Bone mineral density and muscle strength in young men with mental retardation (With and without Down syndrome)

The objective of this study was to compare the bone mineral density (BMD) o f men with Down syndrome (DS) to otherwise mentally retarded (MR) men and t o investigate whether leg muscle strength of these patients is related to B MD. Two groups with MR (with and without DS) participated in the study, hav ing met the following criteria: similar age, moderate to mild mental retard ation, Tanner stage V of sexual development, similar age of beginning to wa lk, and equal motor activities. The DS group consisted of 8 men 23.9 +/- 4. 2 years, and the MR group without DS consisted of 8 men 23.5 +/- 3.6 years. The two groups were compared with 10 sedentary students of the same age ra nge (25.9 +/- 2.9 years) attending our University. The BMD of the 2(nd) to 4(th) lumbar vertebrae was measured in the PA projection and the mean densi ty was expressed as g/cm(2). The isokinetic muscle strength of the right qu adriceps femoris and hamstrings muscles was measured on a Cybex II isokinet ic dynamometer. The value measured was peak torque at angular velocities at 60, 120, and 300 degrees.sec(-1). The results showed that BMD in DS indivi duals versus young adults (reference group of the scanner) was lower at the 26% level (T-score - 2.66 +/- 0.29) and significantly lower (P = 0.002) th an that of the MR group. Significantly different muscle strength was observ ed between the DS and non-DS MR group (in quadriceps at 300 degrees.s(-1): P < 0.01, at 120 and 60 degrees.s(-1): P < 0.05; in hamstrings at 300 degre es.s(-1): P < 0.05). Higher differences in muscle strength were found betwe en MR and control men, but no significant difference existed in BMD between them. Bivariate correlation showed that quadriceps strength significantly predicted the BMD in the DS patients. Active lifestyle and increased physic al exercise to improve muscular strength should be instituted to avoid the development of osteoporosis in DS patients.