Jennifer E. Stevens

Quadriceps strength and volitional activation before and after total knee arthroplasty for osteoarthritis.

Introduction: Patients with osteoarthritis (OA) of the knee have quadriceps weakness and arthrogenous muscle inhibition (AMI). While total knee arthroplasty (TKA) reliably reduces pain and improves function in patients with knee OA, quadriceps weakness persists after surgery. The purpose of this investigation was to assess contributions of AMI to quadriceps weakness before and after TKA and to assess the effect of pain on AMI.

Early Quadriceps Strength Loss After Total Knee Arthroplasty: The Contributions of Muscle Atrophy and Failure of Voluntary Muscle Activation

BACKGROUND While total knee arthroplasty reduces pain and provides a functional range of motion of the knee, quadriceps weakness and reduced functional capacity typically are still present one year after surgery. The purpose of the present investigation was to determine the role of failure of voluntary muscle activation and muscle atrophy in the early loss of quadriceps strength after surgery. METHODS Twenty patients with unilateral knee osteoarthritis were tested an average of ten days before and twenty-seven days after primary total knee arthroplasty. Quadriceps strength and voluntary muscle activation were measured with use of a burst-superimposition technique in which a supramaximal burst of electrical stimulation is superimposed on a maximum voluntary isometric contraction. Maximal quadriceps cross-sectional area was assessed with use of magnetic resonance imaging. RESULTS Postoperatively, quadriceps strength was decreased by 62%, voluntary activation was decreased by 17%, and maximal cross-sectional area was decreased by 10% in comparison with the preoperative values; these differences were significant (p < 0.01). Collectively, failure of voluntary muscle activation and atrophy explained 85% of the loss of quadriceps strength (p < 0.001). Multiple linear regression analysis revealed that failure of voluntary activation contributed nearly twice as much as atrophy did to the loss of quadriceps strength. The severity of knee pain with muscle contraction did not change significantly compared with the preoperative level (p = 0.31). Changes in knee pain during strength-testing did not account for a significant amount of the change in voluntary activation (p = 0.14). CONCLUSIONS Patients who are managed with total knee arthroplasty have profound impairment of quadriceps strength one month after surgery. This impairment is predominantly due to failure of voluntary muscle activation, and it is also influenced, to a lesser degree, by muscle atrophy. Knee pain with muscle contraction played a surprisingly small role in the reduction of muscle activation.

Improved function from progressive strengthening interventions after total knee arthroplasty: A randomized clinical trial with an imbedded prospective cohort

OBJECTIVE To determine the effectiveness of progressive quadriceps strengthening with or without neuromuscular electrical stimulation (NMES) on quadriceps strength, activation, and functional recovery after total knee arthroplasty (TKA), and to compare progressive strengthening with conventional rehabilitation. METHODS A randomized controlled trial was conducted between July 2000 and November 2005 in an academic outpatient physical therapy clinic. Two hundred patients who had undergone primary, unilateral TKA for knee osteoarthritis were randomized to 1 of 2 interventions 4 weeks after surgery, and 41 patients eligible for enrollment who did not participate in the intervention were tested 12 months after surgery (standard of care group). All randomized patients received 6 weeks of outpatient physical therapy 2 or 3 times per week through 1 of 2 intervention protocols: an exercise group (volitional strength training) or an exercise-NMES group (volitional strength training and NMES). Treatment effects were evaluated by a burst superimposition test to assess quadriceps strength and volitional activation 3 and 12 months postoperatively. The Medical Outcomes Study Short Form 36 and Knee Outcome Survey were completed. Knee range of motion, Timed Up and Go, Stair-Climbing Test, and 6-Minute Walk were also measured. RESULTS Strength, activation, and function were similar between the exercise and exercise-NMES groups at 3 and 12 months. The standard of care group was weaker and exhibited worse function at 12 months compared with both treatment groups. CONCLUSION Progressive quadriceps strengthening with or without NMES enhances clinical improvement after TKA, achieving similar short- and long-term functional recovery and approaching the functional level of healthy older adults. Conventional rehabilitation does not yield similar outcomes.

Resistance training improves strength and functional capacity in persons with multiple sclerosis

The purpose of this study was to evaluate the effect of an eight-week progressive resistance training programme on lower extremity strength, ambulatory function, fatigue and self-reported disability in multiple sclerosis (MS) patients (mean disability score 3.79-0.8). Eight MS subjects volunteered for twice weekly training sessions. During the first two weeks, subjects completed one set of 8 -10 reps at 50% of maximal voluntary contraction (MVC) of knee flexion, knee extension and plantarflexion exercises. In subsequent sessions, the subjects completed one set of 10 -15 repetitions at 70% of MVC. The resistance was increased by 2 -5% when subjects completed 15 repetitions in consecutive sessions. Isometric strength of the quadriceps, hamstring, plantarflexor and dorsiflexor muscle groups was assessed before and after the training programme using an isokinetic dynamometer. Magnetic resonance images of the thigh were acquired before and after the exercise programme as were walking speed (25-ft), number of steps in 3 min, and self-reported fatigue and disability. Knee extension (7.4%), plantarflexion (52%) and stepping performance (8.7%) increased significantly (PB-0.05). Self-reported fatigue decreased (PB-0.05) and disability tended to decrease (P -0.07) following the training programme. MS patients are capable of making positive adaptations to resistance training that are associated with improved ambulation and decreased fatigue.

Are voluntary muscle activation deficits in older adults meaningful

The relationship between the central activation ratio (CAR) and contraction force is curvilinear, not linear as was previously believed. Voluntary quadriceps femoris muscle activation from previously collected data sets in 46 older adults (64–84 years) and 46 young adults (18–32 years) were therefore reexamined using a curvilinear model of the voluntary muscle activation–percent maximum voluntary force relationship. This method revealed lower voluntary muscle activation in older adults (0.868 ± 0.018) than younger subjects (0.978 ± 0.005). The mean difference between older and younger adults was 11%, which may be more meaningful than previous reports of 2–4% because it could explain the greater rate of strength loss as compared to loss of muscle mass as humans age. Muscle Nerve 27: 99–101, 2003

Lower extremity skeletal muscle function in persons with incomplete spinal cord injury

Study design:A cross-sectional study design.Objectives:To characterize and specifically quantify impairments in muscle function after chronic incomplete spinal cord injury (SCI).Setting:University of Florida, Gainesville, FL, USA.Methods:Voluntary and electrically elicited contractile measurements were performed and voluntary activation deficits were quantitatively determined in the knee extensor and ankle plantar flexor muscle groups in 10 individuals with chronic incomplete SCI (C5-T8, ASIA C or D) and age-, gender-, height- and body weight matched healthy controls.Results:Persons with incomplete-SCI were able to produce only 36 and 24% of the knee extensor torque and 38 and 26% of the plantar flexor torque generated by noninjured controls in the self-reported less-involved and more-involved limbs, respectively (P<0.05). In addition, both indices of explosive or instantaneous muscle strength, torque200 (absolute torque reached at 200 ms) and the average rate of torque development (ARTD) were dramatically reduced in the ankle plantar flexor and knee extensor muscle groups in persons with incomplete-SCI. However, the deficit in instantaneous muscle strength was most pronounced in the ankle plantar flexor muscles, with an 11.7-fold difference between the torque200 measured in the self-reported more involved limb and a 5-fold difference in the less-involved limb compared to control muscles. Voluntary activation deficits ranged between 42 and 66% in both muscle groups. Interestingly, electrically elicited contractile properties did not differ between the groups.Conclusion:The resultant impact of incomplete-SCI is that affected muscles not only become weak, but slow to develop voluntary torque. We speculate that the large deficit in torque200 and ARTD in the ankle plantar flexors muscles of persons with incomplete-SCI may limit locomotor function. The results presented in this study provide a quantitative and sensitive assessment of muscle function upon which future research examining rehabilitation programs aimed at restoring muscle function and promoting functional recovery after incomplete-SCI may be based.

Locomotor Training and Muscle Function After Incomplete Spinal Cord Injury: Case Series

Abstract Background/Objective: To determine whether 9 weeks of locomotor training (LT) results in changes in muscle strength and alterations in muscle size and activation after chronic incomplete spinal cord injury (SCI). Study Design: Longitudinal prospective case series. Methods: Five individuals with chronic incomplete SCI completed 9 weeks of LT. Peak isometric torque, torque developed within the initial 200 milliseconds of contraction (Torque200), average rate of torque development (ARTD), and voluntary activation deficits were determined using isokinetic dynamometry for the knee-extensor (KE) and plantar-flexor (PF) muscle groups before and after LT. Maximum muscle crosssectional area (CSA) was measured prior to and after LT. Results: Locomotor training resulted in improved peak torque production in all participants, with the largest increases in the more-involved PF (43.9% ± 20.0%), followed by the more-involved KE (21.1% ± 12.3%). Even larger improvements were realized in Torque200 and ARTD (indices of explosive torque), after LT. In particular, the largest improvements were realized in the Torque200 measures of the PF muscle group. Improvements in torque production were associated with enhanced voluntary activation in both the KE and ankle PF muscles and an increase in the maximal CSA of the ankle PF muscles. Conclusion: Nine weeks of LT resulted in positive alterations in the KE and PF muscle groups that included an increase in muscle size, improved voluntary activation, and an improved ability to generate both peak and explosive torque about the knee and ankle joints.

Non-invasive assessment of lower extremity muscle composition after incomplete spinal cord injury

Study Design:Cross-sectional study.Objective:(1) To quantify intramyocellular lipid (IMCL) content of the soleus muscle. (2) To assess the T2 relaxation rates in the lower extremity skeletal muscles in persons with incomplete spinal cord injury (SCI).Setting:Academic Institution, Florida.Methods:Eight subjects (42±10 years old; 70±12 kg; 176±10 cm) with chronic (17±9 months post injury) motor SCI (C4-T12; ASIA C or D) and eight matched healthy controls were tested. Localized unsuppressed proton spectroscopy (H-MRS) was performed to estimate total lipid content and individual lipid components; IMCL and extramyocellular lipid (EMCL) from the soleus muscle. T2-weighted imaging of lower extremity muscles yielded muscle T2 rates.Results:The IMCL content of the soleus muscle was 3.3 times higher in the patient group as compared to controls (P=0.002; 0.0401 (0.0234–0.0849) versus 0.0123 (0.0090–0.0175)). Similarly, EMCL measures were 4.5 times higher as compared to the controls (P=0.002). Significant differences were observed in the T2 relaxation times of the soleus and gastrocnemius muscles (P<0.05).Conclusion:The increased levels of IMCL might interfere with the glucose uptake in skeletal muscle; potentially predisposing persons with incomplete SCI to the development of peripheral insulin resistance. Marked elevations in the T2 relaxation times of the locomotor muscles are reflective of an altered muscle composition.