Muscle force and movement variability before and after total knee arthroplasty: A review

Table 1 Summary of the literature addressing muscle force output variability in older adults and those with osteoarthritis before and after total knee arthroplasty

Study	Population	Purpose/hypothesis	Variables assessed	Significant findings
Older adults with native, non-arthritic knees
Carville et al[50], 2007	n = 44 (Young adults; Age range = 18-4 yr) n = 78 (Older adults; Age range > 70 yr)	To investigate isometric and anisometric quadriceps contractions in healthy you and older adults	Muscle strength; CV of isometric force steadiness at 10%, 25%, and 50% of MVC; and SD of acceleration of anisometric steadiness during concentric and eccentric contractions against two external loads of 1 and 5 kg	1. Non-significant trend for younger subjects to be most steady and fallers least study 2. Isometric force steadiness was unaffected by the level of force output. 3. Fallers were less steady than both young and non-fallers 4. Older adults were less steady during eccentric contractions than the younger adults and fallers were the least steady
Christou et al[51], 2002	n = 24 (Young, active adults; Mean age = 25.3 yr) n = 24 (Older active adults; Mean age = 73.3 yr)	To examine the ability to control knee-extension force during discrete isometric, concentric, and eccentric contractions	Muscle strength; Isometric force steadiness at 90 degrees of knee flexion; and Concentric and eccentric force steadiness at 25 deg/s	1. CV of force steadiness for all contractions was greater in older subjects than younger subjects 2. Muscle strength was similar for all three types of contractions Young subjects were stronger than older subjects
Hortobágyi et al[52], 2001	n = 27 (Older adults; Mean age = 72 yr) n = 10 (Young adults; Mean age = 21 yr)	To compare the effects of low- and high-intensity strength training o maximal and explosive strength and on the accuracy and steadiness of submaximal quadriceps force in elderly humans	Muscle strength Quadriceps force accuracy and steadiness during isometric, concentric and eccentric contractions performed at 25 N target force	1. Older subjects had significantly more force variability (i.e., were less steady) during eccentric and concentric, but not isometric contractions 2. Force variability and accuracy were correlated with each other, but not with maximal strength 3. Training significantly improved force accuracy and variability during eccentric and concentric contractions
Manini et al[53], 2005	n = 50 (Healthy, older adults; Mean age = 76.2 yr)	To determine how knee extensor steadiness during an isometric task is related to performing four everyday tasks that included chair rising, walking at a fast pace, and stair ascending and descending	Isometric knee extensor steadiness at 50%MVC; Chair rise time Time to ascend and descend stairs; and Walking velocity	Isometric quadriceps force steadiness was not a predictor of functional performance in older subjects
Schiffman et al[54], 2001	n = 19 (Healthy older adults; Mean age = 71.8 yr) n = 20(Healthy young adults; Mean age = 25.8 yr)	To investigate the effects of motion on submaximal force control abilities in the knee extensors	Isokinetic force variability at two different force levels; 20% of MVC and 60% of MVC	1. Isokinetic submaximal force control was equally diminished in both young and older adults compared to isometric force control 2. As the force level increased, force variability decreased for both young and older adults
Tracy et al[22], 2002	n = 10 (Healthy young adults; Mean age = 22 yr) n = 10 (Healthy older adults; Mean age = 72 yr)	To compare the steadiness and EMG activity of young and old adults while they were performing submaximal isometric and anisometric contractions with the knee extensor muscles	Muscle strength; EMG of quadriceps muscles during experimental tasks; and Isometric, concentric, and eccentric force steadiness for 10-12 s at 2%, 5%, 10%, and 50% of MVC	1. Steadiness of old adults was reduced compared with young adults during isometric, but not during concentric and eccentric contractions 2. Decline in steadiness was not associated with differences in EMG magnitude
Tracy et al[55], 2004	n = 26 (Healthy, older adults; Mean age = 77.7 yr)	To determine the effect of strength and steadiness training with heavy loads by old adults on the fluctuations in force and position during voluntary contractions with the quadriceps femoris muscles	Muscle strength (MVC); Force fluctuations during isometric contractions at 2%, 5%, 10%, and 50% of MVC; Force fluctuations during concentric and eccentric contractions at 5%, 10%, and 50% of MVC; EMG activity of the quadriceps muscles during experimental tasks; and Physical function tasks including gait speed, chair rise, and stair ascent and descent	1. Force fluctuations during submaximal isometric contractions did not change with training 2. Force fluctuations during submaximal anisometric contractions with a 50% load declined for both heavy and light training groups
Seynnes et al[13], 2005	n = 19 (Healthy older women; Mean age = 77.9 yr)	To assess the relationship between knee-extensor force-control capacity, as measured by isometric force steadiness and accuracy, and functional limitations in healthy older adults	Isometric quadriceps force steadiness at 50% of MVC; MVC Rate of torque development; EMG activity; and Functional performance measures including walking endurance, chair rising, and stair climbing	1. Isometric steadiness independently predicts chair-rise time and stair-climbing power 2. None of the accuracy measures were significantly associated with any of the functional performance tests Walking endurance was related to muscle strength, but not steadiness
Older adults with osteoarthritic knees
Hortobágyi et al[56], 2004	n = 20 (Older adults with OA; Mean age = 57.5 yr) n = 20 (Controls; Mean age = 56.8 yr)	To characterize the distribution of error in knee joint proprioception, quadriceps force accuracy and steadiness and muscle strength in patients with knee OA	Quadriceps force accuracy and steadiness during a force target-tracking task during anisometric contractions. Muscle strength was measured during eccentric, isometric, and concentric contractions	1. Knee OA subjects needed 67% more time to complete functional tasks, produced 82% more proprioception errors, and 89% more errors in accurately matching target forces 2. Knee OA subjects had 155% more force variability, with eccentric contractions being particularly unsteady
Sørensen et al[57], 2011	n = 41 (Older adults with OA; Mean age = 62 yr)	To investigate the relationship between quadriceps force steadiness and knee adduction moment during walking in patients with knee OA	Submaximal isometric quadriceps force steadiness during a force target-tracking task. Peak knee adduction moment during ambulation	Quadriceps force steadiness does not predict peak knee adduction moment
Older adults following total knee arthroplasty
Smith et al[14] ,2013	n = 13 (Older adults with TKA; Mean age = 62.7 yr) n = 11 (Controls; Mean age = 62.2 yr)	To compare muscle force steadiness of submaximal quadriceps force output in individuals with knee OA before and after TKA, and to a group of age-matched controls with native knees	Muscle strength; Quadriceps muscle force steadiness (MFS) during anisometric eccentric and concentric contractions at 50% MVIC	1. Pre-operatively, quadriceps force steadiness for both concentric and eccentric contractions was significantly higher in the OA group relative to controls; and 2. Post-operatively quadriceps force steadiness for both concentric and eccentric contractions was significantly lower in the OA group relative to controls Muscle strength was significantly lower in the TKA group both pre- and post-operatively compared to controls

CV: Coefficient of variation; MVC: Maximal voluntary contraction; OA: Osteoarthritis; TKA: Total knee arthroplasty; EMG: Electromyographic signal.