15 Introduction Neurofibromatosis Type 1 (NF1) is a common autosomal- dominant disease (1:3000) with a wide variety of clinical fea- tures. Fine motor coordination deficits have been demon- strated in NF1 1 . Muscular hipotony was clinically suspected in many of the NF1 patients attended at the Neurofibromatosis Reference Center 2 . However, muscular force has not been quantified in NF1 based on an extensive review of the literature from 1956 to 2008. A previous study using peripheral quantitative tomography showed decreased muscle cross-sectional area plus decreased bone strength in NF1 patients but the muscular force was not measured 3 . The handgrip force test measures maximal voluntary muscular force (F max ) and it has successfully been used to evaluate long-term human disability 4 . It is well known that muscular force is correlated to muscle and body dimensions, which varies between males and females, as well as with habitual physical activities and trough out the life. To allow compar- isons between such different individuals, the handgrip F max must be divided by the forearm cross sectional area 5 . Based on clinical observations we hypothesized that F max measured by handgrip test would be reduced in NF1 patients. Material and methods The Federal University of Minas Gerais Ethical Committee approved this study (# 570/07). The maximal vol- untary muscular force (F max ) was measured in the first 21 NF1 patients and 21 healthy controls. The NF1 individuals were 9 males and 12 females, aged from 7 to 60 years old, without acute healthy problems and physically sedentary. The patients enrolled in this study were volunteers recruited from the annual routine examination in the Neurofibromatosis Reference Center along the period of October and November 2007. The healthy control group was matched by sex, age and physical activity and it was formed by students and university's workers. The diagnosis of NF1 was estab- lished according to the National Institute of Health consen- sus criteria 6 and they presented the common clinical features J Musculoskelet Neuronal Interact 2009; 9(1):15-17 Muscular force is reduced in neurofibromatosis type 1 J.F. Souza 1 , R.L.F. Passos 2 , A.C.M. Guedes 1 , N.A. Rezende 1 , L.O.C. Rodrigues 1 1 Neurofibromatosis Outpatient Reference Center, School of Medicine; 2 Sports Sciences Pos Graduated Program, School of Physical Education Physiotherapy and Ocupational Therapy, Federal University of Minas Gerais, Brazil Abstract Objectives: To measure muscular force in neurofibromatosis type 1 (NF1) patients. Methods: The maximal voluntary mus- cular force (F max ) was measured in the first 21 volunteer patients without acute health problems at the routine annual exami- nation in the Neurofibromatosis Outpatient Reference Center during October-November (2007). The NF1 individuals were 9 males and 12 females, aged from 7 to 60 years and physically sedentary. The healthy control group was 21 healthy subjects matched to NF1 group by age, sex and physical activity. A handgrip test instrument was used to measure maximal force. To allow comparisons between physically different patients, forearm circumference (cm) was measured with a tape and forearm cross sectional area was derived to express the force per unit of forearm area. Data were compared using a t Student test (P<0.05). Results: The mean F max of NF1 male (260±136 N) and NF1 female (217±76 N) were lower than expected for their sex and age. Healthy men showed greater F area (9.8±3.2 N.cm -2 ) than NF1 men (5.7±2.6 N.cm -2 ) and healthy women (6.7±1.6 N.cm -2 ) showed greater F area than NF1 females (5.7±1.9 N.cm -2 ). Conclusion: Maximal voluntary muscle force was reduced in NF1 patients. Keywords: Neurofibromatosis Type 1, Muscular Force and Handgrip Original Article Hylonome The authors have no conflict of interest. Corresponding author: Luiz Oswaldo Carneiro Rodrigues, M.D., Ph.D., Rua Roberto. L. Aroeira 40 - 31710-570 - Belo Horizonte, Minas Gerais, Brazil E-mail: lor@ufmg.br Accepted 27 January 2009