Muscle adaptation and disability in late poliomyelitis

Abstract

Persons who suffered poliomyelitis 3 or more decades ago now report functional decline and symptoms designated as "post-polio syndrome". The objects of this investigation were to identify subjects fulfilling the criteria of this syndrome, to describe their motor impairment and resulting disabilities/handicaps, to study the adaptive changes in the muscle structure and effects of a resistance exercise program. Forty-one late-polio subjects, 40-65 years old, volunteered for the studies of motor impairment, subgroups of those volunteered to further studies of long-term and short-term adaptations. Seventy-five per cent of the subjects met the criteria for the post-polio syndrome. Complete manual muscle tests and dynamometer measurements of knee muscle strength revealed severe motor impairment predominantly in the lower extremities, the strength of the latter correlating to the degree of mobility handicap. In biopsies from the vastus lateralis muscle, type grouping was frequent. Half of the subjects demonstrated over 70% occurrence of type I fibers with negative significant correlation to strength in the female subjects. Cross-section areas of muscle fibers were on average twice the normal, with negative significant correlation to strength values in male subjects. Muscle enzymatic activity values showed large individual variations; oxidative activities (citrate synthase) were low or very low, while average glycolytic activities were nearly normal. Macro EMG and single-fiber EMG measurements in the vastus lateralis muscle demonstrated large macro motor unit potentials and increased fiber density. Neuromuscular transmission was disturbed as identified by jitter and blockings in most subjects regardless of the occurrence of new muscular symptoms. A statistically significant increase in strength (25-30%) resulted from a 6 weeks' heavy resistance exercise program, utilizing a dynamometer, without any obvious side-effects. Strength improvement was maintained for 6-12 months after training while fatigue index increased. A substantial impact on intermediate (secondary or instrumental) ADL, most severely affecting the quality of mobility, was generally found, while little effect was found on primary ADL as revealed by the Katz' ADL index, the Functional Status Questionnaire and the WHO ICIDH Classification of Handicap. The impaired motor function confirms findings in earlier studies. It also corresponds with the locomotor disabilities and handicaps. The negative correlation of strength to cross-section fiber area might result from excessive use of remaining fibers leading to a prominent hypertrophy in the weakest subjects. Enzyme activities probably reflect the pattern of everyday activities with little demands on endurance.(ABSTRACT TRUNCATED AT 400 WORDS)