ISOKINETIC KNEE MUSCLE STRENGTH OF

0 downloads 0 Views 294KB Size Report
Binet Intelligence Scale (Terman & Merrill, 1960; Thornfie, Hagen, & Sat- tler, 1985). The subjects of both groups came from the same types of background.
Percepfzraland Motor Skills, 1999,88,849-855. O Perceptual and Motor Slulls 1999

ISOKINETIC KNEE MUSCLE STRENGTH OF INDTVIDUALS WITH MENTAL RETARDATION, A COMPARATIVE STUDY ' NICKOLETTA ANGELOPOULOU, VASSILIS T S I A W S , KOSMAS CHRISTOULAS, DIMITRIOS KOKARIDAS. KONSTANTINOS MANDROUKAS Ergophysiology Loboratory Department of Physical Edzrcation and Sport Science Aristotle Uniuenity of Tbersalorriki Sz~m,na~.-The purpose of this study was to assess differences in isolunetic muscle torque in the knee among mentally retarded individuals with Down syndrome, mentally retarded individuals without Down syndrome, and sedentary subjects without mental retardation (12s of 7, 8, and 12, respectively). Subjects performed strength tests to knee extension and flexion on a Cybex I1 i s o h e t i c dynamometer. The measure was peak corque at angular velocjties of 60, 120, and 300 degreedsec. For the Mentally Retarded subjects with and without Down syndrome, the test was performed on two separate days 24 hr. apart. For Sedentary subiects, testing was performed on one day. Their scores indicated significantly higher values of torque than the two other groups. Also, subjects with Down syndrome had inferior muscle torque of lower extremities than peers in the Mentally Retarded Group.

Down syndrome or trisomy 21 is the most common genetic cause of developmental disabhty and is characterised by mental retardation and associated medical and musculoskeletal dtsorders (Hayes & Batshaw, 1993). Individuals with Down syndrome and mentally disabled individuals in general have been reported to possess lower physical fitness than the nonretarded population (Kerr & Hughes, 1987) as children (Moon & Renzaglia, 1982) and as adults (Reid, Montgomery, & Seidl, 1985). Furthermore, they have lower motor ability than persons with normal intelhgence (Shephard, 1994). In general, mentally retarded individuals, with and without Down syndrome, may be clumsy and awkward and ~erforrnless ~ r o f i c i e n t lthan ~ their nonretarded peers on measurements of balance, directionality, spatial relationship, laterality, and muscle strength (Cooke, 1984; Auxter & Pyfer, 1989, pp. 192208). The physical features and physiological ddferences between individuals with Down syndrome and other retarded individuals, however, place subjects with Down syndrome at a disadvantage in performing physical activities (Pitetti, C h s t e i n , Mays, & Barrett, 1992). Hypotonia and joint hypermobility are universal findings in infants and young children with Down syndrome (Hayes & Batshaw, 19931, which affect the voluntary control of muscles 'Please address correspondence to N. Angelopoulou, M.D., Ph.D., Special Education, 5 Omirou Street, Panorama 55236, Thessaloniki, Greece.

850

N. ANGELOPOULOU. E T a .

(Dyer, Gunn, Rauh, & Berry, 1990) and delay the development of gross motor skdls (Reid, et al., 1985; Pitetti, et a/., 1992). Researchers have found a significant negative correlation benveen hypotonia and muscle strength (Morris, Vaughan, & Vaccaro, 1982; AngelopouIOU-Sakadami, Giangoudaki, Bouli-Kalahani, & Hajisevastou-Loukldou, 1995). Consistent with the above findings, researchers have shown that subjects with Down syndrome have inferior muscle torque of lower extremities than mentally retarded peers without Down syndrome (Pitetti, et al., 1992; Cioni, Cocilovo, Di Pasquale, Araujo, Siqueira, & Bianco, 1994). Also, although there is difficulty in applying accepted protocols of the general population to persons with mental retardation (Reid, et a/., 1985), the assessment of muscle torque on mentally disabled subjects including persons with Down syndrome has identified these individuals as possessing capacities inferior to those of nonmentally retarded peers (Montgomery, Reid, & Seidl, 1988; Shephard, 1994). The necessity for the social and professional integration of the mentally retarded individuals (Schmidt-Gotz, Doll-Tepper, & Lienert, 1994) has led to recent studies focusing on the assessment of muscular strength. These have shown that the use of isolunetic dynamometry in obtaining quantitative measures of muscle strength is reliable both for nonretarded and retarded individuals (Pitetti, et al., 1992; Suomi, Surburg, & Lecius, 1993; Cioni, et al., 1994; Zakas, Mandroukas, Vamvakouhs, Christoulas, & Angelopoulou, 1995). The purpose of this study was to compare isolunetic muscle torque of lower extremities of mentally retarded individuals with Down syndrome, mentally retarded individuals without Down syndrome, and sedentary subjects without mental retardation to assess any differences between them.

Subjects

Seven young adults with Down syndrome and moderate to mild mental retardation (1Q range 45 to 60) and eight non-Down syndrome individuals with mental retardation (IQ range 50 to 65) participated. The Intelligence Quotient of the individuals had been previously estimated on the StanfordBinet Intelligence Scale (Terman & Merrill, 1960; T h o r n f i e , Hagen, & Sattler, 1985). The subjects of both groups came from the same types of background (middle-class famdies), were male and were similar in age (mean age 19.0 4.0 yr. and 20.3 f 2.4 for Down syndrome and Mentally Retarded groups, respectively). All subjects were living with their parents and were attending schools for specific vocations with lessons that involved light physical activity for 4 or 5 hours, five days per week.

+

ISOKINETIC MUSCLE TORQUE IN K N E E

85 1

All participating

mentally retarded individuals were apparently healthy with no orthopaedic impairments that could interfere with testing protocols. Further, they did not manifest sensory impairments, and they were capable of understanding verbal and visual directions. Regarding the mentally retarded individuals without Down syndrome, the evaluation of their disabhty took place in pediatric clinics of the university during their infancy or childhood. The etiology of retardation was prematurity o r identifiable. There was n o chromosomal abnormality or any anatomical disorder in the brain detected by CAT scan. The two groups of mentally retarded individuals were compared with 12 male sedentary subjects without mental retardation (mean age 23.9 f 5.7 yr.).

Procedure All subjects were informed of the purpose of the test and its procedures. In addition, an orientation session was provided to the Mentally Disabled and Down Syndrome groups, one day prior to the actual testing sessions. During this session, written instructions concerning the test procedures and a demonstration of the test were provided the mentally retarded subjects and their mothers. After the demonstration, the subjects performed a number of trials to familiarise themselves with the test procedures and the equipment. The peak torque values of knee extension and flexion were measured from the right lower extremity. Testing was performed on a Cybex I1 isokinetic dynamometer (Lumex Inc., Ronkonkoma, NY 11779). The value measured was peak torque at angular velocities at 60, 120, and 300". set.-'. For the subjects who were mentally disabled, testing was performed on two separate days 24 hours apart, but n o significant differences were found in peak torque values between the two test days. The testing on two different days served the purpose of not underestimating the true ability of these mentally disabled individuals by taking into account that subjects with mental retardation may have difficulty in understanding the need for maximal effort (Fernhall, Tymeson, & Webster, 1988). Furthermore, it is in agreement with previous studies (Pitetti, 1990; Pitetti, et al., 1992), which reliably measured isokinetic torque of adults who were mentally disabled. For the subjects without mental retardation the test was performed only once, with 5 min. of preluninary testing. Prior to testing, all subjects underwent a 6-min. warm-up period on a cycle ergometer. After the warm-up period, the subjects sat on the chair of the dynamometer, with stabilization straps at the trunk, thigh, and tibia to prevent extraneous joint movement. The knee to be tested was positioned at 90" of flexion (On=fully extended knee) to align the axis of the dynamome-

852

N.ANGELOPOULOU, ET AL

ter lever arm with the distal point of the lateral femoral condyle. Subjects were instructed to luck and bend the leg as hard and as fast as possible through a complete range of motion. Verbal encouragement was given during every trial. Subjects were instructed to hold their arms comfortably across the chest to ease knee joint flexion and extension movements. Special attention was paid to the instruction to exert each contraction maximally over the full range of motion. Gravitational torque resulting from the weight of the leg and the Cybex level arm was assessed individually by allowing the subject's leg and level arm in full extension (0" horizontally). In this position, the machine was at 0" and the leg was free. When the leg was stabilized in full extension the gravitational torque was registered on the computer. Peak torque measurements were corrected for the effects of gravity. Three test repetitions with maximal effort were carried out at each angular velocity and the highest peak torque value (Newton-meters) was used. A 30-sec. rest was taken between trials, and a 60-sec. rest between rneasurernents of velocity.

Statistical Analysis Means and standard deviations or means with 95% confidence interval were calculated for all variables (age, height, body mass, IQ, peak torque of ¶uadriceps and hamstrings). Analysis of variance was used to test mean differences between the groups. The differences were located by the Scheffi: post hoc test. RESULTS The physiological characteristics, the intelligence quotient, and the peak torque of quadriceps and hamstrings of the subjects are shown in Table 1. N o significant differences were found between the Mentally Disabled and Sedentary groups in age, height, and weight but were present between the Down Syndrome and the two other groups. A small stature is one of the most common physical features of subjects with Down syndrome (Cronk, Chumlea, & Roche, 1988).As a consequence, the sedentary and mentally &sabled individuals in this study were taller and heavier than Down syndrome subjects. There was no significant difference in terms of IQ between the two mentally retarded groups (Table 1). At all angular velocities, the peak torque of quadriceps of the Sedentary group was significantly higher than the peak torque of the Mentally Disabled group. Ln addition, the peak torque of the quadriceps was significantly higher in the Mentally Disabled group than the Down Syndrome group (Table 1).

The peak corque ior the hamstrings of the Sedentary group was significantly higher than the peak torque of both mentally retarded groups. Furthermore, the peak torque for [he hamstrings was higher in the case of the

853

ISOKINETIC MUSCLE TORQUE IN KNEE TABLE 1 CHARACTERISTICS A N D PUK TORQUE (N-M)O F PHYSIOLOGICAL QUADRICEPS A N D HAMSTRING MUSCLES I N ALLGROUPS Variable

Down Syndrome n=7

M ilpc yr.

SD

19.0' 4 .O 1 . 5 ~ ~ 5.4 57.1dc 5.8 50 6

tlclghr, m Body Mass, kg IQ Peak Torque, N-rn Quadriceps 6O0/sec. 9 6 . 3 f ~ 0 . 0 12O0/sec. 74.0" 8.7 3OO0/sec. 41.4'"' 4.5 Harns~r~ng. 6OS/sec. 57.6@ 6.4 12O0/sec. 43.7qr 5.1 300m/sec. 21.9" 2.2 < ,01, cdefshliMmn~qrs[u~ < ,001. <