Reduced cortical voluntary activation during bilateral knee extension

IntroductionReduced neural drive is mainly thought to explain the bilateral deficit phenomenon, i.e. the difference in maximal isometric voluntary contraction (MVC) between unilateral and bilateral contractions. The aim of the present study was to further document if bilateral knee extension is associated with changes in voluntary activation level assessed by both peripheral nerve electrical stimulation and transcranial magnetic stimulation.MethodsFourteen subjects performed unilateral and bilateral knee extensions with both superimposed femoral electrical nerve stimulation and transcranial magnetic stimulation in order to assess voluntary activation (VA_FNES) and cortical voluntary activation (VA_TMS), respectively.ResultsThere was no difference in MVC force of the tested leg when involved in unilateral and bilateral knee extensions (p = 0.87). However, a significantly reduced VA_FNES (−2.1 ± 2.4%; p = 0.01) and VA_TMS (−1.6 ± 2.7%; p = 0.04) have been evidenced during bilateral knee extension.DiscussionIt is hypothesized that counterbalances could have masked the decrease of voluntary activation during bilateral contraction.     

The relationship between hip,knee and ankle muscle mechanical characteristics and gait transition speed

The purpose of the present study was to explore the relationship between mechanical characteristics of hip, knee and ankle extensor and flexor muscle groups and gait transition speed. The sample included 29 physically active male adults homogenized regarding their anthropometric dimensions. Isokinetic and isometric leg muscle mechanical characteristics were assessed by an isokinetic dynamometer, while individual walk-to-run (WRT) and run-to-walk transition speeds (RWT) were determined using the standard increment protocol. The relationship between transition speeds and mechanical variables scaled to body size was determined using Pearson correlation and stepwise linear regression. The highest correlations were found for isokinetic power of ankle dorsal flexors and WRT (r = .468, p < .01) and the power of hip extensors and RWT (r = .442, p < .05). These variables were also the best predictors of WRT and RWT revealing approximately 20% of explained variance. Under the isometric conditions, the maximal force and rate of force development of hip flexors and ankle plantar flexors were moderately related with WRT and RWT (ranged from r = .340 to .427). The only knee muscle mechanical variable that correlated with WRT was low velocity knee flexor torque (r = .366, p < .05). The results generally suggest that the muscle mechanical properties, such as the power of ankle dorsal flexors and hip extensors, influence values of WRT and RWT.     

How much does the human medial gastrocnemius muscle contribute to ankle torques outside the sagittal plane?

Ankle movements in the frontal plane are less prominent though not less relevant than movements in the plantar or dorsal flexion direction. Walking on uneven terrains and standing on narrow stances are examples of circumstances likely imposing marked demands on the ankle medio-lateral stabilization. Following our previous evidence associating lateral bodily sways in quiet standing to activation of the medial gastrocnemius (MG) muscle, in this study we ask: how large is the MG contribution to ankle torque in the frontal plane? By arranging stimulation electrodes in a selective configuration, current pulses were applied primarily to the MG nerve branch of ten subjects. The contribution of populations of MG motor units of progressively smaller recruitment threshold to ankle torque was evaluated by increasing the stimulation amplitude by fixed amounts. From smallest intensities (12–32 mA) leading to the firstly observable MG twitches in force-plate recordings, current pulses reached intensities (56–90 mA) below which twitches in other muscles could not be observed from the skin. Key results showed a substantial MG torque contribution tending to rotate upward the foot medial aspect (ankle inversion). Nerve stimulation further revealed a linear relationship between the peak torque of ankle plantar flexion and inversion, across participants (Pearson R > .81, p < .01). Specifically, regardless of the current intensity applied, the peak torque of ankle inversion amounted to about 13% of plantar flexion peak torque. Physiologically, these results provide experimental evidence that MG activation may contribute to stabilize the body in the frontal plane, especially under situations of challenged stability.     

Comparison of trunk muscle reflex activation patterns between active and passive trunk flexion–extension loading conditions

The aim of the present study was to determine the effects of trunk flexion–extension loading on the neuromuscular reflexive latencies and amplitude responses of the trunk musculature. Eighteen male and female subjects (18–27 yrs) participated in active and passive trunk flexion extension, performed ∼7 days apart. Subjects performed 60 trunk flexion–extension repetitions. Surface electromyography (EMG) was collected bilaterally from paraspinal and abdominal muscles. In the active condition, subjects volitionally moved their trunks, while in the passive condition the dynamometer controlled the movements. The trunk was perturbed before and immediately after 30 repetitions. Latency of muscle onset, latency of first peak, latency of maximum peak, and peak EMG amplitude were evaluated. No differences between conditions, sides, or perturbation session were apparent. Overall latencies were shorter in females (p < .05) and abdominal muscles compared to paraspinals (p < .05). Thoracic paraspinal muscle amplitudes were greater than all other muscles (p < .05). Based upon the present results, the neuromuscular system engages trunk flexor muscles prior to the paraspinals in order to provide possible stabilization of the trunk when flexor moments are generated. Overall, the results indicate no difference in response of the neuromuscular system to active or passive repetitive loading.     

The effect of swinging the arms on muscle activation and production of leg force during ski skating at different skiing speeds

The study investigated the effects of arm swing during leg push-off in V2-alternate/G4 skating on neuromuscular activation and force production by the leg muscles. Nine skilled cross-country skiers performed V2-alternate skating without poles at moderate, high, and maximal speeds, both with free (SWING) and restricted arm swing (NOSWING). Maximal speed was 5% greater in SWING (P < 0.01), while neuromuscular activation and produced forces did not differ between techniques. At both moderate and high speed the maximal (2% and 5%, respectively) and average (both 5%) vertical force and associated impulse (10% and 14%) were greater with SWING (all P < 0.05). At high speed range of motion and angular velocity of knee flexion were 24% greater with SWING (both P < 0.05), while average EMG of m. biceps femoris was 31% lower (all P < 0.05) in SWING. In a similar manner, the average EMG of m. vastus medialis and m. biceps femoris were lower (17% and 32%, P < 0.05) during the following knee extension. Thus, swinging the arms while performing V2-alternate can enhance both maximal speed and skiing economy at moderate and, in particularly, high speeds.     

Increased forefoot loading is associated with an increased plantar flexion moment

The aim of this study was to identify the cascade of effects leading from alterations in force generation around the ankle joint to increased plantar pressures under the forefoot. Gait analysis including plantar pressure measurement was performed at an individually preferred and a standardized, imposed gait velocity in diabetic subjects with polyneuropathy (n = 94), without polyneuropathy (n = 39) and healthy elderly (n = 19). The plantar flexion moment at 40% of the stance phase was negatively correlated with the displacement rate of center of pressure (r = ?.749, p < .001 at the imposed, and r = ?.693, p < .001 at the preferred gait velocity). Displacement rate of center of pressure was strongly correlated with forefoot loading (r = ?.837, p < .001 at the imposed, and r = ?.731, p < .001 at the preferred gait velocity). People with a relatively high plantar flexion moment at 40% of the stance phase, have a faster forward transfer of center of pressure and consequently higher loading of the forefoot. This indicates that interventions aimed at increasing the control of the roll-off of the foot may contribute to a better plantar pressure distribution.     

Similar changes in muscle fiber phenotype with differentiated consequences for rate of force development: Endurance versus resistance training

Resistance training has been shown to positively affect the rate of force development (RFD) whereas there is currently no data on the effect of endurance training on RFD. Subjects completed ten weeks of either resistance training (RT, n = 7) or endurance cycling (END, n = 7). Pre and post measurements included biopsies obtained from m. vastus lateralis to quantify fiber phenotype and fiber area and isokinetic dynamometer tests to quantify maximal torque (Nm) and RFD (Nm/s) at 0–30, 0–50, 0–100 and 0–200 ms during maximal isometric contraction for both knee extensors and flexors. Both groups increased the area percentage of type IIa fibers (p < .01) and decreased the area percentage of type IIx fibers (p = .05), whereas only RT increased fiber size (p < .05). RT significantly increased eccentric, concentric and isometric strength for both knee extensors and flexors, whereas END did not. RT increased 200 ms RFD (p < .01) in knee flexor RFD and a tendency towards an increase at 100 ms (p < .1), whereas tendencies towards decreases were observed for the END group at 30, 50 and 100 ms (p < .1), resulting in RT having a higher RFD than END at post (p < .01). In conclusion, resistance training may be very important for maintaining RFD, whereas endurance training may negatively impact RFD.     

H-reflex excitability is inhibited in soleus,but not gastrocnemius,at the short-latency response of a horizontal jump-landing task

Impaired spinal-level neuromuscular control is suggested to contribute to instability and injury during dynamic landing tasks. Despite this suggestion, spinal-level neuromuscular control is yet to be examined during a horizontal jump-landing task. The aim of the current study was to assess changes in H-reflexes and its reliability at the short-latency response of landings from short and long distances. Eight healthy individuals (five male, three female; age, 22 ± 1.2 yrs; height, 178 ± 8.1 cm; weight, 72 ± 15.7 kg) participated in the study. H-reflexes were evoked at the SLR in the soleus and medial gastrocnemius muscles, during two landing conditions: 25% and 50% of maximal broad jump distance. H-reflexes were expressed relative to the background electromyography (EMG) and maximal M-wave responses (M-max). Soleus H-reflexes were inhibited when landing from shorter distance (25%, 13.9 ± 7.6%; 50%, 8.3 ± 6.5%; p < 0.01). No change in H-reflex excitability was observed in medial gastrocnemius. Background EMG was unaltered across landing conditions. Inhibition of soleus H-reflex excitability from 25% to 50% landing condition indicates a reduced contribution of Ia-afferent feedback to the alpha-motor neuron during landings from greater distances, which may contribute to stiffness regulation at the ankle joint. Unaltered H-reflex excitability of medial gastrocnemius is most likely attributed to its functional role during the landing task.     

Local muscle oxygen consumption related to external and joint specific power

The purpose of the present study was to examine the effects of external work rate on joint specific power and the relationship between knee extension power and vastus lateralis muscle oxygen consumption (mVO₂). We measured kinematics and pedal forces and used inverse dynamics to calculate joint power for the hip, knee and ankle joints during an incremental cycling protocol performed by 21 recreational cyclists. Vastus lateralis mVO₂ was estimated using near-infrared spectroscopy with an arterial occlusion. The main finding was a non-linear relationship between vastus lateralis mVO₂ and external work rate that was characterised by an increase followed by a tendency for a levelling off (R² = 0.99 and 0.94 for the quadratic and linear models respectively, p < 0.05). When comparing 100 W and 225 W, there was a ∼43 W increase in knee extension but still a ∼9% decrease in relative contribution of knee extension to external work rate resulting from a ∼47 W increase in hip extension. When vastus lateralis mVO₂ was related to knee extension power, the relationship was still non-linear (R² = 0.99 and 0.97 for the quadratic and linear models respectively, p < 0.05). These results demonstrate a non-linear response in mVO₂ relative to a change in external work rate. Relating vastus lateralis mVO₂ to knee extension power showed a better fit to a linear equation compared to external work rate, but it is not a straight line.     

Frequency and pattern of voluntary pedalling is influenced after one week of heavy strength training

Changes in voluntary rhythmic leg movement characteristics of freely chosen cadence (reflecting movement frequency) and tangential pedal force profile (reflecting movement pattern) were investigated during 4 weeks of (i) heavy hip extension strength training (HET, n = 9), (ii) heavy hip flexion strength training (HFT, n = 9), and (iii) no intervention (CON, n = 9). Training consisted of three 5RM–10RM sets per session, with two sessions/week. Submaximal ergometer cycling was performed before the training period (pretest) and after every week of training (test A1, A2, A3, and posttest). Strength increased by on average 25% in HET and 33% in HFT. Freely chosen cadence was only changed in HET, occurring already after 1 week of training. Thus, percentage reductions of cadence in HET at test A1, A2, A3, and posttest, with respect to the pretest value, amounted for maximally on average 17%, or 14 rpm, and were larger than the corresponding changes in CON (p = .037). Percentage increases in minimum tangential pedal force in HET at test A1, A2, A3, and posttest, with respect to the pretest value, were larger than the corresponding changes in CON (p = .024). Heavy hip flexion strength training did not cause such alterations.     

Trunk coordination in healthy and chronic nonspecific low back pain subjects during repetitive flexion–extension tasks: Effects of movement asymmetry,velocity and load

Multiple joint interactions are critical to produce stable coordinated movements and can be influenced by low back pain and task conditions. Inter-segmental coordination pattern and variability were assessed in subjects with and without chronic nonspecific low back pain (CNSLBP). Kinematic data were collected from 22 CNSLBP and 22 healthy volunteers during repeated trunk flexion–extension in various conditions of symmetry, velocity, and loading; each at two levels. Sagittal plane angular data were time normalized and used to calculate continuous relative phase for each data point. Mean absolute relative phase (MARP) and deviation phase (DP) were derived to quantify lumbar–pelvis and pelvis–thigh coordination patterns and variability. Statistical analysis revealed more in-phase coordination pattern in CNSLBP (p = 0.005). There was less adaptation in the DP for the CNSLBP group, as shown by interactions of Group by Load (p = .008) and Group by Symmetry by Velocity (p = .03) for the DP of pelvis–thigh and lumbar–pelvis couplings, respectively. Asymmetric (p < 0.001) and loaded (p = 0.04) conditions caused less in-phase coordination. Coordination variability was higher during asymmetric and low velocity conditions (p < 0.001). In conclusion, coordination pattern and variability could be influenced by trunk flexion–extension conditions. CNSLBP subjects demonstrated less adaptability of movement pattern to the demands of the flexion–extension task.     

Neuromechanical synergies in single-leg landing reveal changes in movement control

Our purpose was to examine changes in single-leg landing biomechanics and movement control following alterations in mechanical task demands via external load and landing height. We examined lower-extremity kinematic, kinetic, and electromyographic (EMG) adjustments, as well as changes in movement control from neuromechanical synergies using separate principal component analyses (PCA). Nineteen healthy volunteers (15M, 4F, age: 24.3 ± 4.9 y, mass: 78.5 ± 14.7 kg, height: 1.73 ± 0.08 m) were analyzed among 9 single-leg drop landing trials in each of 6 experimental conditions (3 load and 2 landing height) computed as percentages of subject bodyweight (BW, BW + 12.5%, BW + 25%) and height (H12.5% & H25%). Condition order was counterbalanced, including: 1.) BW·H12.5, 2.) BW + 12.5·H12.5, 3.) BW + 25·H12.5, 4.) BW·H25, 5.) BW + 12.5·H25, 6.) BW + 25·H25. Lower-extremity sagittal joint angles and moments (hip, knee, & ankle), vertical ground reaction force (GRFz), and electrical muscle activity (gluteus maximus, biceps femoris, vastus medialis, medial gastrocnemius, & tibialis anterior muscles), were analyzed in each trial. Biomechanical adjustments and neuromechanical synergies were assessed using PCA. Subjects reduced effective landing height through segmental configuration adjustments at ground contact, extending at the hip and ankle joints with greater load and landing height (p ⩽ 0.028 and p ⩽ 0.013, respectively), while using greater medial gastrocnemius pre-activation with greater load (p ⩽ 0.006). Dimension reduction was observed under greater mechanical task demands, compressing and restructuring synergies among patterns of muscle activation, applied loads, and segmental configurations. These results provide insight into movement control and potential injury mechanisms in landing activities.     

Fatigue-induced dissociation between rate of force development and maximal force across repeated rapid contractions

We examined whether the presence of fatigue induced by prolonged running influenced the time courses of force generating capacities throughout a series of intermittent rapid contractions. Thirteen male amateur runners performed a set of 15 intermittent isometric rapid contractions of the knee extensor muscles, (3 s/5 s on/off) the day before (PRE) and immediately after (POST) a half marathon. The maximal voluntary contraction force, rate of force development (RFD_peak), and their ratio (relative RFD_peak) were calculated. At POST, considering the first (out of 15) repetition, the maximal force and RFD_peak decreased (p < 0.0001) at the same extent (by 22 ± 6% and 24 ± 22%, respectively), resulting in unchanged relative RFD_peak (p = 0.6). Conversely, the decline of RFD_peak throughout the repetitions was more pronounced at POST (p = 0.02), thus the decline of relative RFD_peak was more pronounced (p = 0.007) at POST (−25 ± 13%) than at PRE (−3 ± 13%). The main finding of this study was that the fatigue induced by a half-marathon caused a more pronounced impairment of rapid compared to maximal force in the subsequent intermittent protocol. Thus, the fatigue-induced impairment in rapid muscle contractions may have a greater effect on repeated, rather than on single, attempts of maximal force production.     

Selective activation of lower leg muscles during maximum voluntary isometric contractions

The pronators and supinators play a key role in the medio-lateral stability of the ankle joint complex (i.e. talo-crural and subtalar joints). We hypothesized that each shank muscle has a specific activation pattern determined by its anatomical course around the axes of the subtalar and talo-crural joints. A secondary objective was to examine the effect of foot posture on these activation patterns. Forty-nine young adults (25 normal-arched feet, 24 flat-arched feet) performed maximum voluntary isometric contractions against manual resistance in four movement directions: plantarflexion (PF), dorsiflexion (DF), pronation (PRO) and supination (SUP). Electromyographic activity was recorded from tibialis posterior (TP) and peroneus longus (PL) with intramuscular electrodes, and gastrocnemius medialis (GM) and tibialis anterior (TA) with surface electrodes. When compared to their agonist function, all muscles were co-activated at significantly lower levels in their synergistic function (GM: 23% during SUP, TA: 72% during SUP; TP: 42% during PF, PL: 52% during PF) (p < 0.001). A significant interaction between foot posture and contraction type was evident for TA. During isometric contractions, the electromyographic activity of the shank muscles is geared to their biomechanical advantage according to their position relative to the subtalar and talo-crural joint axes.     

Muscle force compensation among synergistic muscles after fatigue of a single muscle

PurposeThe aim of this study was to examine control strategies among synergistic muscles after fatigue of a single muscle. It was hypothesized that the compensating mechanism is specific for each fatigued muscle.MethodsThe soleus (SOL), gastrocnemius lateralis (GL) and medialis (GM) were fatigued in separate sessions on different days. In each experiment, subjects (n = 11) performed maximal voluntary contractions prior to and after fatiguing a single muscle (SOL, GL or GM) while the voluntary muscle activity and torque were measured. Additionally, the maximal single twitch torque of the plantarflexors and the maximal spinal reflex activity (H-reflex) of the SOL, GL and GM were determined. Fatigue was evoked using neuromuscular stimulation.ResultsFollowing fatigue the single twitch torque decreased by −20.1%, −19.5%, and −23.0% when the SOL, GL, or GM, have been fatigued. The maximal voluntary torque did not decrease in any session but the synergistic voluntary muscle activity increased significantly. Moreover, we found no alterations in spinal reflex activity.ConclusionsIt is concluded that synergistic muscles compensate each other. Furthermore, it seems that self-compensating mechanism of the fatigued muscles occurred additionally. The force compensation does not depend on the function of the fatigued muscle.     

Goal equivalent manifold analysis of task performance in non-specific LBP and healthy subjects during repetitive trunk movement: Effect of load,velocity, symmetry

Motor abundance allows reliability of motor performance despite its variability. The nature of this variability provides important information on the flexibility of control strategies. This feature of control may be affected by low back pain (LPB) and trunk flexion/extension conditions.Goal equivalent manifold (GEM) analysis was used to quantify the ability to exploit motor abundance during repeated trunk flexion/extension in healthy individuals and people with chronic non-specific LBP (CNSLBP).Kinematic data were collected from 22 healthy volunteers and 22 CNSLBP patients during metronomically timed, repeated trunk flexion/extension in three conditions of symmetry, velocity, and loading; each at two levels. A goal function for the task was defined as maintaining a constant movement time at each cycle. Given the GEM, flexibility index and performance index were calculated respectively as amounts of goal-equivalent variability and the ratio of goal-equivalent to non-goal-equivalent variability.CNSLBP group was as similar as healthy individuals in both flexibility index (p = 0.41) and performance index (p = 0.24). Performance index was higher in asymmetric (p < 0.001), high velocity (p < 0.001), and loaded (p = 0.006) conditions.Performance and flexibility in using motor abundance were influenced by repeated trunk flexion/extension conditions. However, these measures were not significantly affected by CNSLBP.     

Technique determinants of knee joint loads during cutting in female soccer players

The aim of this study was to investigate the relationships between technique characteristics and knee abduction moments during 90° cuts. A cross sectional design involving 26 elite and sub-elite female soccer players (mean ± SD; age: 21 ± 3.2 years, height: 1.68 ± 0.07 m, and mass: 59.1 ± 6.8 kg) was used to explore relationships between pre-determined technical factors on knee abduction moments during cutting. Three dimensional motion analyses of 90° cuts on the right leg were performed using ‘Qualisys Pro Reflex’ infrared cameras (240 Hz). Ground reaction forces were collected from two AMTI force platforms (1200 Hz) embedded into the running track to examine 2nd last and last footfalls. Pearson’s correlation coefficients, co-efficients of determination and hierarchical multiple regression were used to explore relationships between a range of technique parameters and peak knee abduction moments. Significance was set at p < .05. Hierarchical multiple regression revealed that initial knee abduction angle, lateral leg plant distance and initial lateral trunk lean could explain 67% (62% adjusted) of the variation in peak knee abduction moments (F_(1,22) = 8.869, p = .007). These findings reveal potential modifiable technical factors to lower peak knee abduction moments during cutting.     

Treadmill based reference running data for healthy subjects is dependent on speed and morphological parameters

ObjectiveTo obtain spatiotemporal and dynamic running parameters of healthy participants and to identify relationships between running parameters, speed, and physical characteristics.MethodA dynamometric treadmill was used to collect running data among 417 asymptomatic subjects during speeds ranging from 10 to 24 km/h. Spatiotemporal and dynamic running parameters were calculated and measured.ResultsResults of the analyses showed that assessing running parameters is dependent on running speed. Body height correlated with stride length (r = 0.5), cadence (r = −0.5) and plantar forefoot force (r = 0.6). Body mass also had a strong relationship to plantar forefoot forces at 14 and 24 km/h and plantar midfoot forces at 14 and 24 km/h.ConclusionThis reference data base can be used in the kinematic and kinetic evaluation of running under a wide range of speeds.     

Muscle strength and functional performance is markedly impaired at the recommended time point for sport return after anterior cruciate ligament reconstruction in recreational athletes

PurposeTo examine potential deficits in muscle strength or functional capacity when comparing (1) an ACL reconstructed group to matched healthy controls, (2) the ACL reconstructed leg to the non-injured leg and (3) the non-injured leg to matched healthy controls, at the time-point of recommended sport return 9–12 months post-surgery.MethodsSixteen patients (male-female ratio: 9:7) 9–12 months post ACL reconstruction and sixteen age and sex matched healthy controls were included. Outcome measures included maximal knee extensor (KE) and knee flexor (KF) dynamometry, including measurement of rate of force development, functional capacity (counter movement jump (CMJ) and single distance hop (SDH)) and the Lysholm score.ResultsCompared to the control group, maximal KE and KF muscle strength were impaired in the ACL reconstructed leg by 27–39% and 16–35%, respectively (p < .001). Also, impairments of both CMJ (38%) and SDH (33%) were observed (p < .001). Rate of force development for KE were reduced in the ACL group compared to the control group (p < .001). Similarly, the KE and KF muscle strength, CMJ and SDH of the ACL reconstructed leg were impaired, when compared to the non-injured leg by 15–23%, 8–20%, 23% and 20%, respectively (p < .05).ConclusionMuscle strength and functional capacity are markedly impaired in the ACL reconstructed leg of recreationally active people 9–12 months post-surgery when compared to healthy matched controls and to their non-injured leg. This suggests that objective criteria rather than “time-since-surgery” criteria should guide return to sport.     

Proprioceptive impairments associated with knee osteoarthritis are not generalized to the ankle and elbow joints

The mechanisms for proprioceptive changes associated with knee osteoarthritis (OA) remain elusive. Observations of proprioceptive changes in both affected knees and other joints imply more generalized mechanisms for proprioceptive impairment. However, evidence for a generalized effect remains controversial. This study examined whether joint repositioning proprioceptive deficits are localized to the diseased joint (knee) or generalized across other joints (elbow and ankle) in people with knee OA. Thirty individuals with right knee OA (17 female, 66 ± 7 [mean ± SD] years) of moderate/severe radiographic disease severity and 30 healthy asymptomatic controls of comparable age (17 female, 65 ± 8 years) performed active joint repositioning tests of the knee, ankle and elbow in randomised order in supine. Participants with knee OA had a larger relative error for joint repositioning of the knee than the controls (OA: 2.7 ± 2.1°, control: 1.6 ± 1.7°, p = .03). Relative error did not differ between groups for the ankle (OA: 2.2 ± 2.5°, control: 1.9 ± 1.3°, p = .50) or elbow (OA: 2.5 ± 3.3°, control: 2.9 ± 2.8°, p = .58). These results are consistent with a mechanism for proprioceptive change that is localized to the knee joint. This could be mediated by problems with mechanoreceptors, processing/relay of somatosensory input to higher centers, or joint-specific interference with cognitive processes by pain.