Alterations in human muscle and central control mechanisms

Research has shown that skeletal muscle, despite showing a high degree of
specialisation, has a remarkable ability to modify its properties. Understanding these
changes is important for optimal response to therapeutic intervention. These studies
investigated alterations in neuromuscular performance of quadriceps femoris muscle in
normal subjects, before investigating changes in muscle and neural mechanisms in the
first six months following stroke.
Muscle function studies were conducted to monitor the effects of selected patterns of
long term electrical stimulation (PI - uniform 8 Hz, P2 - mixed frequency, and P3
random high and low frequency) on quadriceps femoris of 21 healthy subjects.
Stimulated muscles showed significant increases in strength, fatigue resistance and
relaxation times after 3 weeks and in force-frequency output after 6 weeks. Significant
changes were observed in the stimulated muscles in Groups P2 and P3 indicating that a
mixed or random pattern of activation induced greater changes than a uniform 8 Hz
pattern.
These studies together with soleus H reflexes were used to study concurrent changes
in quadriceps femoris and la spinal reflex pathways of stroke patients and age-matched
controls (n=10). One month following stroke, both paretic and non-paretic muscles
were more fatiguable and weaker than the muscles of controls and disynaptic and
presynaptic inhibition were reduced in the paretic limbs. In subsequent months, the
paretic muscles regained strength and inhibitory effects were restored.
Subjective analysis suggested that different patterns of recovery related to walking
ability at six months. In patients taking less than 15s to walk 10m (Group 1 n=5), the
paretic muscles became significantly stronger and less fatiguable over time whereas the
muscles of patients who took longer to walk 10m (Group 2 n=5) remained weaker and
more fatiguable. Reciprocal inhibition was regained by 1 month in Group 1 and by 6
months in Group 2. These findings provide insight into long-term recovery and
rationale for therapeutic intervention following stroke.

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