Comparison of postoperative clinical outcomes and knee stability of cruciate-retaining total knee arthroplasty using the tibia-first gap navigation technique with a computer-aided system and measured-resection technique: A retrospective analysis of a propensity-matched cohort.

Purpose: This study aimed to clarify whether the range of motion (ROM), anterior and posterior (AP) stability and other clinical measures changed in patients who underwent tibia-first total knee arthroplasty (TF-TKA) using navigation with a computer-aided system after surgery. Methods: This is a retrospective study and we conducted a matched cohort analysis of 60 measured resection (MR)-TKAs and 52 TF-TKAs performed by a single surgeon. All the surgeries used the same implant and approach. Baseline differences between the groups were adjusted using propensity score matching. We compared each patient's measured ROM and Oxford Knee Score (OKS) and performed knee AP laxity measurements by using a device during routine follow-ups. Results: A total of 40 MR-TKAs with a mean age of 73.5 ± 5.6 years and sex (male 10, female 30) were compared to 40 TF-TKAs with a mean age of 74.0 ± 5.7 years and sex (male 13, female 27) at 2-year follow-ups. Two years postoperatively, there was a significant difference in the AP laxity at 30° of knee flexion between both groups (7.0 ± 3.4 mm vs. 5.2 ± 2.3 mm, p < 0.01). In contrast, no differences were found between both groups for knee flexion (120.8 ± 9° vs. 116.7 ± 9.8°, p = 0.07) and OKS score (41.8 ± 6.9 vs. 41.0 ± 5.9, p = 0.61). Conclusion: The AP stability in the midflexion obtained using the tibia-first technique remained consistent even after 2 years. However, OKS and ROM were not significantly different from those of the MR-TKA group. Level of Evidence: Retrospective comparative LEVEL III study.

Use of a preoperative 3D templating and proximal lateral tibial fitting patient-specific instrumentation in fixed valgus complex primary total knee arthroplasty for a patient with retaining hardware for internal fixation to treat Schatzker type V tibial plateau fracture: A case report.

A 72-year-old female patient with a fixed valgus knee deformity due to a Schatzker type V tibial plateau fracture treated with bilateral locking plates 8 years ago was admitted to our clinic with complaints of chronic pain and knee instability when walking. Radiographs revealed Kellgren-Lawrence Classification grade 4 knee osteoarthritis and 20.5° of valgus knee deformity. She was treated with three-dimensional templating and proximal lateral tibial fitting patient-specific instrumentation-assisted mechanically aligned posterior sacrificing total knee arthroplasty with minimal removal of the retained hardware for the internal fixation of the tibial plateau fracture via a lateral approach, resulting in a favorable clinical outcome. The use of proximal lateral tibial fitting patient-specific instrumentation in fixed valgus complex primary total knee arthroplasty for patients with retaining hardware for internal fixation to treat tibial plateau fractures is considered a treatment option to decrease surgical invasion.

Effectiveness and Adherence Rate of S-flurbiprofen Plaster for the Pain Management of Patients With Moderate and End-Stage Knee Osteoarthritis.

BACKGROUND: S-flurbiprofen plaster (SFPP) is highly skin permeable and represents a new conservative treatment for knee osteoarthritis (KOA) that can attain considerably higher concentrations in the synovium than topical flurbiprofen. To date, no study has investigated the efficacy and adherence rate of SFPP in patients with end-stage KOA. This study aimed to compare the effectiveness and adherence rate of SFPP for pain management in patients with moderate and end-stage KOA. METHODS: This retrospective study included a total of 118 patients with KOA (Kellgren-Lawrence classification grades II (n = 29), III (n = 32), and IV (n = 57)). The difference in SFPP use rate, adverse drug reactions rate, whether 50% pain relief occurred, and the percentage of patients who underwent surgical treatment were calculated. RESULTS: The overall SFPP use rate at one year was 61.0% (88.1% at less than one month, 79.7% at three months, and 61.0% at six months), with no significant differences among Kellgren-Lawrence grade II, III, and IV groups (p = 0.538). Adverse drug reactions such as skin rash (n = 23), skin irritation (n = 8), and gastrointestinal disorders (n = 2) were observed. The one-year SFPP use rate was significantly lower in patients in whom these side effects occurred but did not decrease in patients in whom only a skin rash occurred. Overall, 19 patients underwent surgery after discontinuation of SFPP use. Surgery was statistically selected more by the "over 71 years of age" group (p = 0.038) and the "ineffective" group (p = 0.007). CONCLUSION: SFPP exerts a comparable therapeutic effect even in end-stage KOA and may be an effective treatment option. Even if patients have end-stage KOA, there are cases in which the patient's background does not allow for surgery positively, such as high perioperative risk or desire for conservative treatment. In such cases, SFPP may be an effective treatment option worth trying.

Effects of simulated trunk flexion contracture on the margin of stability during obstacle crossing in elderly individuals.

BACKGROUND: Trunk flexion contracture is an abnormal posture in elderly individuals with lumbar kyphosis. It is unclear whether this posture affects locomotor stability (margin of stability [MoS]) during obstacle crossing, which is a common trigger for falls in elderly people. RESEARCH QUESTION: Does trunk flexion contracture negatively affect MoS during obstacle crossing in elderly people? METHODS: Ten healthy elderly individuals performed five trials of obstacle crossing using a comfortable speed under two experimental conditions, namely, with (FLEX) or without (NORMAL) a hard lumbar brace to simulate trunk flexion contracture. The obstacle-crossing motion was captured using an optical motion analysis system in order to calculate the MoS in the anteroposterior direction. The MoS at initial contact (IC) and that when the swing foot was above the obstacle (Obs) was compared between FLEX and NORMAL. A greater MoS suggests greater risk of a forward fall. The trunk and lower limb joint angles were measured at Obs. RESULTS: FLEX significantly increased the MoS at IC, whereas the MoS at Obs did not differ between the two conditions. FLEX demonstrated a crouch posture characterized by an increased flexion angle of stance-side hip and knee joints at the Obs instant. SIGNIFICANCE: Forward fall chance might be increased at IC in obstacle crossing with trunk flexion contracture. Meanwhile, the MoS at Obs might be controlled by increasing the crouch posture to offset a forward shift in the CoM position due to the trunk flexion. Because the risk of a stumble on an obstacle and of forward falls should be higher at Obs than at IC, the crouch posture seems to be an effective adaptation that enables elderly people with trunk flexion contracture to safely cross obstacles.

Habitual patellar dislocation 40 years after failed conservative treatment: A case report.

Patellar dislocation is often caused by congenital bone morphological abnormalities or joint laxity and is rarely traumatic. We report a case of long-term habitual patellar dislocation due to trauma 40 years ago without abnormal bone morphology, which required a combined procedure, including the Elmslie-Trillat (ET) procedure, massive lateral release, and medial patellofemoral ligament (MPFL) reconstruction, resulting in favorable outcomes. A 52-year-old male, with no specific underlying disease, dislocated his right patella due to falls when he was 13 years old and underwent conservative treatment. Subsequently, patellofemoral instability remained, and the patella began dislocating outward every time he flexed his knee joint; however, he could walk without pain. Therefore, he left it untreated for more than 40 years. His Lysholm and Kujala scores were 77 and 73 points, respectively. Radiographs showed no abnormal bone morphology with a tibial tuberosity-tibial groove (TT-TG) distance of 12 mm and a tibial external rotation angle of 5°. We released the distal iliotibial ligament and lateral bursa following the Fulkerson procedure, and the patella was stabilized from 0° to 60° of knee flexion. The ET procedure was subsequently performed. The patella was moved 13 mm medially and fixed using tibial coarse translation, which stabilized the patella up to 90°. However, when flexed beyond 90°, the patella was displaced laterally; therefore, MPFL reconstruction with autologous hamstring tendon was performed. Range of motion exercises were initiated 1 day postoperatively. Partial and full weight-bearing were allowed 2 and 4 weeks postoperatively, respectively. At the final outpatient follow-up at 8 months postoperatively, the patient could walk without patellofemoral instability; the Lysholm and Kujala scores had recovered from 77 to 97 and from 73 to 93 points, respectively. This combined patellofemoral-stabilizing procedure is considered the treatment of choice for patients with habitual patellar dislocation despite the chronicity.

Valgus knee deformity due to nonunion of lateral Hoffa fracture: A case report.

Hoffa fractures are rare intra-articular injuries, and nonunion of Hoffa fractures is rarer. We report the case of an adult male with a nonunion of a Hoffa fracture by open reduction and internal fixation in which the lateral meniscus tear was treated by an arthroscopic surgery. A healthy 38-year-old man who had a history of untreated trauma to the left knee in a motorcycle accident 11 years ago presented to our hospital with the complaint of chronic left knee pain for 5 years. The patient had an obvious valgus knee with 0°-140° of motion, and radiographs revealed the nonunion of the left lateral Hoffa fracture (Letenneur type-III). Routine arthroscopic evaluation and a lateral meniscus posterior tear repair using all inside device were performed. The knee joint was exposed using a lateral para patella approach. The fracture was fixed with three 4.5-mm headless screws and distal femoral locking plates. Mobilization was started from the first operative day. Full weight bearing was allowed 8 weeks postoperatively. At the 1-year follow up, the X-ray showed healing of the nonunion site with no displacement of the Hoffa fracture. The knee range of motion, lower limb alignment, and clinical outcome were also improved. Nonunion of the Hoffa fracture should be treated by an internal fixation despite the chronicity.

Kinetic and Kinematic Analyses of Countermovement Jump in a Small Sample of Individuals with Congenital Vision Loss.

In the present study, we aimed to explore whether countermovement jumps (CMJs) performed by young adults with and without visual impairment (VI) differ. We compared three participants with congenital VI to 10 participants without congenital VI when both groups performed CMJs with maximum effort. Although the maximum jump height did not differ between groups, all three participants with VI showed such reduced maximum downward velocity of the center of body mass and a relative net negative vertical impulse that, on these measures, they fell beyond two standard deviations from the mean scores of participants without VI. The range of motion for the leg joints and countermovement depth did not differ between groups. Although findings from our small sample should be cross-validated and trainers should take care to protect athletes from falls, it appears from our preliminary data that a path to improved CMJ performance for athletes with VI is to increase their movement velocity in the countermovement phase of the jump.

Addition of 3D-CT evaluation to radiographic images and effect on diagnostic reliability of current 2018 AO/OTA classification of femoral trochanteric fractures.

INTRODUCTION: The AO/OTA classification for diagnosing femoral trochanteric fractures (31A fractures) was revised in 2018. No studies have investigated whether the addition of CT to radiographic diagnosis improves the inter-rater reliability of classifying 31A fractures with the current AO/OTA criteria. The study aimed to test the hypothesis that the addition of three-dimensional CT (3D-CT) to radiographic diagnosis would improve diagnostic reliability. METHODS: A retrospective review was conducted to assess the diagnostic reliability of classification of 31A fractures with current AO/OTA criteria. Radiographs and 3D-CT images from 89 cases were assessed. Major fracture types (A1, A2, and A3) and subgroups were diagnosed by nine orthopedic surgeons who were classified into three groups (high-, intermediate-, and low-experience) according to their clinical experience. Anterior-posterior and lateral radiographs were provided to diagnose fracture type (first assessment). After a 6-week interval, radiographs and 3D-CT images of all cases were evaluated by each rater (second assessment). Fleiss's Kappa was used to determine inter-rater reliability. RESULTS: In the first assessment, the Kappa value indicated fair inter-rater reliability in all groups (high-experience group: κ = 0.296, 95% confidence interval [CI] 0.239-0.352; intermediate-experience group: κ = 0.367, 95% CI 0.305-0.428; low-experience group: κ = 0.304, 95% CI 0.246-0.362). With the addition of 3D-CT (second assessment), reliability improved from fair to moderate in the high- and intermediate-experience groups (κ = 0.483, 95% CI 0.428-0.539 and κ = 0.409, 95% CI 0.352-0.466, respectively). By contrast, reliability remained fair in the low-experience group (κ = 0.322, 95% CI 0.322-0.431). The inter-rater reliability of diagnosing subgroup fracture types improved for A2.3 and A3.1 in all three groups and for A3.2 and A3.3 in the intermediate- and low-experience groups. CONCLUSION: The current AO/OTA classification revised in 2018 provided fair reliability in diagnosing femoral trochanteric fractures in all three surgeon groups. The addition of 3D-CT to radiographic image evaluation improved reliability in high- and middle-expertise groups. The addition of 3D-CT to radiographic evaluation often improved the diagnostic reliability for unstable fractures, although there was some variation among fracture subgroups.

Sound design for auditory biofeedback and motor performance in participants with stroke: a pilot study.

Background: Although auditory biofeedback (ABF) has proved to be effective in stroke rehabilitation, there are a variety of means by which to present information through sound. Objectives: To examine if ABF sound design influences the motor performance of patients with stroke. Methods: A total of four people with chronic stroke participated . They were asked to track target signals by their paretic ankle dorsiflexion. Half of the participants were assigned to one of the two groups. Those in the Error ABF group heard ABF that alerted them to the error between the target and the joint angle. Those in the Full ABF group heard ABF that presented both the target and the angle separately by modulating the frequencies of two sounds. Therefore, when there was no error, no sound or two sounds with the identical frequency were heard in the Error and Full ABF sessions, respectively. The same visual BF (VBF) was always present regardless of the group. The accuracy of the task was quantified via an accuracy index (AI, ranging from -100 to 100). All participants were trained by repeating tracking, and the pre- and post-training AIs were obtained. Results: The AIs of all participants increased after training, but the increase was greater for the Error ABF group (mean increase = 8.9 and 14.9 for the Full and Error groups, respectively). Conclusions: The Full ABF was less effective than the Error ABF, probably because the VBF was present, and the information provided by the Full ABF was therefore redundant.

The degree of postural automaticity influences the prime movement and the anticipatory postural adjustments during standing in healthy young individuals.

Less attention to a balance task reduces the center of foot pressure (COP) variability by automating the task. However, it is not fully understood how the degree of postural automaticity influences the voluntary movement and anticipatory postural adjustments. Eleven healthy young adults performed a bipedal, eyes closed standing task under the three conditions: Control (C, standing task), Single (S, standing + reaction tasks), and Dual (D, standing  +  reaction + mental tasks). The reaction task was flexing the right shoulder to an auditory stimulus, which causes counter-clockwise rotational torque, and the mental task was arithmetic task. The COP variance before the reaction task was reduced in the D condition compared to that in the C and S conditions. On average the onsets of the arm movement and the vertical torque (Tz, anticipatory clockwise rotational torque) were both delayed, and the maximal Tz slope (the rate at which the torque develops) became less steep in the D condition compared to those in the S condition. When these data in the D condition were expressed as a percentage of those in the S condition, the arm movement onset and the Tz slope were positively and negatively, respectively, correlated with the COP variance. By using the mental-task induced COP variance reduction as the indicator of postural automaticity, our data suggest that the balance task for those with more COP variance reduction is less cognitively demanding, leading to the shorter reaction time probably due to the attention shift from the automated balance task to the reaction task.

Comparative Effects of Auditory Electromyographic Biofeedback for Participants Who Are Blind and Sighted.

This study examined differences in auditory electromyographic biofeedback (AEB) effects between participants who were sighted and blind. Past research makes clear that AEB is effective for people who are blind, particularly because of their reported superiority in auditory processing, but no study has directly compared AEB efficacy between participants who are sighted and blind. A total of 11 participants who were sighted and 10 who were blind performed a motor task requiring 20 nonfatiguing muscle contractions at 20% maximal voluntary contraction (MVC) with or without AEB. AEB reduced the error (calculated as the absolute difference of two consecutive contractions) among both participant groups, and the error for the group without biofeedback was greater for the participants who were blind than that for the sighted participants (5.20% ± 2.05% MVC and 3.30% ± 1.26% MVC, respectively; p < .05). This finding was consistent with subjective rating data, also indicating a trend toward greater difficulty for participants who were blind when performing without biofeedback. Moreover, the AEB/no biofeedback condition showed fewer errors for the participants who were blind than for the participants who were sighted during the last part of the task ( p = .036), indicating that participants who were blind were better at maintaining the AEB effect. These data suggest that the poor motor performance of participants who were blind was greatly improved with AEB, suggesting important applications of AEB for assistive technologies, adapted sports, and activities of daily living.

Erratum to: Reduced health-related quality of life among Japanese college students with visual impairment.

[This corrects the article DOI: 10.1186/s13030-015-0045-1.].

Heat stress and cardiovascular, hormonal, and heat shock proteins in humans.

CONTEXT: Conditions such as osteoarthritis, obesity, and spinal cord injury limit the ability of patients to exercise, preventing them from experiencing many well-documented physiologic stressors. Recent evidence indicates that some of these stressors might derive from exercise-induced body temperature increases. OBJECTIVE: To determine whether whole-body heat stress without exercise triggers cardiovascular, hormonal, and extracellular protein responses of exercise. DESIGN: Randomized controlled trial. SETTING: University research laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-five young, healthy adults (13 men, 12 women; age = 22.1 ± 2.4 years, height = 175.2 ± 11.6 cm, mass = 69.4 ± 14.8 kg, body mass index = 22.6 ± 4.0) volunteered. INTERVENTION(S): Participants sat in a heat stress chamber with heat (73°C) and without heat (26°C) stress for 30 minutes on separate days. We obtained blood samples from a subset of 13 participants (7 men, 6 women) before and after exposure to heat stress. MAIN OUTCOME MEASURE(S): Extracellular heat shock protein (HSP72) and catecholamine plasma concentration, heart rate, blood pressure, and heat perception. RESULTS: After 30 minutes of heat stress, body temperature measured via rectal sensor increased by 0.8°C. Heart rate increased linearly to 131.4 ± 22.4 beats per minute (F6,24 = 186, P < .001) and systolic and diastolic blood pressure decreased by 16 mm Hg (F6,24 = 10.1, P < .001) and 5 mm Hg (F6,24 = 5.4, P < .001), respectively. Norepinephrine (F1,12 = 12.1, P = .004) and prolactin (F1,12 = 30.2, P < .001) increased in the plasma (58% and 285%, respectively) (P < .05). The HSP72 (F1,12 = 44.7, P < .001) level increased with heat stress by 48.7% ± 53.9%. No cardiovascular or blood variables showed changes during the control trials (quiet sitting in the heat chamber with no heat stress), resulting in differences between heat and control trials. CONCLUSIONS: We found that whole-body heat stress triggers some of the physiologic responses observed with exercise. Future studies are necessary to investigate whether carefully prescribed heat stress constitutes a method to augment or supplement exercise.

Dynamic-position-sense impairment's independence of perceived knee function in women with ACL reconstruction.

CONTEXT: There is conflicting evidence in the literature regarding whether women with anterior cruciate ligament reconstruction (ACLR) demonstrate impaired proprioception. This study examined dynamic-position-sense accuracy and central-nervous-system (CNS) processing time between those with and without long-term ACLR. OBJECTIVE: To compare proprioception of knee movement in women with ACLR and healthy controls. DESIGN: Cross-sectional. SETTING: Human neuromuscular performance laboratory. PARTICIPANTS: 11 women (age 22.64 ± 2.4 y) with ACLR (1.6-5.8 y postsurgery) and 20 women without (age 24.05 ± 1.4 y). INTERVENTIONS: The authors evaluated subjects using 3 methods to assess position sense. During knee flexion at pseudorandomly selected speeds (40°, 60°, 80°, 90°, and 100°/s), subjects indicated with their index finger when their knee reached a predetermined target angle (50°). Accuracy was calculated as an error score. CNS processing time was computed using the time to detect movement and the minimum time of angle indication. Passive and active joint-position sense were also determined at a slow velocity (3°/s) from various knee-joint starting angles. MAIN OUTCOME MEASUREMENTS: Absolute and constant error of target angle, indication accuracy, CNS processing time, and perceived function. RESULTS: Both subject groups showed similar levels of error during dynamic-position-sense testing, despite continued differences in perceived knee function. Estimated CNS processing time was 260 ms for both groups. Joint-position sense during slow active or passive movement did not differ between cohorts. CONCLUSIONS: Control and ACLR subjects demonstrated similar dynamic, passive, and active joint-position-sense error and CNS processing speed even though ACLR subjects reported greater impairment of function. The impairment of proprioception is independent of post-ACLR perception of function.

Cortical and segmental excitability during fatiguing contractions of the soleus muscle in humans.

OBJECTIVE: The aim of this study was to examine the cortical and segmental excitability changes during fatigue of the soleus muscle. METHODS: Ten healthy young subjects performed 45 plantar flexion maximal voluntary contractions (MVCs) (7-s on/3-s off) in 9 epochs of five contractions. Motor evoked potentials (MEPs) using transcranial magnetic stimulation and H-reflexes were assessed during the task. RESULTS: The torque and the soleus EMG activity both showed the greatest decline during the 1st epoch, followed by a gradual, but significant decrease by the end of the task (∼70% pre-fatigue). The H-reflex sampled at rest after each epoch decreased to 66.6±18.3% pre-fatigue after the first epoch, and then showed no further change. The MEP on 10% pre-fatigue MVC after each epoch increased progressively (252.9±124.2% pre-fatigue). There was no change in the MEPs on the 3rd MVC in each epoch. The silent period on the MVC increased (109.0±9.2% pre-fatigue) early with no further changes during the task. CONCLUSIONS: These findings support that the motor cortex increases excitability during fatigue, but with a concomitant inhibition. SIGNIFICANCE: These findings are in contrast to upper extremity muscles and may reflect a distinct response specific to postural, fatigue-resistant muscle.

Prior heat stress effects fatigue recovery of the elbow flexor muscles.

INTRODUCTION: Long-lasting alterations in hormones, neurotransmitters, and stress proteins after hyperthermia may be responsible for the impairment in motor performance during muscle fatigue. METHODS: Subjects (n = 25) performed a maximal intermittent fatigue task of elbow flexion after sitting in either 73° or 26°C to examine the effects of prior heat stress on fatigue mechanisms. RESULTS: The heat stress increased the tympanic and rectal temperatures by 2.3° and 0.82°C, respectively, but there was full recovery prior to the fatigue task. Although prior heat stress had no effects on fatigue-related changes in volitional torque, electromyographic (EMG) activity, torque relaxation rate, motor evoked potential (MEP) size, and silent period (SP) duration, prior heat stress acutely increased the pre-fatigue relaxation rate and chronically prevented long-duration fatigue (P < 0.05). CONCLUSIONS: These findings indicate that prior passive heat stress alone does not alter voluntary activation during fatigue, but prior heat stress and exercise produce longer-term protection against long-duration fatigue.

Quadriceps low-frequency fatigue and muscle pain are contraction-type-dependent.

Eccentric contractions are thought to induce greater low-frequency fatigue (LFF) and delayed-onset muscle soreness (DOMS) than concentric contractions. In this study we induced a similar amount of eccentric quadriceps muscle fatigue during either a concentric or eccentric fatigue task to compare LFF and DOMS. Subjects (n = 22) performed concentric or eccentric fatigue tasks using 75% of the pre-fatigue maximal voluntary contraction (MVC) torque, and both tasks ended when the MVC eccentric torque decreased by 25% pre-fatigue. When subjects reached the failure criterion during the eccentric and concentric tasks, the concentric MVC was 78 +/- 9.8% and 64 +/- 8.4% of initial, respectively. LFF was greater after the concentric than the eccentric protocols (22 +/- 12.4% and 15 +/- 7.6% increase, respectively; P < 0.01). DOMS was over 100% greater for the eccentric protocol. These results indicate that DOMS is not dependent on the events that contribute to LFF.

Repetitive eccentric muscle contractions increase torque unsteadiness in the human triceps brachii.

Torque steadiness and low-frequency fatigue (LFF) were examined in the human triceps brachii after concentric or eccentric fatigue protocols. Healthy young males (n=17) performed either concentric or eccentric elbow extensor contractions until the eccentric maximal voluntary torque decreased to 75% of pre-fatigue for both (concentric and eccentric) protocols. The number of concentric contractions was greater than the number of eccentric contractions needed to induce the same 25% decrease in eccentric MVC torque (52.2+/-2.9 vs. 41.5+/-2.1 for the concentric and eccentric protocols, respectively, p<.01). The extent of peripheral fatigue was approximately 12% greater after the concentric compared to the eccentric protocol (twitch amplitude), whereas LFF (increase in double pulse torque/single pulse torque), was similar across protocols. Steadiness, or the ability for a subject to hold a submaximal isometric contraction, was approximately 20 % more impaired during the Ecc protocol (p=.052). Similarly, the EMG activity required to hold the torque steady was nearly 20% greater after the eccentric compared to concentric protocol. These findings support that task dependent eccentric contractions preferentially alter CNS control during a precision based steadiness task.

Doublet stimulation protocol to minimize musculoskeletal stress during paralyzed quadriceps muscle testing.

With long-term electrical stimulation training, paralyzed muscle can serve as an effective load delivery agent for the skeletal system. Muscle adaptations to training, however, will almost certainly outstrip bone adaptations, exposing participants in training protocols to an elevated risk for fracture. Assessing the physiological properties of the chronically paralyzed quadriceps may transmit unacceptably high shear forces to the osteoporotic distal femur. We devised a two-pulse doublet strategy to measure quadriceps physiological properties while minimizing the peak muscle force. The purposes of the study were 1) to determine the repeatability of the doublet stimulation protocol, and 2) to compare this protocol among individuals with and without spinal cord injury (SCI). Eight individuals with SCI and four individuals without SCI underwent testing. The doublet force-frequency relationship shifted to the left after SCI, likely reflecting enhancements in the twitch-to-tetanus ratio known to exist in paralyzed muscle. Posttetanic potentiation occurred to a greater degree in subjects with SCI (20%) than in non-SCI subjects (7%). Potentiation of contractile rate occurred in both subject groups (14% and 23% for SCI and non-SCI, respectively). Normalized contractile speed (rate of force rise, rate of force fall) reflected well-known adaptations of paralyzed muscle toward a fast fatigable muscle. The doublet stimulation strategy provided repeatable and sensitive measurements of muscle force and speed properties that revealed meaningful differences between subjects with and without SCI. Doublet stimulation may offer a unique way to test muscle physiological parameters of the quadriceps in subjects with uncertain musculoskeletal integrity.

Low frequency fatigue in human quadriceps is fatigue dependent and not task dependent.

It is well accepted that a low intensity/long duration isometric contraction induces more low frequency fatigue (LFF) compared to a high-intensity/short-duration contraction. However, previous reports examined the intensity/duration of the contraction but did not control the level of fatigue when concluding fatigue is task dependent. The purpose of this study was to determine whether a long duration/low intensity fatiguing contraction would induce greater LFF than a short duration/high-intensity contraction when the quadriceps muscle was fatigued to similar levels. Eighteen healthy male subjects performed quadriceps contractions sustained at 35% and 65% of maximal voluntary contraction (MVC) on separate days, until the tasks induced a similar amount of fatigue (force generating capacity=45% MVC). Double pulse torque to single pulse torque ratio (D/S ratio) was obtained before, immediately and 5min after fatigue along with the electromyographic (EMG) signal from vastus medialis (VM) and rectus femoris (RF). The D/S ratio significantly (p<0.05) increased by 8.7+/-8.5% (mean+/-SD) and 10.2+/-9.2% after 35% and 65% tasks, respectively, and remained elevated 5min into recovery; however, there was no significant difference in ratio between the two sessions immediately or 5min post-fatigue (p>0.05) even though the endurance time for the 35% fatigue task (124+/-39.68s) was significantly longer (p=0.05) than that of the 65% task (63+/-17.73s). EMG amplitude and median power frequency (MPF) analysis also did not reveal any significant differences between these two sessions after fatigue. These findings indicate that LFF fatigue is fatigue dependent as well as task intensity/duration dependent. These findings assist us in understanding task dependency and muscle fatigue.