The optimal joint angle for adductor pollicis force production in men and women

Adductor pollicis muscle thickness: a promising anthropometric parameter for patients with chronic renal failure

INTRODUCTION

Protein-calorie malnutrition is a prevalent disorder in chronic renal failure (CRF) and a major risk factor for increased mortality in hemodialysis (HD) patients. Although many methods have been used to assess malnutrition in CRF, the role of adductor pollicis muscle thickness (APMt) is not established yet.

AIMS

This study aimed to analyze the APMt in HD patients and to investigate the correlation between APMt and conventional anthropometric, laboratory, and bioelectrical impedance markers, as well as its association with mortality/morbidity in a period of 12 months of follow-up.

SUBJECTS AND METHODS

The study included 143 HD patients from a single facility. After dialysis, the dry weight, height, mid-arm circumference, triceps skinfold thickness, and APMt were measured. Subsequently, the body mass index, percentage of standard body weight, the mid-arm muscle circumference, and the mid-arm muscle area were calculated. Blood counts were performed for hemoglobin, creatinine, and albumin. Patients were also submitted to a single-frequency tetrapolar bioimpedance test for measuring resistance, reactance, phase angle, and percentage of body cell mass. The correlation between APMt and anthropometric, laboratory, and bioelectrical impedance parameters was calculated using Pearson's linear correlation. Multiple linear regression analysis was used to select independent risk factors to death and hospitalizations in 6 and 12 months of follow-up, among parameters selected by univariate analysis.

RESULTS

Patients were aged 52.2 ± 16.6 years (20 to 83 years) on average, 58% were men, and mean dialysis vintage was 5.27 ± 5.12 years. APMt was 11.85 ± 1.63 mm (men, 12.34 ± 1.53; women, 11.19 ± 1.51; P < .0001). APMt was positively correlated with body mass index (r = 0.37; P < .0001), mid-arm circumference (r = 0.437; P < .0001), mid-arm muscle circumference (r = 0.494; P < .0001), mid-arm muscle area (r = 0.449; P < .0001), percentage of standard body weight (r = 0.355; P = .000), creatinine (r = 0.230; P = .006), albumin (r = 0.207; P = .013), percentage of body cell mass (r = 0.293; P = .000), and phase angle (r = 0.402; P < .0001), and negatively correlated with resistance (r = -0.403; P < .0001). The APMt ≤10.6 mm was associated with a 3.3 times greater risk of hospitalization within 6 months of follow-up (OR = 3.3, 95% CI: 1.13 to 9.66; P = .029) compared with patients with an APMt >10.6 mm. The APMt was not associated with risk of death at 6 and 12 months or hospitalization within 12 months of follow-up.

CONCLUSION

This is the first study testing APMt as an anthropometric marker in HD patients. The parameter is easy to measure and does not seem to be significantly affected by variations in hydration status. The parameter was significantly correlated with markers reflecting the condition of the muscle compartment, but not with parameters estimating the fat mass. The determination of an APMt cutoff point for malnutrition in patients with CRF and its correlation with morbidity and mortality will require further investigation in clinical studies.

Progressive suppression of intracortical inhibition during graded isometric contraction of a hand muscle is not influenced by hand preference

GABAergic intracortical inhibition (ICI) in human motor cortex (M1) assists fractionated activation of muscles, and it has been suggested that hemispheric differences in ICI may contribute to hand preference. Previous studies of this issue have all been conducted at rest, with conflicting results. Testing during voluntary activation may reveal functionally relevant differences. In normal subjects, we assessed (1) operation of ICI circuits during selective activation of an intrinsic hand muscle at different forces, and (2) whether this differs between right and left hemispheres. Surface EMG was recorded bilaterally from abductor pollicis brevis (APB), first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles in eleven right-handed subjects. A circular coil applied paired transcranial magnetic stimulation (TMS) with posteriorly directed current in the brain. Conditioning intensity was 0.8 x active threshold and interstimulus interval was 3 ms. TMS was applied to right or left M1 while subjects were at rest or performing isometric thumb abduction at different forces (0.5, 1, 2, 3, 5 and 10 N) with the contralateral hand. Conditioning TMS was less effective at suppressing the muscle evoked potential in APB during 2-10 N thumb abduction (P < 0.0001) versus rest, but not with lower target forces (0.5, 1 N). Conditioning TMS was less effective for FDI and ADM only during 10 N thumb abduction. We conclude that differential modulation of ICI in M1 during selective muscle activation is a function of target isometric force level. At low forces (<5% MVC), ICI is not modulated for the corticospinal neurons controlling the active or inactive muscles. There is a progressive reduction of ICI effects on corticospinal neurons at higher forces, which is largely restricted to corticospinal neurons controlling the muscle targeted for activation over the range of forces tested (up to approximately 25% MVC). The pattern of ICI modulation with selective voluntary muscle contraction was similar in left and right hemispheres during this relatively simple static task. If hemispheric differences in operation of M1 ICI circuits contribute to hand preference, a more challenging finger movement protocol may be needed to demonstrate this asymmetry.

Thumb force deficit after lower median nerve block

Purpose

The purpose of this study was to characterize thumb motor dysfunction resulting from simulated lower median nerve lesions at the wrist.

Methods

Bupivacaine hydrochloride was injected into the carpal tunnel of six healthy subjects to locally anesthetize the median nerve. Motor function was subsequently evaluated by measuring maximal force production in all directions within the transverse plane perpendicular to the longitudinal axis of the thumb. Force envelopes were constructed using these measured multidirectional forces.

Results

Blockage of the median nerve resulted in decreased force magnitudes and thus smaller force envelopes. The average force decrease around the force envelope was 27.9%. A maximum decrease of 42.4% occurred in a direction combining abduction and slight flexion, while a minimum decrease of 10.5% occurred in a direction combining adduction and slight flexion. Relative decreases in adduction, extension, abduction, and flexion were 17.3%, 21.2%, 41.2% and 33.5%, respectively. Areas enclosed by pre- and post-block force envelopes were 20628 ± 7747 N.N, and 10700 ± 4474 N.N, respectively, representing an average decrease of 48.1%. Relative decreases in the adduction, extension, abduction, and flexion quadrant areas were 31.5%, 42.3%, 60.9%, and 52.3%, respectively.

Conclusion

Lower median nerve lesion, simulated by a nerve block at the wrist, compromise normal motor function of the thumb. A median nerve block results in force deficits in all directions, with the most severe impairment in abduction and flexion. From our results, such a means of motor function assessment can potentially be applied to functionally evaluate peripheral neuropathies.

Circumferential force production of the thumb

We developed an apparatus to measure maximal continuous circumferential forces of a digit in the transverse plane that is perpendicular to the longitudinal axis. Subjects with asymptomatic hands were asked to produce maximal forces in all directions at the proximal phalanx of the thumb. The force components during circumferential trials were used to construct a force envelope for each subject. The force envelope enlarged as the number of trials increased, and converged to a stable pattern after several trials. The shape of the force envelope was asymmetric and oblique, skewed towards the flexion/adduction direction. Maximal force (112.1 +/- 14.8 N) was generated in the direction combining flexion and adduction. The lowest force produced was only 50.3% of the maximal force in a direction combining extension and abduction. The forces in the direction of adduction, extension, abduction, and flexion were 60.1%, 61.9%, 51.5%, and 92.9% of the maximal force, respectively. The forces generated by circumferential exertions were comparable to the forces by focused directional exertions except in the flexion direction. Our methods have the potential to identify deviations from the normative force output pattern and help detect underlying impairments resulting from neuromuscular disorders.

A comparison of adductor pollicis fatigue in older men and women

Sex differences in fatigue resistance of the adductor pollicis (AP) muscle were studied in 24 older adults who were divided into three groups: 12 older men (69.8 +/- 4.60 years), 6 older women not on hormone replacement therapy (HRT) (70.2 +/- 4.02 years), and 6 older women on HRT (68.7 +/- 6.47 years). Fatigue in the AP muscle was induced using an intermittent (5 s contraction, 5 s rest) submaximal voluntary contraction (50% of maximal voluntary contraction (MVC)) protocol, which was continued until exhaustion (i.e., when subjects could either no longer maintain a 5-s contraction at 50% MVC or when the MVC was deemed to be lower than the target force). There was no effect of HRT on MVC or time to fatigue (TTF); therefore, the older women were pooled as one subject group. At baseline, men were stronger than women for MVC (75.9 +/- 18.8 N in men vs. 56.8 +/- 10.0 N in women; P < 0.05) and evoked twitch force (7.3 +/- 1.7 N in men vs. 5.2 +/- 0.8 N in women; P < 0.05). There was no difference in TTF between men and women (14.77 +/- 7.06 min in men vs. 11.53 +/- 4.91 min in women; P > 0.20), nor was there a significant relationship between baseline muscle force and TTF (r = 0.14). There was also no difference in the pattern of fatigue and recovery between the men and women. These results suggest that there is no difference in endurance or fatigue characteristics of the AP muscle in men and women over the age of 65 years, and that baseline muscle force does not predict fatigue resistance in this muscle.

The thickness of the adductor pollicis muscle reflects the muscle compartment and may be used as a new anthropometric parameter for nutritional assessment

PURPOSE OF REVIEW

Contraction of the adductor pollicis muscle after electrical stimulation (electromyogram) or dynamometry (hand-grip tests) has been evaluated in a variety of clinical conditions as a parameter to assess nutritional status. However, adductor pollicis muscle thickness has not been investigated as an anthropometric parameter.

RECENT FINDINGS

Prolonged immobilization and non-use of lower and upper limb muscles causes atrophy. Adductor pollicis muscle function is normal in patients with stable chronic obstructive pulmonary disease and multiple sclerosis, whereas the musculature of lower limbs suffers more pronounced functional alterations. Structure and function are relatively preserved in upper limb muscles, probably because of the maintenance of some daily activities involving the arms. Inactivity as a result of a reduction in daily activities is probably the driving factor for these changes. Forearm immobilization for 21 days caused no significant change in muscle morphology, but caused a deterioration in muscle function. Virtually all routinely developed activities requiring opposition of the thumb muscle and repetitive exercise of one muscle group for a given period of time maintain muscle size and function. Apathy is often observed as malnutrition progresses, reducing daily working activity and aggravating adductor pollicis muscle loss besides the muscular catabolism caused by disease.

SUMMARY

This study provides the first estimates of adductor pollicis muscle thickness in normal healthy individuals. The adductor pollicis muscle has a positive correlation with anthropometric variables that estimate muscle mass, but fails to correlate with parameters that estimate fat mass. This measurement is now being evaluated as an anthropometric parameter in clinical studies.

The effect of age and gender on the relative fatigability of the human adductor pollicis muscle

The purpose of this study was to examine the relative influence of such factors as age, gender, and absolute force on the fatiguability of the human adductor pollicis muscle. 12 young males (YM, 25.3 ± 2.1 y), 12 young females (YF, 23.5 ± 2.1 y), 12 older males (OM, 71.7 ± 5.6 y) and 12 older females (OF, 69.5 ± 4.6 y) participated. Three minutes of intermittent (5 s contraction, 2 s rest) maximal voluntary contractions (MVC) were used to fatigue the adductor pollicis muscle; the ulnar nerve was also stimulated in each 2 s rest period to evoke a maximal twitch. Males were stronger than females in both voluntary and evoked force (PT) in the young age group (MVC: YM, 10.0 ± 2.7 kg vs. YF, 6.6 ± 1.1 kg, P < 0.05) (PT: YM, 0.99 ± 0.21 kg vs. YF, 0.71 ± 0.12 kg, P < 0.05). In the older adults, however, males were stronger only in the evoked twitch (OM, 0.73 ± 0.24 kg vs. OF, 0.48 ± 0.07 kg, P < 0.05). There was no significant effect of gender or absolute muscle force on relative fatigability; the only variable found to significantly affect fatigability was age. Older adults were significantly less fatigable than young adults as indicated by the voluntary fatigue index (FI) (percentage of force reduction from baseline; FI-young, 40.2 ± 12.6% vs. FI-old, 25.2 ± 12.3%). This age effect, however, was more prominent in males than females (FI-YM, 44.7 ± 10.5% vs. FI-OM, 24.2 ± 10.7%, P < 0.01; FI-YF, 37.8 ± 14.1% vs. FI-OF, 26.3 ± 14.5%, P = 0.13). In conclusion, age was found to be the strongest single predictor of fatigability during short duration, intermittent exercise in human adductor pollicis muscle.Key words: neuromuscular fatigue, gender, age, muscle membrane excitability, absolute force.