Muscle strength in postpolio patients: A prospective follow-up study

Forty-three former polio patients now complaining of new progressive muscle weakness (symptomatic patients) plus 13 former polio patients without new neuromuscular complaints were included in the study. The symptomatic patients reported high frequencies of other neuromuscular complaints and a decline in their functional level. Most frequent complaints were general fatigue, low backache, and muscle pain (97.7%, 86%, and 79.1%, respectively) and a decline in the ability to walk (80%). In a prospective follow-up averaging 2.1 years, the muscle strength of 26 muscles in all four limbs of each patient was assessed by manual muscle testing and was also measured isometrically using a handheld dynamometer. During the follow-up period, we did not find a significant decrease in muscle strength in the symptomatic patients as compared to patients without new neuromuscular complaints. © 1996 John Wiley & Sons, Inc.     

Postpolio muscular dysfunction: Relationships between muscle energy metabolism,subjective symptoms,magnetic resonance imaging,electromyography, and muscle strength

Eleven patients with previous polio were studied. The concentration of energy-related metabolites and energy charge was measured from the vastus lateralis muscle, as was isometric muscle strength of knee extension. Cross-sectional area of the quadriceps femoris muscle was calculated from magnetic resonance imaging. Reinnervation was studied using macroelectromyography. Muscle weakness, pain, and newly acquired muscle weakness in the legs was estimated by the patients. The findings in the legs in which the patients experienced new loss of muscle function were compared with the stable legs. There were no significant differences between these groups in any of the objectively measured variables. Only hip pain correlated with new loss of muscle function. Creatine phosphate was decreased in 5 patients. The symptoms and subjective muscle strength did not correlate with any of the objective measurements. There were no significant relationships between energy-related metabolites and postpolio symptoms. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 1341–1351, 1997     

Resistance strength training exercise in children with spinal muscular atrophy

Introduction: Preliminary evidence in adults with spinal muscular atrophy (SMA) and in SMA animal models suggests exercise has potential benefits in improving or stabilizing muscle strength and motor function. Methods: We evaluated feasibility, safety, and effects on strength and motor function of a home‐based, supervised progressive resistance strength training exercise program in children with SMA types II and III. Up to 14 bilateral proximal muscles were exercised 3 times weekly for 12 weeks. Results: Nine children with SMA, aged 10.4 ± 3.8 years, completed the resistance training exercise program. Ninety percent of visits occurred per protocol. Training sessions were pain‐free (99.8%), and no study‐related adverse events occurred. Trends in improved strength and motor function were observed. Conclusions: A 12‐week supervised, home‐based, 3‐day/week progressive resistance training exercise program is feasible, safe, and well tolerated in children with SMA. These findings can inform future studies of exercise in SMA. Muscle Nerve 52 : 559–567, 2015     

Computed tomographic study of the skeletal musculature of the lower body in 45 postpolio patients

Muscle computed tomography (CT) and muscle strength assessment of the pelvic girdle and leg muscles were performed in 32 postpolio patients experiencing new muscle weakness, and in 13 postpolio patients with stable neuromuscular condition. Muscles of the postpolio patients experiencing new muscle weakness showed significantly more CT scan abnormalities as compared with the stable postpolio patients. No other features discriminative of symptomatic postpolio patients were found. In individual patients, muscle CT scan evaluation is a useful adjunct to muscle strength assessment. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:540–542, 1998.     

Safety and efficacy of strength training in patients with sporadic inclusion body myositis

We studied the effects of a 12-week progressive resistance strength training program in weakened muscles of 5 patients with sporadic inclusion body myositis (IBM). Strength was evaluated with Medical Research Council (MRC) scale ratings and quantitative isometric and dynamic tests. Changes in serum creatine kinase (CK), lymphocyte subpopulations, muscle size (determined by magnetic resonance imaging), and histology in repeated muscle biopsies were examined before and after training. After 12 weeks, the values of repetition maximum improved in the least weakened muscles, 25–120% from baseline. This dynamic effect was not captured by MRC or isometric muscle strength measurements. Serum CK, B cells, T-cell subsets, and NK cells remained unchanged. Repeat muscle biopsies did not reveal changes in the number and degree of degenerating fibers or inflammation. The size of the trained muscles did not change. We conclude that a supervised progressive resistance training program in IBM patients can lead to gains in dynamic strength of the least weak muscles without causing muscle fatigue and muscle injury or serological, histological, and immunological abnormalities. Even though the functional significance of these gains is unclear, this treatment modality is a safe and perhaps overlooked means of rehabilitation of IBM patients. © 1997 John Wiley & Sons, Inc. Muscle Nerve 20: 1242–1248, 1997     

An 8-year longitudinal study of muscle strength,muscle fiber size,and dynamic electromyogram in individuals with late polio

Twenty-one subjects with polio 24 to 51 years prior to the first examination were studied on three occasions, each 4 years apart with measurements of muscle strength and endurance for knee extension, macro EMG, and muscle biopsy from vastus lateralis. On average the muscle strength decreased during the 8-year follow-up by 9–15%. Endurance decreased during the observation period. The muscle fiber area was markedly increased in most subjects. There was a decrease in the capillarization during the follow-up. Macro EMG was increased in all subjects (range 3–42 times control) and increased in 20 legs during the 8-year follow-up, but showed a decrease in 8 of 9 legs with an approximative breakpoint when macro MUPs were around 20 times the normal size. Thus, evidence of on-going denervation/reinnervation as well as of failing capacity to maintain large motor units was demonstrated. SFEMG showed a moderate degree of disturbed neuromuscular transmission. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1428–1437, 1998     

Lack of human muscle architectural adaptation after short-term strength training

The mechanisms governing the increases in force production in response to short periods of strength training have yet to be fully elucidated. We examined whether muscle architectural adaptation was a contributing factor. Ultrasound imaging techniques were used to measure quadriceps muscle architecture at 17 sites in vivo in trained and untrained legs of men and women after 2.5 and 5 weeks of unilateral knee extension training, as well as in a nontraining control group. Despite increases in knee extensor strength of the trained and untrained (women only) legs, there were no changes in muscle thickness, fascicle angle, or fascicle length in any of the muscles tested. The moderate correlation between vastus lateralis thickness (middle site) and eccentric (r = 0.55; P < 0.05) and concentric (r = 0.46; P < 0.1) torque after, but not before, training is suggestive of neural rather than architectural adaptations predominating in the early phase of training.     

Dynamic electromyography and muscle biopsy changes in a 4-year follow-up: Study of patients with a history of polio

Eighteen patients who had had polio 29–56 years prior to the first investigation were studied on two occasions, 4 years apart. Isokinetic and isometric strength measurements and Macro EMG were performed in 28 legs. Muscle biopsy specimens were obtained on both occasions from 11 legs. On average the muscle strength was 56% of control values at the first examination, and decreased by another 8% during the observation period. The muscle fiber area was increased compared to that of controls and did not change significantly. Macro EMG, comprising muscle fiber area and number of muscle fibers, and/or single fiber EMG showed clear signs of reinnervation in all legs. The motor units at the first examination were increased 11-fold, on average, compared with age-matched control values. During the observation period, reinnervation continued and the size of motor units increased by another 56% as a result of ongoing denervation, that is, loss of neurons. This compensation was particularly pronounced in patients with stable conditions. The parameters studied did not reveal any definite pattern predicting future development of new muscle weakness in individual subjects. © 1995 John Wiley & Sons, Inc.     

Fibrillation potential amplitude and muscle atrophy following peripheral nerve injury

Maximum peak-to-peak fibrillation potential amplitude was measured in 69 subjects between 7 days and 10 1/2 years post complete or partial peripheral nerve injury. Mean amplitude during the first 2 months was 612 muV; third and fourth months 512 muV, fifth and sixth months 320 muV. After the first year, no population of fibrillation potentials greater than 100 muV was recorded. The sciatic nerve was sectioned in 13 guinea pigs and animals studied up to 17 weeks. Fibrillation potential amplitude in gastrocnemius muscles declined paralleling that in humans. By the end of the study, type I fibers had lost almost half of their initial diameter and type II fibers had atrophied more than twice this amount. Fibrillation potential amplitude may be useful in estimating the time post nerve injury and appears to correlate with the surface area and fiber diameter of a type I muscle fiber.     

Macroelectromyography in progressive post-polio muscular atrophy

A prospective 2-year clinical and macro-EMG follow up was completed in 30 post-polio survivors (19 women and 11 men, aged from 46 to 62 years). The median macro-MUPs amplitudes from either biceps brachii or tibial anterior muscles were estimated. A decrease in muscle strength > 1 MRC grade in the tested extremity was found in five patients (fulfilling criteria for progressive post-polio muscle atrophy-PPMA), and 17 post-polio patients complained of new weakness (Including five PPMA subjects). In seven healthy volunteers the changes in the median macro-MUPs amplitudes on serial examination varied from ?18.8 to +22.4%. In 13 clinically stable patients the change in macro-MUPs amplitude over 2 years did not exceed 25% of the initial value, in comparison with nine of 17 patients with new complaints displaying a > 25% change in the macro-MUPs amplitude, with predominant decrease (6 of 9). All five PPMA patients showed a >25% change in the macro-MUPs amplitude with predominant decrease (+ 33, ?27, ?42, ?50 and ?60%). There was a statistically significant difference in the change of the median macro-MUPs amplitudes between PPMA group (n ? 5) and post-polio patients without objective decline in muscle strength (n = 25; p < 0.05; the Mann–Whitney U test). These findings support the hypothesis of the distal degeneration of abnormally enlarged motor units as a cause of PPMA and show the usefulness of serial measurement in the assessment of PPMA.     

Motor function-muscle strength relationship in spinal muscular atrophy

The relationship between motor function and muscle strength in patients with spinal muscular atrophy (SMA) is still controversial. In 120 genetically proven SMA patients, aged 5 years or older, we measured muscle strength in the arms and legs by a hand-held dynamometer, forced vital capacity by a spirometer, and the time needed to walk 10 m, arise from the floor, and climb steps. SMA patients had markedly reduced muscle strength, approximating 20% of that predicted from age- and gender-matched normative data. Knee extensors were the weakest muscles in SMA patients. The young ambulant SMA patients performed better than adults in all the timed tests and had greater muscle strength on knee extension. This study shows a good relationship between motor ability and muscle strength in SMA and confirms that age-related loss of function in SMA is due to loss of muscle strength.     

Electrical stimulation impairs early functional recovery and accentuates skeletal muscle atrophy after sciatic nerve crush injury in rats

Neuromuscular recovery after peripheral nerve lesion depends on the regeneration of severed axons that re‐establish their functional connection with the denervated muscle. The aim of this study was to determine the effects of electrical stimulation (ES) on the neuromuscular recovery after nerve crush injury in rats. Electrical stimulation was carried out on the tibialis anterior (TA) muscle after sciatic nerve crush injury in a rat model. Six ES sessions were administered every other day starting from day 3 postinjury until the end of the experiment (day 14). The sciatic functional index was calculated. Muscle excitability, neural cell adhesion molecule (N‐CAM) expression, and muscle fiber cross‐sectional area (CSA) were accessed from TA muscle. Regenerated sciatic nerves were analyzed by light and confocal microscopy. Both treated (crush+ES) and untreated (crush) groups had their muscle weight and CSA decreased compared with the normal group (P < 0.05). Electrical stimulation accentuated muscle fiber atrophy more in the crush+ES than in the crush group (P < 0.05). N‐CAM expression increased in both crush and crush+ES groups compared with the normal group (P < 0.05). Regenerated nerves revealed no difference between the crush and crush+ES groups. Nevertheless, functional recovery at day 14 post‐injury was significantly lower in crush+ES group compared with the crush group. In addition, the crush+ES group had chronaxie values significantly higher on days 7 and 13 compared with the crush group, which indicates a decrease in muscle excitability in the crush+ES animals. The results of this study do not support a benefit of the tested protocol of ES during the period of motor nerve recovery following injury. Muscle Nerve, 2010     

Randomized controlled trial of strength training in post-polio patients

Many post-polio patients develop new muscle weakness decades after the initial illness. However, its mechanism and treatment are controversial. The purpose of this study was to test the hypotheses that: (1) after strength training, post-polio patients show strength improvement comparable to that seen in the healthy elderly; (2) such training does not have a deleterious effect on motor unit (MU) survival; and (3) part of the strength improvement is due to an increase in voluntary motor drive. After baseline measures including maximum voluntary contraction force, voluntary activation index, motor unit number estimate, and the tetanic tension of the thumb muscles had been determined, 10 post-polio patients with hand involvement were randomized to either the training or control group. The progressive resistance training program consisted of three sets of eight isometric contractions, three times weekly for 12 weeks. Seven healthy elderly were also randomized and trained in a similar manner. Changes in the baseline parameters were monitored once every 4 weeks throughout the training period. The trained post-polio patients showed a significant improvement in their strength (P < 0.05). The magnitude of gain was greater than that seen in the healthy elderly (mean +/- SE, 41 +/- 16% vs. 29 +/- 8%). The training did not adversely affect MU survival and the improvement was largely attributable to an increase in voluntary motor drive. We therefore conclude that moderate intensity strength training is safe and effective in post-polio patients.     

Quantitative muscle ultrasound and quadriceps strength in patients with post‐polio syndrome

Introduction: We investigated whether muscle ultrasound can distinguish muscles affected by post‐polio syndrome (PPS) from healthy muscles and whether severity of ultrasound abnormalities is associated with muscle strength. Methods: Echo intensity, muscle thickness, and isometric strength of the quadriceps muscles were measured in 48 patients with PPS and 12 healthy controls. Results: Patients with PPS had significantly higher echo intensity and lower muscle thickness than healthy controls. In patients, both echo intensity and muscle thickness were associated independently with muscle strength. A combined measure of echo intensity and muscle thickness was more strongly related to muscle strength than either parameter alone. Conclusions: Quantitative ultrasound distinguishes healthy muscles from those affected by PPS, and measures of muscle quality and quantity are associated with muscle strength. Hence, ultrasound could be a useful tool for assessing disease severity and monitoring changes resulting from disease progression or clinical intervention in patients with PPS. Muscle Nerve 51 : 24–29, 2015     

Activity attenuates skeletal muscle fiber damage after ischemia and reperfusion

Introduction: In this investigation we aimed to determine whether: (1) physical activity protects rat skeletal muscle from ischemia/reperfusion (I/R) injury; and (2) continued activity after I/R improves the rate of healing. Methods: Rats were divided into sedentary or active (voluntary wheel running) groups. Active rats ran for 4 weeks before I/R or 4 weeks before plus 4 weeks after I/R. Results: Activity before I/R resulted in 73.2% less muscle damage (Evans blue dye inclusion). Sedentary and active rats had a similar decline in neural‐evoked (～99%) and directly stimulated (～70%) in vivo muscle torque, and a similar reduction in junctophilin 1. Active rats produced 19% and 15% greater neural‐evoked torque compared with sedentary rats at 14 and 28 days postinjury, respectively, although the rate of recovery appeared similar. Conclusions: Activity protects against long‐term muscle damage, but not short‐term neural injury or excitation‐contraction uncoupling. Continued activity neither accelerates nor hinders the rate of functional recovery. Muscle Nerve 52: 640–648, 2015     

Compound muscle action potential and motor function in children with spinal muscular atrophy

Reliable outcome measures that reflect the underlying disease process and correlate with motor function in children with SMA are needed for clinical trials. Maximum ulnar compound muscle action potential (CMAP) data were collected at two visits over a 4–6‐week period in children with SMA types II and III, 2–17 years of age, at four academic centers. Primary functional outcome measures included the Modified Hammersmith Functional Motor Scale (MHFMS) and MHFMS‐Extend. CMAP negative peak amplitude and area showed excellent discrimination between the ambulatory and non‐ambulatory SMA cohorts (ROC = 0.88). CMAP had excellent test–retest reliability (ICC = 0.96–0.97, n = 64) and moderate to strong correlation with the MHFMS and MHFMS‐Extend (r = 0.61–0.73, n = 68, P < 0.001). Maximum ulnar CMAP amplitude and area is a feasible, valid, and reliable outcome measure for use in pediatric multicenter clinical trials in SMA. CMAP correlates well with motor function and has potential value as a relevant surrogate for disease status. Muscle Nerve, 2010