Hand Muscle Strength and Endurance of Individuals with Down Syndrome

Original Article

Austin J Clin Neurol 2020; 7(1): 1137.

Hand Muscle Strength and Endurance of Individuals with Down Syndrome

Wang HY1*, Tang YT2 and Long IM3

¹Department of Medical Research, Kaohsiung Medical University Hospital, Taiwan

²Department of Rehabilitation, Shin Kao Feng Hospital, Taiwan

³Loving Hands Physiotherapy Center, Macau

*Corresponding author: Hui-Yi Wang, Department of Physical Therapy, Kaohsiung Medical University, No. 100, Shih- Chuan 1st Rd, Sanmin District, Kaohsiung, Taiwan

Received: April 28, 2020; Accepted: May 14, 2020; Published: May 21, 2020


Down Syndrome (DS) is a chromosomal disorder. To date, no reports have detailed hand strength and hand endurance of people with DS.

Purpose: To demonstrate strength and endurance characteristics of hand grip and pinch in individuals with DS.

Methods: Forty-eight participants with DS (17.5±4.0 years) and 62 typical peers (17.8±3.7 years) were recruited. A digital dynamometer (MicroFET4) was used to measure voluntary hand force.

Results: The peak grip and pinch strength in DS group were significantly lower than those of the typical group (p<0.01). However, no significant differences in dynamic grip and pinch endurance were found between the groups. DS group exhibited lesser strength reduction on the static hold grip test than that of the typical group.

Conclusions: Our findings reveal that individuals with DS exert weaker hand grip and pinch strength; nevertheless, they may have abilities of executing sustained time to the hand movements.

Keywords: Down syndrome; Muscle strength; Endurance; Grip; Pinch


Down Syndrome (DS) is the most common chromosomal disorder causing psychomotor disabilities in children, adolescents and adults [1-3]. It is well recognized that individuals with DS exhibit insufficient leg muscle strength [4,5]. In recent studies, grip and pinch strength of individuals with DS were reported [6,7]. In addition to hand strength, hand endurance is also worth studying. In daily living, manual tasks involve the ability of repetitive hand movements (dynamic endurance). Also, using hands to carry or sustain objects involve the ability of hand holding (static endurance). To date, no reports have detailed both the hand muscle strength and endurance in individuals with DS. Studying such hand features in DS is crucial to revealing the physical abilities that are unique to individuals with DS. Moreover, it offers important hand function parameters that would be helpful for any considered physical training intervention. The objective of this study was to demonstrate strength and endurance characteristics of hand grip and pinch in individuals with DS.


Participants: Participants with DS were recruited via convenience sampling from four local organizations (three special education schools and a local Down syndrome association). The inclusion criteria included participants who had been diagnosed by a pediatrician with DS, had functional visual and hearing abilities, and could follow instructions to participate in our measurements. The exclusion criterion was that participants had had a history of cardiopulmonary or orthopedic surgery in the last year. Forty-eight individuals (DS group, 28 boys & 20 girls) aged between 12.2 and 24.0 years (mean±SD, 17.5±4.0 years) were recruited. Another group of sixty-two participants (typical group, 38 boys & 24 girls, 12.4~24.0 years old) without any clinical neuro-developmental, orthopedic or cardiopulmonary disorders were selected to match the participants with DS on age and gender.

Materials used and three hand tests

A computerized system incorporating a digital hand dynamometer (model TBS-2000 MicroFET-4, Hoggan Scientific, LLC, UT) was used. MicroFET-4 has been reported showing high test-retest reliability and low technical error of measuring hand strength [8,9]. Sensors of the MicroFET-4 include a cylindrical handle for transducing grip strength and a paddle portion for gauging pinch strength. Force output via the sensors is transmitted and recorded by using the computer system software. The device measured in pounds. Measurement precision was in 0.1 pound increments. Three different tests were carried out for all the participants. The order of the tests was: a series of 6-repetition grips, a 15-second static hold grip and a series of 4-repetition pinches. In our pilot testing, performing 6 repetitions of grips and 4 repetitions of pinches were found as appropriate to test individuals with DS without inducing their uncomfortable muscle soreness.

Procedure of hand grip measurement

Participants were instructed to sit in a standardized, stable sitting position in a chair with back support, with hips flexed at approximately 90 degrees, and feet placed flat on the floor. Their elbows were slightly forward of the hips, and were flexed to produce an approximate 90 degrees angle with the forearms in a neutral position. The wrists were positioned between 0 and 30 degrees dorsiflexion. Each participant was instructed to clench the cylindrical handle (cylindrical circumference: 14 cm) of the MicroFET-4. Hand grip was performed by consecutive trial alternately on right and left hands to complete 6 trials on each hand. For each trial, participants were verbally encouraged to grip as strong as possible, and held the grip for about 3 seconds in order to generate a peak contraction. A short rest for approximately 5 seconds was given between trials. The peak of each contraction was recorded. For static hold grips, participants clenched the dynamometer handle to conduct a 15-second grip. Participants were verbally encouraged to sustain maximal contraction. Each hand performed once. By using the computer software of the MicroFET-4 system, the value of fatigue slope after each hold grip was displayed. Fatigue slope indicates the degree to which muscle strength leans downward during muscle contraction. A larger negative value of the fatigue slope represents a poorer static hand endurance.

Procedure of hand pinch measurement

Participants were instructed to sit in the chair with shoulders abducted between 30 and 45 degrees. Their elbows were flexed in an approximate 90 degrees with the forearms in a pronated position. They pinched the paddle transducer of the dynamometer by using the pads of thumb and index finger, and were verbally encouraged to maintain this for about 3 seconds to generate peak contraction. The testing was performed alternately on both hands until 4 trials completed on each side. A peak value of each contraction was recorded.

Data analysis

Statistical analyses were conducted using IBM SPSS V19. Descriptive statistics were applied to all analyzed variables. Independent sample t-test was applied to compare variables between the two groups. In order to understand any significant change of peak value during the period of repetitive contraction, paired t-test was used to examine the mean peak strength of the first half of the repetitive contractions (i.e. the first 3 grips, the first 2 pinches) and that of the second half (i.e. the last 3 grips, the last 2 pinches). To estimate the dynamic grip and pinch endurance, a fatigue index was used as a measure of endurance flowing the method of Nicolay, et al. [10] and White et al. [11] This index is the percentage of [peak strength of the first repetition minus the last repetition] relative to the peak strength of the first repetition. A larger fatigue index indicates a greater dynamic fatigue. A significance level of p <0.05 was used for all analyses.


Table 1 displays the data of participants’ age, body height and body weight by groups and also by gender.