Intrinsic muscle strength and voluntary activation of both lower limbs and functional performance after stroke

Abstract

SummaryThe objective of this study was to assess the nature of muscle weakness in both legs after stroke compared with able-bodied control individuals and to examine whether there is a relationship between the degree of muscle weakness and coactivation of knee extensors and flexors as well as voluntary activation capacity of knee extensors of both paretic and non-paretic legs and indices of functional performance. Maximal voluntary isometric torques of knee extensors (MVCe) and flexors (MVCf) were determined in 14 patients (bilaterally) and 12 able-bodied controls. Simultaneous measurements were made of torque and surface EMG from agonist and antagonist muscles. Coactivation was calculated. Supramaximal triplets were evoked with electrical stimulation to estimate maximal torque capacity and degree of voluntary activation of knee extensors. MVCs, activation and coactivation parameters were correlated to scores of seven functional performance tests. MVCe, MVCf and voluntary activation were lower in paretic lower limb (PL) compared with both non-paretic lower limb (NL) and control. Besides, all these parameters of NL were also lower than control. Electrically evoked torque capacity of knee extensors of PL was about 60% of both NL and control, which were not significantly different from each other. Strong significant correlations between strength, as well as voluntary activation, and functional performance were found. Coactivation did not correlate well with functional performance. Thus, whereas for NL activation failure can explain weakness, for PL both activation failure and reduced intrinsic torque capacity are responsible for the severe weakness. Activation capacity and muscle strength correlated strongly to functional performance, while coactivation did not.

Functional recovery and muscle properties after stroke: a preleminary longitudinal study

“…Patients (characteristics: see Table 1), all with first-ever stroke and a hemiparesis of the lower extremity, entered the study on average 3.5 months after stroke and 2 months after admission in the rehabilitation centre (t=0). Data on muscle function in relation to functional performance of these patients at t=0 are reported elsewhere (Horstman et al, 2008). They were invited for measurements again 3 (n=8), 6 (n=5) and 12 (n=3) months after the first measurement (follow-up (F)1, F2 and F3 respectively).…”

“…Briefly, maximal voluntary and electrically evoked isometric torques of the knee extensors and maximal voluntary isometric torques of the knee flexors were measured while subjects were seated on a custom built Lower EXtremity System (LEXS) (Horstman et al, 2008). The lower leg was strapped tightly to a force transducer just above the ankle by means of a cuff at a knee flexion angle of 60 (0 = full extension).…”

“…The procedures for the measurements as well as the calculation of variables are described in detail elsewhere (Horstman et al, 2008). Briefly, maximal voluntary and electrically evoked isometric torques of the knee extensors and maximal voluntary isometric torques of the knee flexors were measured while subjects were seated on a custom built Lower EXtremity System (LEXS) (Horstman et al, 2008).…”

“…Nevertheless, most studies are performed at one point in time (Kim & Eng, 2003;Mercier & Bourbonnais, 2004;Ada et al, 2006;Bohannon, 2007b;Patterson et al, 2007;Horstman et al, 2008). It is not fully elucidated whether the improvements in functional performance at the activity level of patients with stroke during rehabilitation relate to changes in specific contractile function of the thigh muscles.…”

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

“…This method can be used not only in fundamental research but also in the clinical domain 76 . Indeed, electrical nerve stimulation has been used to investigate central drive in the elderly 77 and different diseases such as stroke 78 or Parkinson's disease 79 . Neuromuscular plasticity can also be assessed in pathological populations during therapy/retraining program 80 .…”