to consider both subsets as a single cohort. We hypothesize that biomechanical adaptations to knee OA are at least partially systemic in origin and not based solely on the physiological characteristics of an affected knee joint.

The Intensive Diet and Exercise for Arthritis (IDEA) trial: 18-month radiographic and MRI outcomes.

PURPOSE: Report the radiographic and magnetic resonance imaging (MRI) structural outcomes of an 18-month study of diet-induced weight loss, with or without exercise, compared to exercise alone in older, overweight and obese adults with symptomatic knee osteoarthritis (OA). METHODS: Prospective, single-blind, randomized controlled trial that enrolled 454 overweight and obese (body mass index, BMI = 27-41 kg m(-2)) older (age ≥ 55 yrs) adults with knee pain and radiographic evidence of femorotibial OA. Participants were randomized to one of three 18-month interventions: diet-induced weight loss only (D); diet-induced weight loss plus exercise (D + E); or exercise-only control (E). X-rays (N = 325) and MRIs (N = 105) were acquired at baseline and 18 months follow-up. X-ray and MRI (cartilage thickness and semi-quantitative (SQ)) results were analyzed to compare change between groups at 18-month follow-up using analysis of covariance (ANCOVA) adjusted for baseline values, baseline BMI, and gender. RESULTS: Mean baseline descriptive characteristics of the cohort included: age, 65.6 yrs; BMI 33.6 kg m(-2); 72% female; 81% white. There was no significant difference between groups in joint space width (JSW) loss; D -0.07 (SE 0.22) mm, D + E -0.27 (SE 0.22) mm and E -0.16 (SE 0.24) mm (P = 0.79). There was also no significant difference in MRI cartilage loss between groups; D -0.10(0.05) mm, D + E -0.13(0.04) mm and E -0.05(0.04) mm (P = 0.42). CONCLUSION: Despite the potent effects of weight loss in this study on symptoms as well as mechanistic outcomes (such as joint compressive force and markers of inflammation), there was no statistically significant difference between the three active interventions on the rate of structural progression either on X-ray or MRI over 18-months.

Influences of alignment and obesity on knee joint loading in osteoarthritic gait.

OBJECTIVE: To determine the influences of frontal plane knee alignment and obesity on knee joint loads in older, overweight and obese adults with knee osteoarthritis (OA). METHODS: Cross-sectional investigation of alignment and obesity on knee joint loads using community dwelling older adults (age ≥ 55 years; 27 kg m(-2) ≥ body mass or body mass index (BMI) ≤ 41 kg m(-2); 69% female) with radiographic knee OA that were a subset of participants (157 out of 454) enrolled in the Intensive Diet and Exercise for Arthritis (IDEA) clinical trial. RESULTS: A higher BMI was associated with greater (P = 0.0006) peak knee compressive forces [overweight, 2411 N (2182, 2639), class 1 obesity, 2772 N (2602, 2943), class 2+ obesity, 2993 N (2796, 3190)] and greater (P = 0.004) shear forces [overweight, 369 N (322, 415), class 1 obesity, 418 N (384, 453), class 2+ obesity, 472 N (432, 513)], independent of alignment, and varus alignment was associated (P < 0.0001) with greater peak external knee adduction moments, independent of BMI [valgus, 18.7 Nm (15.1, 22.4), neutral, 27.7 Nm (24.0, 31.4), varus, 37.0 Nm (34.4, 39.7)]. CONCLUSION: BMI and alignment were associated with different joint loading measures; alignment was more closely associated with the asymmetry or imbalance of loads across the medial and lateral knee compartments as reflected by the frontal plane external adduction moment, while BMI was associated with the magnitude of total tibiofemoral force. These data may be useful in selecting treatment options for knee OA patients (e.g., diet to reduce compressive loads or bracing to change alignment).

Effects of real and sham whole-body mechanical vibration on spinal excitability at rest and during muscle contraction.

We examined the effects of whole-body mechanical vibration (WBV) on indices of motoneuronal excitability at rest and during muscle contraction in healthy humans. Real and sham WBV at 30 Hz had no effect on reflexes measured during muscle contraction. Real WBV at 30 and 50 Hz depressed the H-reflex ∼45%. These depressions diminished across the five inter-bout rest intervals. The depression converted to 27% and 7% facilitation over the 15-min long recovery period following real WBV at 30 and 50 Hz, respectively. The depression, measured during the inter-bout rest, correlated r = 0.48 (P = 0.007) with the subsequent facilitation, measured during the follow-up. The depression produced by sham vs real WBV was significant but less (23%), recovered faster, and the facilitation was absent in the 15-min long follow-up period. WBV produced time-varying depression followed by facilitation of the H-reflex at rest. A lack of change in volitional wave suggests that WBV did not affect the efferent neural drive.

The biomechanical mechanism of how strength and power training improves walking speed in old adults remains unknown.

Maintaining and increasing walking speed in old age is clinically important because this activity of daily living predicts functional and clinical state. We reviewed evidence for the biomechanical mechanisms of how strength and power training increase gait speed in old adults. A systematic search yielded only four studies that reported changes in selected gait biomechanical variables after an intervention. A secondary analysis of 20 studies revealed an association of r(2)=0.21 between the 22% and 12% increase, respectively, in quadriceps strength and gait velocity in 815 individuals age 72. In 6 studies, there was a correlation of r(2)=0.16 between the 19% and 9% gains in plantarflexion strength and gait speed in 240 old volunteers age 75. In 8 studies, there was zero association between the 35% and 13% gains in leg mechanical power and gait speed in 150 old adults age 73. To increase the efficacy of intervention studies designed to improve gait speed and other critical mobility functions in old adults, there is a need for a paradigm shift from conventional (clinical) outcome assessments to more sophisticated biomechanical analyses that examine joint kinematics, kinetics, energetics, muscle-tendon function, and musculoskeletal modeling before and after interventions.

Does high weight loss in older adults with knee osteoarthritis affect bone-on-bone joint loads and muscle forces during walking?

OBJECTIVE: The aim of this study was to examine the effects of high weight loss on knee joint loads during walking in participants with knee osteoarthritis (OA). DESIGN: Data were obtained from a subset of participants enrolled in the Arthritis, Diet, and Activity Promotion Trial (ADAPT). Complete baseline and 18-month follow-up data were obtained on 76 sedentary, overweight or obese older adults with radiographic knee OA. Three-dimensional gait analysis was used to calculate knee joint forces and moments. The cohort was divided into high (>5%), low (<5%), and no (0% or gain) weight loss groups. RESULTS: From baseline body weight, the high weight loss group lost an average of 10.2%, the low weight loss group lost an average of 2.7%, and the no weight loss group gained 1.5%. Adjusted 18-month outcome data revealed lower maximum knee compressive forces with greater weight loss (P=0.05). The difference in compressive forces between the high weight loss and no weight loss groups was due primarily to lower hamstring forces (P=0.04). Quadriceps forces were similar between the groups at 18-month follow-up. There was no difference between the groups in 18-month joint space width or Kellgren-Lawrence scores. CONCLUSIONS: These results suggest that a 10% weight loss in an overweight and obese osteoarthritic population elicits positive changes in the mechanical pathway to knee OA by having lower knee joint compressive loads during walking compared to low and no weight loss groups. The difference in compressive forces was due, in large part, to reductions in hamstring co-contraction during the initial portion of the stance phase.

Effects of standard and eccentric overload strength training in young women.

PURPOSE: According to the force-velocity relationship of human skeletal muscle, the maximal load one can lift is limited by the concentric movement phase, and the eccentric phase is always underloaded. In the present study, we hypothesized that acute exercise training using an eccentric overload compared with standard loading would lead to greater neuromuscular and strength adaptations. METHODS: Sedentary women (age 20.9 yr) were tested for concentric and eccentric three-repetition maximum (3RM), maximal isokinetic eccentric and concentric and isometric force and associated EMG activity of selected thigh muscles before and after 7 consecutive days of exercise training of the left quadriceps. The exercise program was designed so that the total weight lifted was similar between the eccentric overload (EO, N = 10) and standard group (ST, N = 10), but EO exercised with about 50% greater eccentric load whereas the controls did not exercise (N = 10). RESULTS: There was a 22% increase in the total weight lifted over 7 d. On the average, EOs compared with STs strength gains were approximately twofold greater. Changes in EMG paralleled the changes in muscle strength without changes in biceps femoris coactivity during knee extension. CONCLUSION: Because the strength gains were achieved by exercising at low intensities and over a short time period, exercise prescription of eccentric overloading appears especially suitable for elders, individuals deconditioned due to an injury, and the chronically diseased.

Relationship between fat-to-fat-free mass ratio and decrements in leg strength after downhill running.

The purpose of this study was to determine whether greater body fat mass (FM) relative to lean mass would result in more severe muscle damage and greater decrements in leg strength after downhill running. The relationship between the FM-to-fat-free mass ratio (FM/FFM) and the strength decline resulting from downhill running (-11% grade) was investigated in 24 male runners [age 23.4 +/- 0.7 (SE) yr]. The runners were divided into two groups on the basis of FM/FFM: low fat (FM/FFM = 0.100 +/- 0.008, body mass = 68.4 +/- 1.3 kg) and normal fat (FM/FFM = 0.233 +/- 0.020, body mass = 76.5 +/- 3.3 kg, P < 0.05). Leg strength was reduced less in the low-fat (-0.7 +/- 1.3%) than in the normal-fat individuals (-10.3 +/- 1.5%) 48 h after, compared with before, downhill running (P < 0.01). Multiple linear regression analysis revealed that the decline in strength could be predicted best by FM/FFM (r2 = 0.44, P < 0.05) and FM-to-thigh lean tissue cross-sectional area ratio (r2 = 0.53, P < 0.05), with no additional variables enhancing the prediction equation. There were no differences in muscle glycogen, creatine phosphate, ATP, or total creatine 48 h after, compared with before, downhill running; however, the change in muscle glycogen after downhill running was associated with a higher FM/FFM (r = -0.56, P < 0.05). These data suggest that FM/FFM is a major determinant of losses in muscle strength after downhill running.

Low- or high-intensity strength training partially restores impaired quadriceps force accuracy and steadiness in aged adults.

Because many daily tasks are executed at only a fraction of maximal strength, an understanding of submaximal force control may be important for improving function in aged adults. We compared the effects of low- and high-intensity (LI and HI, respectively) strength training on maximal and explosive strength and on the accuracy (force error) and steadiness (variability) of submaximal quadriceps force in elderly humans. Older subjects (age, 72 years; n = 27) had 57% lower maximal strength in comparison with young subjects (age, 21 years; n = 10). Older subjects had 190% (19 N), 50% (1 N), and 80% (4 N) more force error in matching 25 N of quadriceps force during eccentric, isometric, and concentric contractions, and had 157%, 0%, and 60% more variability in these forces compared with young subjects. Force error and force variability were correlated with each other but not with maximal strength. Thirty sessions of LI (n = 9 participants) or HI (n = 9 participants) training of equal total work increased maximal strength in the older subjects by 29%. Training also significantly reduced force error and variability--by 31% and 30%, respectively--of eccentric and concentric contractions. A control group of older subjects (n = 9) showed no significant changes in any variables. LI or HI strength training was equally effective in partially restoring elderly adults' maximal strength and control of submaximal force.

Age increases the skeletal versus muscular component of lower extremity stiffness during stepping down.

Elderly adults step down with greater lower extremity stiffness than young adults. The purpose of this study was to compare skeletal and muscular components of lower extremity stiffness between elderly and young adults during stepping down. Fourteen elderly (age, 70.1 years) and 16 young (age, 20.8 years) adults stepped down onto a force plate from 10% and 20% body heights while being videotaped. Lower extremity stiffness was defined as the ratio between the floor reaction force directed along the limb and limb compression. It was partitioned into skeletal and muscular components using the angular relationship (phi) between the direction of the force and the line of the leg. Our results showed that phi was 21% smaller (p < .03), the skeletal component was 48% larger (p < .025), and the ratio of skeletal to muscular components was 32% larger (p < .01) in elderly adults compared with young adults. Elderly adults rely more on their skeletal and less on their muscular systems when stepping down compared with young adults, producing a stiffer lower extremity.

Favorable neuromuscular and cardiovascular responses to 7 days of exercise with an eccentric overload in elderly women.

The metabolic, cardiovascular, and neural cost of eccentric muscle contraction is less than that of concentric contraction, but the strength and neural adaptations in eccentric contractions are significantly greater following resistive exercise. We thus compared the short-term effects of exercise with an eccentric overload (n = 10) with those of exercise with a standard load distribution (n = 10) in ostensibly healthy sedentary elderly women (mean age 71.4). Subjects were tested for concentric and eccentric three-repetition maximum, maximal isokinetic eccentric and concentric and isometric force, and associated electromyographic activity of selected thigh muscles before and after 7 consecutive days of exercise training of the left knee extensors. The exercise program was designed so that the total weight lifted was similar between eccentric overload and standard groups, but the eccentric overload group exercised with an approximately 50% greater eccentric load. Control subjects did not exercise (n = 10). There was a 46% increase in the total weight lifted over 7 days. When all strength measures were combined, the eccentric overload group's strength gains were 1.8-fold greater than those of the standard group, and the cardiovascular stress in terms of heart rate, mean arterial pressure, rate pressure product, and perceived exertion was significantly lower. The increases in muscle strength were achieved by increased muscle activation, but the strength gains were independent of the changes in antagonistic muscle coactivity. Because the strength gains occurred after a short period of exercise at a relatively low intensity and cardiovascular demand, the prescription of exercise with an eccentric overload appears suitable for elders, individuals deconditioned as a result of an injury, and the chronically diseased.

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.

Muscle pre- and coactivity during downward stepping are associated with leg stiffness in aging.

We have previously reported that elderly compared to young women executed downward stepping with substantially greater leg stiffness. Because antagonist muscle coactivity increases joint stiffness we hypothesized that increased leg stiffness in aging is associated with increased muscle coactivity. We also explored the possibility that the magnitude of the preparatory muscle activity preceding impact also differed between young and old subjects. Young (n=11, 20. 8 yr) and old (n=12, 69 yr) women performed downward stepping from a platform set at 20% body height. The leg was modeled as a simple mass-spring system. From video and ground reaction force data leg stiffness was computed as the ratio of force under the foot and the linear shortening of the limb. EMG activity of the vastus lateralis, biceps femoris, gastrocnemius lateralis, and tibialis anterior were recorded with a telemetric system. Elders compared to young subjects had 64% greater leg stiffness during downward stepping. Muscle activity over a 200-ms period preceding touch down was 136% greater in elderly than in young subjects. Biceps femoris and tibialis anterior coactivity during ground contact was 120% greater in the elders. Muscle pre- and coactivity, respectively, accounted for about 50% of the variance in leg stiffness. In conclusion, elderly people elevate muscle pre- and coactivity during downward stepping to stiffen the leg in compensation for impaired neuromotor functions.

Foot placement modifies kinematics and kinetics during drop jumping.

PURPOSE: Sprinting, bouncing, and spontaneous landings are associated with a forefoot contact whereas walking, running, and jumping are associated with heel-toe foot placement. Because such foot placement strategies influence landing mechanics or the ensuing performance, the purpose of this work was to compare lower extremity kinematics and kinetics and muscle activation patterns between drop vertical jumps performed with heel-toe (HTL) and forefoot (FFL) landings. METHODS: Ten healthy male university students performed two types of drop jump from a 0.4-m high box placed 1.0-m from the center of the force plate. They were instructed to either land first on the ball of the feet without the heels touching the ground during the subsequent vertical jump, i.e., forefoot landing jump (FFL), or to land on the heels followed by depression of the metatarsals, i.e., heel-toe landing jump (HTL). Three successfully performed trials per jump type were included in the analysis. The criteria for selection of the correct jumps was proper foot position at contact as judged from video records and the shape of force-time curve. RESULTS: The first peak and second peak determined from the vertical force-time curves were 3.4 times greater and 1.4 times lower for HTL compared with those with FFL (P<0.05). In the flexion phase of HTL, the hip and knee joints contributed 40% and 45% to the total torque, whereas during FFL the greatest torque contributions were 37% for both the knee and ankle joints. During the extension phase, the greatest torque contributions to the total torque were 41% and 45% by the knee and ankle joints during HTL and 34% and 55% during FFL. During the flexion phase, power production was 20% greater (P<0.05) in HTL than in FFL, whereas during the extension phase power production was 40% greater in FFL than in HTL. In the flexion phase of HTL the hip and knee joints produced the greatest power, and during the extension phase the knee and ankle joints produced the greatest power. In contrast, during both the flexion and extension phases of FFL, the knee and ankle joints produced the greatest power. The EMG activity of gluteus, vastus lateralis, and plantar flexor muscles was similar between HTL and FFL in most cases except for the greater vastus lateralis EMG activity during precontact phase in HTL than in FFL and the greater gastrocnemius activity in FFL than in HTL. CONCLUSION: Foot placement strategy modifies the individual joint contributions to the total power during drop jumping.

Altered movement strategy increases lower extremity stiffness during stepping down in the aged.

One way the human neuromuscular system negotiates locomotory challenges is by stiffening the muscles and joints of a limb. Because aging reduces joint range of motion and muscle strength, the intrinsic elements of stiffness, we hypothesized that lower extremity stiffness would be greater in elderly than in young subjects during downward stepping. Fourteen elderly (mean age 70.1) and 16 young women (mean age 20.8) stepped down from a platform adjusted to 10% and 20% of body height. Subjects stepped down onto a force plate and were videotaped from the side. The lower extremity was modeled as a simple spring and stiffness was computed as the quotient of stress under the foot and the shortening of the limb. Ankle and knee joint angular position and velocity were also determined during stepping. Compared with young women, elders had 50% greater lower extremity stiffness and 28% less linear shortening of the limb. Elders also performed downward stepping with 92% less dorsiflexion and 28% less knee flexion and 42% less ankle and 57% less knee joint range of motion. Elders executed downward stepping with a more erect lower extremity alignment, resulting in a stiffer leg and an apparently safer movement strategy.

Functional knee brace effects during walking in patients with anterior cruciate ligament reconstruction.

The purpose of this study was to compare lower extremity joint kinematics and kinetics during walking with and without a functional knee brace in patients with recent anterior cruciate ligament reconstructions. Seven volunteers walked at 1.26 m/s with and without one of two functional knee braces 3 weeks after surgery. Eleven uninjured subjects were also tested as a control group. Video and ground-reaction data were collected and combined with inverse dynamics to estimate the joint positions, moments, and powers during the stance phase. Patients with ligament reconstructions were more erect with the brace, using 19% less knee flexion compared with walking without the brace. Areas under the internal extensor moment curve (angular impulse) and power curve (work) at the hip increased 40% and 44%, respectively, while walking with the brace. Extensor angular impulse decreased 41% at the knee while using the brace, and plantar flexor angular impulse and work increased 21% and 30%, respectively, at the ankle. While walking with the brace, the patients still had different kinematics, moments, and powers than the control subjects. The reduced extensor moment at the knee in the braced condition indicated that the load on the recently reconstructed ligament was reduced and that the brace protected the ligament during the stance phase of walking. We concluded that functional knee braces may be one means of developing neuromuscular adaptations during gait after anterior cruciate ligament reconstruction surgery.

Gait biomechanics are not normal after anterior cruciate ligament reconstruction and accelerated rehabilitation.

PURPOSE: Accelerated rehabilitation for anterior cruciate ligament (ACL) injury and reconstruction surgery is designed to return injured people to athletic activities in approximately 6 months. The small amount of empirical data on this population suggests, however, that the torque at the knee joint may not return until 22 months after surgery during walking and even longer during running. Although the rehabilitation has ended and individuals have returned to preinjury activities, gait mechanics appear to be abnormal at the end of accelerated programs. The purpose of this study was to compare lower extremity joint kinematics, kinetics, and energetics between individuals having undergone ACL reconstruction and accelerated rehabilitation and healthy individuals. METHODS: Eight ACL-injured and 22 healthy subjects were tested. Injured subjects were tested 3 wk and 6 months (the end of rehabilitation) after surgery. Ground reaction force and kinematic data were combined with inverse dynamics to predict sagittal plane joint torques and powers from which angular impulse and work were derived. RESULTS: The difference in all kinematic variables between the two tests for the ACL group averaged 38% (all P < 0.05). The kinematics were not different between the ACL group after rehabilitation and healthy subjects. Angular impulses and work averaged 100% difference for all joints (all P < 0.05) between tests for the ACL group. After rehabilitation, the differences between injured and healthy groups in angular impulse and work at both the hip and knee remained large and averaged 52% (all P < 0.05). CONCLUSIONS: Results indicated that after reconstruction surgery and accelerated rehabilitation for ACL injury, humans walk with normal kinematic patterns but continue to use altered joint torque and power patterns.

Gait adaptations before and after anterior cruciate ligament reconstruction surgery.

Gait analyses of rehabilitated individuals with anterior cruciate ligament (ACL) deficiency and reconstruction have identified the final adaptations of increased hip extensor torque and hamstring electromyography (EMG) and decreased knee extensor torque and quadriceps EMG during stance. The initial adaptations to injury and surgery are, however, unknown as are the factors that influence the development of the adaptations. Identification of the initial response to injury would provide a basis for determining whether the final adaptations are learned automatically or if they are the result of a lengthy training period in which various factors may affect their development. The purpose of the study was to evaluate the initial effects of ACL injury and reconstruction surgery on joint kinematics, kinetics, and energetics, during walking. Injured limbs from nine subjects with ACL injury were tested 2 wk after injury, and 3 and 5 wk after surgery. Ten healthy subjects were tested. Kinematic and ground reaction data were collected and combined with inverse dynamics to calculate the joint torques and powers. A knee extensor torque throughout most of stance was observed in the injured limbs at all test sessions. This result was in conflict with previous observations of reduced extensor torque or a flexor torque in rehabilitated patients with ACL reconstruction and patients with ACL deficiency. This result also differed from the typical midstance extensor then flexor torque in healthy control subjects. Trend analysis showed a significant (P < 0.001) change in average position at the hip and knee, extensor angular impulse at the hip, and positive work done at the hip 3 wk after surgery followed by a partial rehabilitation at 5 wk after surgery. Power and work produced at the knee were reduced fivefold (P < 0.001) after 5 wk of rehabilitation and did not recover to pre-surgical levels. The existence of a long-lasting knee extensor torque 2 wk after injury indicated that the adaptation process to ACL deficiency is lengthy, requiring many gait cycles, and that numerous factors could be involved in learning the adaptations.

Greater initial adaptations to submaximal muscle lengthening than maximal shortening.

The purpose of this study was to compare the short-term strength and neural adaptations to eccentric and concentric training at equal force levels. Forty-two sedentary women (age = 21.5 yr) were ranked based on the initial quadriceps strength score, and trios of subjects were randomly assigned to either an eccentric (n = 14), a concentric (n = 14), or a nonexercising control group (n = 14). Training involved a total of 824 eccentric or concentric quadriceps actions at 1.05 rad.s-1 administered in four sets of 6-10 repetitions, four times per week for 6 wk. Before and after training, all subjects were tested for unilateral maximal isometric and eccentric and concentric actions at 1.05 rad.s-1 and for a 40-repetition eccentric and concentric fatigue series of the left and right quadriceps. Surface electromyographic activity of the vastus lateralis and medialis was monitored during testing. Concentric training increased concentric (36%, P < 0.05), isometric (18%, P < 0.05), and eccentric strength (13%), and eccentric training increased eccentric (42%, P < 0.05), isometric (30%, P < 0.05), and concentric (13%) strength. Eccentric training improved eccentric and isometric strength more (P < 0.05) than did concentric training. The electromyographic adaptations were greater with eccentric training. Cross-education was 6%, and neither training mode modified fatigability. The data suggest that training of the quadriceps muscle with submaximal eccentric actions brings about greater strength adaptations faster than does training with maximal-level concentric actions in women. This greater adaptation is likely to be mediated by both mechanical and neural factors.

A functional knee brace alters joint torque and power patterns during walking and running.

Individuals with anterior cruciate ligament (ACL) injury use greater extensor torques at the hip and ankle and lower extensor torques and joint power at the knee during gait compared to healthy subjects. These adaptations may be mediated by (1) altered neuromuscular strategies due to the injury, (2) training effects produced by rehabilitation protocols, and (3) training effects due to the functional knee brace (FKB) used during rehabilitation. The purpose of the study was to test the hypothesis that a FKB can cause individuals to walk and run with the torque and power patterns observed in rehabilitated ACL-injured individuals. Ten healthy subjects were tested walking and running with and without a FKB. Kinematic and ground reaction data were collected and combined with inverse dynamics to estimate the joint torques and powers. Data were analyzed with a two-way repeated measures ANOVA (gait vs knee condition). In walking, the hip and ankle extensor torques were 14.3% (p < 0.038) and 5.1% (p < 0.003) greater with FKB. In running, the hip extensor torque was 17.0% greater with FKB (p < 0.023). Knee torque was not different between conditions. In walking, the work performed at the hip and knee were 11.6% greater (p < 0.013) and 17.7% lower with FKB (p < 0.025), respectively. Results supported the hypothesis and it was concluded that a FKB may be one causative factor in the development of the unique joint torque and power patterns seen in ACL-injured gait.