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Open Access Research article

Strength characterization of knee flexor and extensor muscles in Prader-Willi and obese patients

Paolo Capodaglio1*, Luca Vismara1, Francesco Menegoni12, Gabriele Baccalaro1, Manuela Galli2 and Graziano Grugni3

Author Affiliations

1 Orthopaedic Rehabilitation Unit and Clinical Lab for Gait Analysis and Posture, Ospedale San Giuseppe, Istituto Auxologico Italiano IRCCS, Piancavallo (Verbania), Italy

2 Bioengineering Department, Politecnico di Milano, Milano, Italy

3 Division of Auxology, Ospedale San Giuseppe, Istituto Auxologico Italiano IRCCS, Piancavallo (Verbania), Italy

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BMC Musculoskeletal Disorders 2009, 10:47  doi:10.1186/1471-2474-10-47

Published: 6 May 2009

Abstract

Background

despite evidence of an obesity-related disability, there is a lack of objective muscle functional data in overweight subjects. Only few studies provide instrumental strength measurements in non-syndromal obesity, whereas no data about Prader-Willi syndrome (PWS) are reported. The aim of our study was to characterize the lower limb muscle function of patients affected by PWS as compared to non-syndromal obesity and normal-weight subjects.

Methods

We enrolled 20 obese (O) females (age: 29.1 ± 6.5 years; BMI: 38.1 ± 3.1), 6 PWS females (age: 27.2 ± 4.9 years; BMI: 45.8 ± 4.4) and 14 healthy normal-weight (H) females (age: 30.1 ± 4.7 years; BMI: 21 ± 1.6). Isokinetic strength during knee flexion and extension in both lower limbs at the fixed angular velocities of 60°/s, 180°/s, 240°/s was measured with a Cybex Norm dynamometer.

Results

the H, O and PWS populations appear to be clearly stratified with regard to muscle strength.: PWS showed the lowest absolute peak torque (PT) for knee flexor and extensor muscles as compared to O (-55%) and H (-47%) (P = 0.00001). O showed significantly higher strength values than H as regard to knee extension only (P = 0.0014). When strength data were normalised by body weight, PWS showed a 50% and a 70% reduction in PT as compared to O and H, respectively. Knee flexors strength values were on average half of those reported for extension in all of the three populations.

Conclusion

the novel aspect of our study is the determination of objective measures of muscle strength in PWS and the comparison with O and H patients. The objective characterization of muscle function performed in this study provides baseline and outcome measures that may quantify specific strength deficits amendable with tailored rehabilitation programs and monitor effectiveness of treatments.