Chronic eccentric arm cycling improves maximum upper-body strength and power.

INTRODUCTION: Eccentric leg cycling (cycle ergometry adapted to impose muscle lengthening contractions) offers an effective exercise for restoring lower-body muscular function, maintaining health, and improving performance in clinical and athletic populations. PURPOSE: We extended this model to the upper body and evaluated the effectiveness of a 7-week eccentric arm cycling (ECCarm) intervention to improve upper-body muscular function. We also explored whether ECCarm would alter arterial function. METHODS: Participants performed ECCarm (n = 9) or concentric arm cycling (CONarm; n = 8) 3×/week while training intensity increased (5-20 min, 60-70% upper-body peak heart rate). Maximum elbow extensor strength, upper-body concentric power, and peripheral and central arterial stiffness were assessed before and after training. RESULTS: During training, heart rates and perceived exertion did not differ between groups (~68% upper-body peak heart rate, ~12 Borg units, both P > 0.05), whereas power during ECCarm was ~2× that for CONarm (122 ± 43 vs. 59 ± 20 W, P < 0.01). Muscle soreness for ECCarm was greater than CONarm (P = 0.02), however, soreness was minimal for both groups (<0.50 cm). Following training, ECCarm exhibited greater changes in elbow extensor strength (16 ± 10 vs. 1 ± 9%, P = 0.01) and upper-body power (6 ± 8 vs. -3 ± 7%, P < 0.01) compared to CONarm. Peripheral and central arterial stiffness did not change for either group (both P > 0.05). CONCLUSION: Upper-body eccentric exercise improved dynamic muscular function while training at low exertion levels. Results occurred with minimal soreness and without compromising arterial function. ECCarm findings parallel eccentric leg cycling findings and indicate that eccentric cycle ergometry offers a robust model for enhancing upper-body muscular function. ECCarm could have applications in rehabilitation and sport training.

Age-related differences in lean mass, protein synthesis and skeletal muscle markers of proteolysis after bed rest and exercise rehabilitation.

Bed rest-induced muscle loss and impaired muscle recovery may contribute to age-related sarcopenia. It is unknown if there are age-related differences in muscle mass and muscle anabolic and catabolic responses to bed rest. A secondary objective was to determine if rehabilitation could reverse bed rest responses. Nine older and fourteen young adults participated in a 5-day bed rest challenge (BED REST). This was followed by 8 weeks of high intensity resistance exercise (REHAB). Leg lean mass (via dual-energy X-ray absorptiometry; DXA) and strength were determined. Muscle biopsies were collected during a constant stable isotope infusion in the postabsorptive state and after essential amino acid (EAA) ingestion on three occasions: before (PRE), after bed rest and after rehabilitation. Samples were assessed for protein synthesis, mTORC1 signalling, REDD1/2 expression and molecular markers related to muscle proteolysis (MURF1, MAFBX, AMPKα, LC3II/I, Beclin1). We found that leg lean mass and strength decreased in older but not younger adults after bedrest (P < 0.05) and was restored after rehabilitation. EAA-induced mTORC1 signalling and protein synthesis increased before bed rest in both age groups (P < 0.05). Although both groups had blunted mTORC1 signalling, increased REDD2 and MURF1 mRNA after bedrest, only older adults had reduced EAA-induced protein synthesis rates and increased MAFBX mRNA, p-AMPKα and the LC3II/I ratio (P < 0.05). We conclude that older adults are more susceptible than young persons to muscle loss after short-term bed rest. This may be partially explained by a combined suppression of protein synthesis and a marginal increase in proteolytic markers. Finally, rehabilitation restored bed rest-induced deficits in lean mass and strength in older adults.

Exercise and medication effects on persons with Parkinson disease across the domains of disability: a randomized clinical trial.

BACKGROUND AND PURPOSE: Hypokinesia and bradykinesia as movement deficits of Parkinson disease are thought to be mediated by both basal ganglia dysfunction and a loss of muscle mass and strength commensurate with aging and decreased levels of physical activity. For these reasons, we sought to utilize resistance training as a means to increase muscle force and minimize hypokinesia and bradykinesia in persons with Parkinson disease and examine the effects of exercise and medication on Body Structure and Function (muscle force production and muscle cross-sectional area), Activity (mobility), and Participation (Health Status) outcomes. METHODS: Forty-two participants were enrolled in a 12-week randomized clinical trial that compared 2 active exercise interventions: a standard care control group (Active Control) and an experimental group that underwent Resistance Exercise via Negative Eccentric Work (RENEW). RESULTS: Participants in both groups improved in muscle force production and mobility as a result of exercise and medication (P < 0.02). There were no significant interaction or between-group differences and no significant changes in muscle cross-sectional area or health status were observed. Effect sizes for exercise and medication combined exceeded the effect sizes of either intervention in isolation. DISCUSSION AND CONCLUSIONS: Taken together, these results point to the complementary effects of exercise and medication on the Body Structure and Function and Activity outcomes but little effect on Participation outcomes.Video Abstract available for more insights from the authors (see Supplemental Digital Content 1, http://links.lww.com/JNPT/A92).

Low Physical Function in Maintenance Hemodialysis Patients Is Independent of Muscle Mass and Comorbidity.

OBJECTIVES: It is unknown whether muscle wasting accounts for impaired physical function in adults on maintenance hemodialysis (MHD). DESIGN: Observational study. SETTING: Outpatient dialysis units and a fall clinic. SUBJECTS: One hundred eight MHD and 122 elderly nonhemodialysis (non-HD) participants. EXPOSURE VARIABLE: Mid-thigh muscle area was measured by magnetic resonance imaging. MAIN OUTCOME MEASURE: Physical function was measured by distance walked in 6 minutes. RESULTS: Compared with non-HD elderly participants, MHD participants were younger (49.2 ± 15.8 vs. 75.3 ± 7.1 years; P < .001) and had higher mid-thigh muscle area (106.2 ± 26.8 vs. 96.1 ± 21.1 cm2; P = .002). However, the distance walked in 6 minutes was lower in MHD participants (322.9 ± 110.4 vs. 409.0 ± 128.3 m; P < .001). In multiple regression analysis adjusted for demographics, comorbid conditions, and mid-thigh muscle area, MHD patients walked significantly less distance (-117 m; 95% confidence interval: -177 to -56 m; P < .001) than the non-HD elderly. CONCLUSIONS: Even when compared with elderly non-HD participants, younger MHD participants have poorer physical function that was not explained by muscle mass or comorbid conditions. We speculate that the uremic milieu may impair muscle function independent of muscle mass. The mechanism of impaired muscle function in uremia needs to be established in future studies.

Effects of practice on variability of muscle force.

The motor skill required to decrease the variability in muscle force steadiness can be challenging. The purposes of this study were to determine whether muscle force steadiness improved following repeated trials and whether the number of trials varied for healthy younger adults, healthy older adults, and older adults who have fallen to obtain stable muscle force steadiness measures. Sixty participants performed 30 concentric and eccentric contractions of the knee extensors on an isokinetic dynamometer. Each group had significant improvements in muscle force steadiness and obtained stable measures within six to nine trials. Healthy younger and older adults, and older adults who have fallen, can improve muscle force steadiness. These findings provide a framework for methodological approaches when testing steadiness in varying populations.

Muscle force steadiness in older adults before and after total knee arthroplasty.

The ability to control submaximal muscle forces has been shown to be associated with age-related decreases in physical function, such as increased tendency to fall. This study compared quadriceps muscle force steadiness (MFS) in individuals with knee OA before and after total knee arthroplasty (TKA) to an age-matched group of controls. Lower extremity MFS was measured in 13 subjects with knee OA before and at six months after TKA (TKA-GROUP) and compared to an age-matched control group (CONTROL-GROUP). MFS was significantly more impaired in the TKA-GROUP at the pre-operative, but not post-operative visit, and significantly improved between the pre-operative and post-operative visits. Further research is warranted to evaluate the relation between this MFS measurement and physical functional performance in those at high risk for falling.

Eccentric arm cycling: physiological characteristics and potential applications with healthy populations.

INTRODUCTION: Eccentric leg cycling has served as an important research model for investigating multi-joint eccentric actions and as an effective rehabilitation and training modality for improving locomotor muscle function (e.g., quadriceps size, strength, mobility). While there are more than 30 reports documenting physiological responses to eccentric leg cycling, physiological responses to eccentric arm cycling (ECarm) have not been clearly established. PURPOSE: We tested the hypothesis that ECarm could be performed with lower levels of metabolic and cardiorespiratory demand and perceived exertion compared to traditional concentric arm cycling (CCarm). METHODS: Eight individuals performed ECarm and CCarm at 40, 80, and 120 W (~9 min, 60 rpm) while expired gases and muscle activation patterns were recorded. RESULTS: Oxygen consumption, cardiac output, heart rate, and ventilation were 25-50 % lower during ECarm compared to CCarm (all P < 0.05). Further, only low-to-moderate levels of whole-body and arm-specific perceived exertion were required to perform ECarm which was not the case for CCarm (8-12 vs. 9-16 Borg values, both P < 0.05). Differences in oxygen consumption and total upper body muscle activity between ECarm and CCarm were strongly related (r (2) = 0.75, P < 0.01). Coordination of ECarm involved triceps brachii, deltoideus anterior, and external oblique muscles, whereas CCarm involved all of these muscles along with contributions from biceps brachii, deltoideus posterior, and trapezius transversalis. CONCLUSIONS: These results highlight the high-force, low-cost nature of multi-joint eccentric actions and extend the application of eccentric cycling to the upper body. ECarm may be useful for exercising elbow, trunk, and shoulder musculature while minimizing metabolic and cardiorespiratory strain and perceived exertion.

Intramuscular adipose tissue and central activation in older adults.

INTRODUCTION: Intramuscular adipose tissue (IMAT) is a potential contributor to declining force production and may be related to impaired central activation; therefore, the purpose of this report is to describe IMAT composition and its association with central activation in older adults. The central activation ratio (CAR) of the knee extensors was assessed using a superimposition technique in 15 older adults (29 legs) along with the cross-sectional area of IMAT and lean tissue. RESULTS: IMAT and CAR are inversely related in older adults (r = -0.51, P = 0.005), and many subjects with high IMAT have deficits in central activation, whereas those with low IMAT have normal central activation. CONCLUSIONS: These novel findings may assist in unraveling why muscle force production and lean tissue cross-sectional area are not strongly linked, as the ability to centrally activate muscle appears to be unrelated to lean muscle area and may be dependent in part on IMAT levels.

Short-term exposure to a clinical dose of metformin increases skeletal muscle mitochondrial H2O2 emission and production in healthy, older adults: A randomized controlled trial.

BACKGROUND AND AIMS: Metformin is the most commonly prescribed medication to treat diabetes. Emerging evidence suggests that metformin could have off target effects that might help promote healthy muscle aging, but these effects have not been thoroughly studied in glucose tolerant older individuals. The purpose of this study was to investigate the short-term effects of metformin consumption on skeletal muscle mitochondrial bioenergetics in healthy older adults. METHODS: We obtained muscle biopsy samples from 16 healthy older adults previously naïve to metformin and treated with metformin (METF; 3F, 5M), or placebo (CON; 3F, 5M), for two weeks using a randomized and blinded study design. Samples were analyzed using high-resolution respirometry, immunofluorescence, and immunoblotting to assess muscle mitochondrial bioenergetics, satellite cell (SC) content, and associated protein markers. RESULTS: We found that metformin treatment did not alter maximal mitochondrial respiration rates in muscle compared to CON. In contrast, mitochondrial H2O2 emission and production were elevated in muscle samples from METF versus CON (METF emission: 2.59 ± 0.72 SE Fold, P = 0.04; METF production: 2.29 ± 0.53 SE Fold, P = 0.02). Furthermore, the change in H2O2 emission was positively correlated with the change in type 1 myofiber SC content and this was biased in METF participants (Pooled: R2 = 0.5816, P = 0.0006; METF: R2 = 0.674, P = 0.0125). CONCLUSIONS: These findings suggest that acute exposure to metformin does not impact mitochondrial respiration in aged, glucose-tolerant muscle, but rather, influences mitochondrial-free radical and SC dynamics. CLINICAL TRIAL REGISTRATION: NCT03107884, clinicaltrials.gov.

Muscle damage and muscle remodeling: no pain, no gain?

Skeletal muscle is a dynamic tissue that responds adaptively to both the nature and intensity of muscle use. This phenotypic plasticity ensures that muscle structure is linked to patterns of muscle use throughout the lifetime of an animal. The cascade of events that result in muscle restructuring - for example, in response to resistance exercise training - is often thought to be initiated by muscle damage. We designed this study to test the hypothesis that symptomatic (i.e. detectable) damage is a necessary precursor for muscle remodeling. Subjects were divided into two experimental populations: pre-trained (PT) and naive (NA). Demonstrable muscle damage was avoided in the PT group by a three-week gradual 'ramp-up' protocol. By contrast, the NA group was subjected to an initial damaging bout of exercise. Both groups participated in an eight-week high-force eccentric-cycle ergometry program (20 min, three times per week) designed to equate the total work done during training between the groups. The NA group experienced signs of damage, absent in the PT group, as indicated by greater than five times higher levels of plasma creatine kinase (CK) and self-reporting of initial perceived soreness and exertion, yet muscle size and strength gains were not different for the two groups. RT-PCR analysis revealed similar increases in levels of the growth factor IGF-1Ea mRNA in both groups. Likewise, the significant (P<0.01) increases in mean cross-sectional area (and total muscle volume) were equal in both groups. Finally, strength increases were identical for both groups (PT=25% and NA=26% improvement). The results of this study suggest that muscle rebuilding - for example, hypertrophy - can be initiated independent of any discernible damage to the muscle.

Effects of high-intensity resistance training on strength, mobility, balance, and fatigue in individuals with multiple sclerosis: a randomized controlled trial.

BACKGROUND AND PURPOSE: Resistance exercise via negative, eccentrically induced work (RENEW) has been shown to be associated with improvements in strength, mobility, and balance in multiple clinical populations. However, RENEW has not been reported for individuals with multiple sclerosis (MS). METHODS: Nineteen individuals with MS (8 men, 11 women; age mean = 49 ± 11 years; Expanded Disability Status Scale [EDSS] mean = 5.2 ± 0.9) were randomized into either standard exercise (STAND) or standard exercise and RENEW training (RENEW) for 3×/week for 12 weeks. Outcome measures were lower extremity strength (hip/knee flexion and extension, ankle plantar and dorsiflexion, and the sum of these individual values [sum strength]); Timed Up and Go (TUG), 10-m walk, self-selected pace (TMWSS) and maximal-pace (TMWMP), stair ascent (S-A) and descent (S-D) and 6-Minute Walk Test (6MWT), Berg Balance Scale (BBS), Fatigue Severity Scale (FSS). RESULTS: No significant time effects or interactions were observed for strength, TUG, TMWSS, TMWMP, or 6MWT. However, the mean difference in sum strength in the RENEW group was 38.60 (representing a 15% increase) compared to the sum strength observed in the STAND group with a mean difference of 5.58 (a 2% increase). A significant interaction was observed for S-A, S-D, and BBS as the STAND group improved whereas the RENEW group did not improve in these measures. DISCUSSION AND CONCLUSIONS: Contrary to results in other populations, the addition of eccentric training to standard exercises did not result in significantly greater lower extremity strength gains in this group of individuals with MS. Further this training was not as effective as standard exercise alone in improving balance or the ability to ascend and descend stairs. Following data collection, reassessment of required sample size indicates we were likely underpowered to detect strength differences between groups.

Eccentric exercise versus usual-care with older cancer survivors: the impact on muscle and mobility--an exploratory pilot study.

BACKGROUND: Resistance exercise programs with high compliance are needed to counter impaired muscle and mobility in older cancer survivors. To date outcomes have focused on older prostate cancer survivors, though more heterogeneous groups of older survivors are in-need. The purpose of this exploratory pilot study is to examine whether resistance exercise via negative eccentrically-induced work (RENEW) improves muscle and mobility in a diverse sample of older cancer survivors. METHODS: A total of 40 individuals (25 female, 15 male) with a mean age of 74 (± 6) years who have survived (8.4 ± 8 years) since their cancer diagnosis (breast, prostate, colorectal and lymphoma) were assigned to a RENEW group or a non-exercise Usual-care group. RENEW was performed for 12 weeks and measures of muscle size, strength, power and mobility were made pre and post training. RESULTS: RENEW induced increases in quadriceps lean tissue average cross sectional area (Pre: 43.2 ± 10.8 cm2; Post: 44.9 ± 10.9 cm2), knee extension peak strength (Pre: 248.3 ± 10.8 N; Post: 275.4 ± 10.9 N), leg extension muscle power (Pre: 198.2 ± 74.7 W; Post 255.5 ± 87.3 W), six minute walk distance (Pre: 417.2 ± 127.1 m; Post 466.9 ± 125.1 m) and a decrease on the time to safely descend stairs (Pre: 6.8 ± 4.5 s; Post 5.4 ± 2.5 s). A significant (P < 0.05) group x time interaction was noted for the muscle size and mobility improvements. CONCLUSIONS: This exploration of RENEW in a heterogeneous cohort of older cancer survivors demonstrates increases in muscle size, strength and power along with improved mobility. The efficacy of a high-force, low perceived exertion exercise suggests RENEW may be suited to older individuals who are survivors of cancer.

Longitudinal study of knee load avoidant movement behavior after total knee arthroplasty with recommendations for future retraining interventions.

BACKGROUND: This study aimed to evaluate clinical and biomechanical changes in self-report survey, quadriceps strength and gait analysis over 3- and 6-months post-total knee arthroplasty (TKA) and confirm the immediate effects of two forms of kinetic biofeedback on improving inter-limb biomechanics during a physically demanding decline walking task. METHODS: Thirty patients with unilateral TKA underwent testing at 3- and 6-months following surgery. All underwent self-report survey, quadriceps strength and gait analysis testing. Patients were assigned to one of two types of biofeedback [vertical ground reaction force (vGRF), knee extensor moment (KEM)]. RESULTS: No decrease in gait asymmetry was observed in non-biofeedback trials over time (p > 0.05), despite significant improvements in self-report physical function (p < 0.01, Cohen d = 0.44), pain interference (p = 0.01, Cohen d = 0.68), numeric knee pain (p = 0.01, Cohen d = 0.74) and quadriceps strength (p = 0.01, Cohen d = 0.49) outcomes. KEM biofeedback induced significant decrease in total support moment (p = 0.05, Cohen f2 = 0.14) and knee extensor moment (p = 0.05, Cohen f2 = 0.21) asymmetry compared to using vGRF biofeedback at 6-months. vGRF biofeedback demonstrated significant decrease in hip flexion kinematic asymmetry compared to KEM biofeedback (p = 0.05, Cohen f2 = 0.18) at 6-months. CONCLUSION: Gait compensation remained similar from 3- to 6-months during a task requiring greater knee demand compared to overground walking post-TKA, despite improvements in self-report survey and quadriceps strength. Single session gait symmetry training at 6-month supports findings at 3-month testing that motor learning is possible. KEM biofeedback is more effective at immediately improving joint kinetic loading compared to vGRF biofeedback post-TKA.

The feasibility and efficacy of eccentric exercise with older cancer survivors: a preliminary study.

INTRODUCTION: Older individuals who have survived cancer and the commensurate treatment often experience a reduced quality of life in part due to their impaired muscular abilities and deficits in mobility. The purpose of this preliminary study was to determine the feasibility and preliminary efficacy of resistance exercise via negative, eccentrically induced work (RENEW) with older cancer survivors. METHODS: Older cancer survivors with a perception of moderate muscle weakness and fatigue participated in 12 weeks of RENEW. Measures of feasibility included (1) the participant's ability to progress the total amount of work of RENEW; (2) whether peak knee extension torque production became impaired; and (3) whether RENEW induced leg muscle pain as measured on a visual analog scale. The preliminary measure of efficacy included the performance of a timed up-and-go mobility test. RESULTS: The participants significantly increased the total average work per week over the 12 weeks of RENEW. Participants increased (P < .001) their work approximately 3-fold from week 3 (7.6 [5.11 kJ) to week 12 (22.1 [14.8] kJ) without muscle pain over the 12-week RENEW training period. Knee extension peak torque production improved (11%) significantly (P = .02) (pretest: 248 [92] N; posttest: 275 [99] N) after 12 weeks of RENEW. The time to perform the up-and-go test improved (14%) significantly (P < .001) (pretest: 8.4 [2.7]; posttest: 7.2 [2.3] s) after 12 weeks of RENEW, suggesting preliminary efficacy. CONCLUSION: Collectively, RENEW appears feasible and potentially efficacious for older, weak, and fatigued cancer survivors. IMPLICATIONS FOR CANCER SURVIVORS: The use of eccentric muscle exercise may be ideally suited for older cancer survivors due to its high force and low energetic-cost capabilities.

Exercise and lung cancer surgery: A systematic review of randomized-controlled trials.

Lung cancer patients undergoing surgery are often left physically deconditioned and/or with functional deficits. Exercise interventions may improve pulmonary and physical function before and after lung resection. We conducted a systematic review of randomized-controlled trials (RCTs) testing the impact of pre-, post-, and combined pre-and-post surgery exercise interventions on physical and pulmonary function in lung cancer patients. Exercise pre-surgery seems to substantially improve physical and pulmonary function, which are factors associated with improved ability to undergo surgery while reducing post-surgery complications. Evidence is inconsistent for post-surgery interventions, reporting no or moderate effects. Results from pre-and-post surgery interventions are limited to one study. In conclusion, pre- and post-surgery exercise interventions, individually, have shown beneficial effects for lung cancer patients undergoing surgery. The impact of interventions combining both pre- and post-surgery exercise programs remains unknown. More evidence is needed on the ideal exercise setting, and timing across the lung cancer care continuum.

Physical Function in the Hospital Is Associated With Patient-Centered Outcomes in an Inpatient Rehabilitation Facility.

OBJECTIVE: Poor knowledge of the relationships between physical function (PF) in the hospital and patient outcomes in an inpatient rehabilitation facility (IRF) limits the identification of patients most appropriate for discharge to an IRF. This study aimed to test for independent associations between PF measured via the AM-PAC "6-clicks" basic mobility short form in the hospital and outcomes in an IRF. METHODS: This was a retrospective cohort study. Primary data were collected from an acute hospital and IRF at 1 academic medical center. Associations were tested between PF at hospital admission or discharge and PF improvement in the IRF, discharge from the IRF to the community, and 30-day hospital events by estimating adjusted relative risk (aRR) using modified Poisson regression and the relative difference in IRF length of stay (LOS) using Gamma regression. RESULTS: A total of 1323 patients were included. Patients with moderately low, (aRR = 1.50; 95% CI = 1.15-1.93), moderately high (aRR = 1.52; 95% CI = 1.16-2.01), or high (aRR = 1.37; 95% CI = 1.02-1.85) PF at hospital discharge were more likely than those with very low PF to improve their PF while in the IRF. These same patients were more likely to discharge from IRF to the community and had significantly shorter IRF LOS. Hospital-measured PF did not differentiate risk for 30-day hospital events. CONCLUSION: Patients with moderate-but not very low or very high-PF measured near the time of acute hospital discharge were likely to achieve meaningful PF improvement in an IRF. They also had a shorter IRF LOS so may be ideal candidates for discharge to IRF. Prospective studies with larger samples are necessary to test this assertion. IMPACT: Providers in the hospital should identify patients with moderate PF near the time of hospital discharge as those who may benefit most from post-acute rehabilitation in an IRF.

Clinically Integrated Physical Therapist Practice in Cancer Care: A New Comprehensive Approach.

Best practice recommendations in cancer care increasingly call for integrated rehabilitation services to address physical impairments and disability. These recommendations have languished primarily due to a lack of pragmatic, generalizable intervention models. This perspective paper proposes a clinically integrated physical therapist (CI-PT) model that enables flexible and scalable services for screening, triage, and intervention addressing functional mobility. The model is based on (1) a CI-PT embedded in cancer care provider clinics, and (2) rehabilitation across the care continuum determined by the patient's level of functional mobility. The CI-PT model includes regular screening of functional mobility in provider clinics via a patient-reported mobility measure-the Activity Measure for Post-Acute Care, a brief physical therapy evaluation tailored to the specific functional needs of the individual-and a tailored, skilled physical therapist intervention based on functional level. The CI-PT model provides a pragmatic, barrier-free, patient-centric, data-driven approach to integrating rehabilitation as part of standard care for survivors of cancer. The model standardizes CI-PT practice and may be sufficiently agile to provide targeted interventions in widely varying cancer settings and populations. Therefore, it may be ideal for wide implementation among outpatient oncological settings. Implementation of this model requires a shared approach to care that includes physical therapists, rehabilitation administrators, cancer care providers, and cancer center administrators.

Reversing muscle and mobility deficits 1 to 4 years after TKA: a pilot study.

UNLABELLED: Muscle and mobility deficits can persist for years after a total knee arthroplasty (TKA). The purposes of this study were (1) to determine if 12 weeks of rehabilitation with resistance exercise induces increases in muscle size, strength, and mobility in individuals 1 to 4 years after a TKA; and (2) to compare the muscle and mobility outcomes of a traditional resistance exercise rehabilitation program with a rehabilitation program focused on eccentric resistance exercise. Seventeen individuals (13 women, four men; mean age, 68 years; age range, 55-80 years) with either a unilateral or bilateral TKA (total of 24 knees) were included in this matched and randomized repeated-measures rehabilitation pilot trial. Increases in quadriceps muscle volume and knee extension strength followed 12 weeks of eccentric exercise. Improvements were also noted in four mobility tests. Similar improvements were noted in the traditional group in two mobility tests. An increase in muscle size and strength and an improvement in levels of mobility can occur after 12 weeks of resistance exercise in older individuals 1 to 4 years after TKA. When the exercise mode focuses on eccentric resistance, the muscle growth response is greater as is the improvement in important mobility tasks. LEVEL OF EVIDENCE: Level II, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

The long-term contribution of muscle activation and muscle size to quadriceps weakness following total knee arthroplasty.

PURPOSE: Many older individuals have persistent quadriceps strength impairments after a total knee arthroplasty (TKA). A combination of muscle atrophy and neuromuscular activation deficits apparently contributes to residual strength impairments. The purpose of this short report is to describe the contribution of quadriceps muscle activation and muscle volume to impaired muscle strength in older individuals an average of 21 months following a TKA. METHODS: Seventeen individuals (males: 3, females: 14; mean age: 68 yrs +/- 8.7; BMI: 33 +/- 4.8 kg/m2; number of TKA: 24; average postoperative months: 21 +/- 11.3) recruited from an orthopaedic surgeon's practice provided their written consent and participated in this study. Quadriceps strength (MVIC) and voluntary quadriceps muscle activation (QA) were measured with use of a burst-superimposition technique in which a supramaximal burst of electrical stimulation is superimposed on an MVIC. Quadriceps volume (QV) was assessed from magnetic resonance images of the quadriceps. RESULTS: The mean quadriceps strength was 107.3 Nm +/- 36.4 (range: 43.22 - 205.2). The mean QA (as described with a central activation ratio) was 0.97 +/- 0.04 (range: 0.83 - 1.00). The mean QV was 1093 cm3 +/- 311.80 (range: 653.66 - 1706.56). QA and QV explain 85% of the variance in quadriceps strength (R2 = .85, p < 0.001), with QV having the greatest contribution to strength (R2 = .77, p < 0.001). CONCLUSIONS: QV is a much stronger predictor of quadriceps strength than QA in individuals more than 1 year following TKA. Activation levels contributed little to strength one year following TKA, compared to its profound contribution in the first few postoperative months. Physical therapy interventions focused on improving muscle size in this population should be considered more relevant than countermeasures addressing neuromuscular activation.