Mechanical and myoelectric manifestations of fatigue in subjects with anorexia nervosa

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Abstract

Purpose

Aim of this work is to compare mechanical and myoelectric manifestations of fatigue during an isometric contraction at 80% of maximal voluntary contraction (MVC) in a population of eight anorexic female patients (AN: 24.9 ± 6.5 years, mean ± SD) with respect to a group of seven healthy female subjects (CO: 30.0 ± 6.6 years, mean ± SD).

Methods

sEMG signals were recorded, using a linear electrode array (eight channels, 10 mm apart), from vastus lateralis muscle of the dominant side. MVC, endurance time, initial value and rate of change of the EMG variables [conduction velocity (CV), mean power frequency (MNF), average rectified value (ARV)] were studied during the fatiguing contractions.

Results

Absolute and relative (normalized with respect to the body weight) knee torque values and endurance times were found not statistically different between the two groups. Similarly, EMG amplitude initial values and rate of change and MNF initial values were found not significantly different between the two groups. CV initial values and CV rate of change were found greater in healthy than in pathological subjects (AN CV: 3.74 ± 0.86 m/s, CO CV: 4.96 ± 0.64 m/s, p = 0.004; AN CV rate of change: 0.006 ± 0.015 m/s2, CO CV rate of change: −0.006 ± 0.007 m/s2, p = 0.006, mean ± SD). Contrary to expectations MNF rate of changes in the AN group (−0.35 ± 0.16 Hz/s) was found greater than in the CO group (−0.17 ± 0.13 Hz/s, p = 0.004, Mann–Whitney U test, mean ± SD).

Conclusions

CV values and their rate of change were compatible with a predominance of type I fibres (and/or with an hypotrophy of type II fibres) and/or with a lower sub-cutaneous tissue thickness with respect to CO group, as described in the literature with this pathology. The behaviour of MNF during sustained contractions, opposite to that of CV, suggests an altered central control strategy aimed to increase mechanical force output increasing the level of synchronization of motor units. This study confirms the capability of sEMG to assess muscle condition during severe malnutrition suggesting further studies to assess if sEMG can be used to monitor the effect of re-feeding and rehabilitation treatments.

Introduction

Anorexia nervosa (AN) is a severe feeding disorder characterized by prolonged restriction of oral nutrient intake with intentional weight loss associated to morphological, biochemical and physiological changes in many organs (Russell et al., 1983b). A loss of fat free mass (FFM) as well as fat mass (FM) was observed in anorexic patients (up to half with respect to healthy subjects (Polito et al., 1998)). Lean tissue loss (from muscle and from viscera) can be 15–45% of the total decrease in body mass (Heymsfield et al., 1979, Shephard, 1991). Bone mineral density as well as bone mineral content may be lower in subjects with AN (Iacopino et al., 2003, Jacoangeli et al., 2002) than in healthy. It has been shown (Lopes et al., 1982) that malnutrition causes both increase of muscle fatigability and altered pattern of muscle contraction and relaxation. In patients with malnutrition a selective atrophy of type II muscle fibers was observed (Lopes et al., 1982, Slettebo et al., 1984). In vastus lateralis muscle of subjects with AN, the cross-section of slow fiber was found increased of 7% as result of a selective ipertrophy with no evidence of neuropathic alterations (McLoughlin et al., 1998). Data were obtained by muscle biopsies, neurography, muscle strength and endurance tests, and surface electromyography (sEMG) signals recorded during both voluntary and electrically elicited contractions.

Many studies (Kupa et al., 1995, Merletti et al., 2002, Moritani and Muro, 1987, Sadoyama et al., 1988) demonstrated the capability of sEMG to non-invasively assess muscle properties. Others showed that changes in muscular function are more sensitive than changes in body composition in detecting malnutrition and monitoring re-feeding (Russell et al., 1983b) or significant changes in body function during dietary restriction (Russell et al., 1983a).

According to these lines of investigation, a non invasive method to muscular function assessment in subjects with AN was proposed in this work. Mechanical and myoelectric manifestations of fatigue during an isometric fatiguing exercise were compared in anorexic and healthy subjects with the following aims: (a) to verify if a fatiguing isometric test can be carried out with such patients, for which the pathological conditions could represent a pivotal limitation per se; (b) to confirm that AN patients show resistance capacities during endurance exercise even in presence of a marked Body Mass Index (BMI) reduction and muscular hypotrophy; and (c) to provide patients with a feedback of the time course of their muscular performance in relation to modifications of feeding behaviours (since, as described above, functional modifications are faster than body composition adaptations) to integrate clinical evaluations, laboratory analyses, assessment of body composition and energetic metabolism, with a quantitative evaluation of muscular electrophysiology.

Section snippets

Patients

Skeletal muscle function (force and EMG variables) was evaluated in eight severely depleted patients (all females, labeled as AN) with primary anorexia nervosa and in a control group of seven healthy females (labeled as CO). They were recruited by the Nutritional and Endocrinological Unit of Tor Vergata’s General Hospital of Rome. All patients satisfied the diagnostic criteria presented in the official manual for the classification of the psychiatric pathologies (DSMIV, 1994). No regular

Anthropometric results

Body weight was found greater (p < 0.001) in CO (57.1 ± 8.0 kg) than in AN (40.3 ± 5.4 kg). The same was for BMI values: they were found greater (p < 0.001) in CO (20.0 ± 2.0 kg/m2) than in AN (15.5 ± 1.7 kg/m2). Sub-cutaneous tissue thickness was found greater (p = 0.05) in the CO group (8.1 ± 3.0 mm) than in the AN group (4.8 ± 2.7 mm).

Mechanical results

MVC torque values did not significantly differ between the two groups (CO: 90.7 ± 13.1 Nm, AN: 74.1 ± 23.6 Nm, p = 0.18) as well as values normalized with respect to the body weight (AN: 1.87 ±

Mechanical results

No statistically significant differences were found in mechanical results (MVC and endurance) between the two groups. These findings are in agreement with other studies (Shizgal et al., 1986, among others) where it was demonstrated that AN subjects prefer endurance exercise and are able to increase their force level in few weeks of exercise. This behaviour, often clinically observed in AN subjects due to its effect in weight control, can contribute to explain findings above. Moreover, it was

Conclusions

The present work confirms: (a) the possibility to study patients with AN adopting a protocol based on a neuromuscular functional test based on EMG; (b) that AN patients show endurance compatible with a predominance of type I fibres (and/or with an hypotrophy of type II fibres or a fiber type conversion) and (c) a greater MNF rate of change of the vastus lateralis muscle with respect to healthy subjects can be related to an altered central control strategy aimed to increase mechanical force

Acknowledgments

The authors particularly thank Professor I. Caruso, MD (Università di Tor Vergata, Roma, Italy) for his continuous effort in promoting the study of new approaches to the clinical practice based on sEMG techniques, and for providing time and facilities for this study. The authors also thank M. Cereti, MD (Università di Tor Vergata, Roma, Italy) for her huge help in the design and management of the clinical aspects of the protocol; Prof. M. Bollea, MD and A. Jacoangeli, MD (Policlinico di Tor

Giovanni Melchiorri received both MD and PhD degrees in Physical Medicine and Rehabilitation from University of Rome Tor Vergata, Italy. Since 2004 he is Research Assistant Professor at the Faculty of Medicine, teaching at the course of Sport Science at the same University. His research focuses on functional evaluation in sport and rehabilitation medicine. Clinical activity is with Don Carlo Gnocchi Foundation rehabilitation center in Rome. Currently he is interested in myoelectric

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    Giovanni Melchiorri received both MD and PhD degrees in Physical Medicine and Rehabilitation from University of Rome Tor Vergata, Italy. Since 2004 he is Research Assistant Professor at the Faculty of Medicine, teaching at the course of Sport Science at the same University. His research focuses on functional evaluation in sport and rehabilitation medicine. Clinical activity is with Don Carlo Gnocchi Foundation rehabilitation center in Rome. Currently he is interested in myoelectric manifestations of muscle fatigue assessed by surface EMG in the fields of sport and orthopaedic rehabilitation.

    Alberto Rainoldi was born in Torino, Italy and graduated in Physics (1991) from Torino University. He obtained the PhD in Physical Medicine and Rehabilitation (2002) at the Faculty of Medicine, Università di Roma ”Tor Vergata”, Italy. Since 1996 he has been with Politecnico di Torino, where his research activity is focused on: the assessment of proper methodologies useful to increase the standardization and the repeatability of EMG measures, allowing their clinical use; the feasibility study of a technique of muscle fiber type estimation based on surface EMG; the assessment of EMG signal modification in different clinical pathologies. He is also a scientific consultant of the S. Maugeri Foundation (Pavia, Italy) for the research projects in the field of Muscle Fatigue. Since 2004 he is a professor at the Motor Science School of the University of Turin, Italy where he teaches the course of “Research Methodology”. Since 2006 he leads the Research Center of the same School. He is member of the Editorial Board of the Journal of Electromyography and Kinesiology.

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