Physical Therapy in Sport xxx (2012) 1e5

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Original research

Timing perception and motor coordination on rope jumping in children with attention deficit hyperactivity disorder Ying-Yi Chen a, Lih-Jiun Liaw b, Jing-Min Liang a, Wei-Tso Hung a, Lan-Yuen Guo a, Wen-Lan Wu a, * a b

Department of Sports Medicine, Kaohsiung Medical University, 100, Shih-Chuan 1st Rd., Kaohsiung City, 80708, Taiwan Department of Physical Therapy, Kaohsiung Medical University, Taiwan

a r t i c l e i n f o

a b s t r a c t

Article history: Received 14 June 2011 Received in revised form 22 February 2012 Accepted 6 March 2012

Objectives: To evaluate timing perception ability and motor coordination in children with ADHD (Attention Deficit Hyperactivity Disorder) while rope jumping at different rates. Design and setting: Rope jumping at (1) a constant tempo of 100 for 15 s (RJ-C) and (2) two randomly permutated tempos (80, 100, or 120) for 15 s (RJ-V). Main Outcome Measures: The “timing variation while jumping”, “timing variation while whirling”, and “hand-foot deviation time” in each rope jumping cycle were recorded, to assess the time estimation ability. Participants: 10 children with ADHD (9.65
1.27 years) and 10 children without ADHD (9.93
1.54 years) were recruited. Results: The ADHD group showed greater variation in time between the foot jumping and the rope whirling tasks. Also, the median value of hand-foot deviation time was greater in the ADHD group (3.34 ms) than in the control group (1.75 ms). In RJ-V, the control group was able to modify their pace and respond to the target speed in the post-phase, while the ADHD group could not. Conclusion: Impaired timing perception leads to less accurate performance during rope jumping for ADHD children. The findings also reveal that poor hand-foot coordination results in poor control of simultaneous movements of the upper and lower limbs during rope jumping. Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Attention-deficit/hyperactivity disorder (ADHD) Timing Rope jumping

1. Introduction Time perception is the ability to estimate periods of time of coming events. Processing of timing in shorter intervals is based on skilled movements and cerebellar mechanisms without cognitive control, whereas, in longer intervals, it is associated with attention and working memory (Lewis & Miall, 2003a,b; Rammsayer, 1999). Previous studies have indicated that processing of precise timing tasks and longer timing intervals are associated with the cerebellum and basal ganglia (Ivry & Keele, 1989; Ivry & Spencer, 2004; Mangels, Ivry, & Shimizu, 1998). The network of right hemispheric frontocerebellar time discrimination has also been shown to be involved in timing tasks (Harrington, Haaland, & Knight, 1998; Smith, Taylor, Lidzba, & Rubia, 2003). The output of motor timing consists of two components: a clock component, which reflects time keeper intervals, and a motor delay component, which reflects motor implementation delay * Corresponding author. Tel.: þ886 7 3121101x2646; fax: þ886 7 3138359. E-mail address: [email protected] (W.-L. Wu).

(Harrington, Haaland, & Hermanowicz, 1998). Previous studies have indicated that children with ADHD have perceptual deficits in the clock component, such as in time production and reproduction, which further influences their performance on motor timing tasks (Barkley, Murphy, & Bush, 2001; Van Meel, Oosterlaan, Heslenfeld, & Sergeant, 2005; Yang et al., 2007). When rope jumping, it is necessary to coordinate the upper and lower body to maintain balance and rhythm. Rope jumping can enhance the precise coordination of multiple muscle groups, which is why it is used widely in athletic training programs (Lee, 2010). Rope jumping combines the angular momentum of the rope and vertical displacement of the body (Pitreli & O’Shea, 1986). Also, rope jumping involves upper and lower synchrony (hand-foot coordination) where positioning and timing is critical (Pitreli & O’Shea, 1986). The ability of time reproduction makes it possible to reproduce specified time periods with great precision (Toplak, Dockstader, & Tannock, 2006). Rope jumping skill involves good perception of time reproduction. However, poor motor timing performance has been found in children with ADHD. It seems that timing abnormalities have been related to impulsiveness, a core

1466-853X/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ptsp.2012.03.012

Please cite this article in press as: Chen, Y.-Y., et al., Timing perception and motor coordination on rope jumping in children with attention deficit hyperactivity disorder, Physical Therapy in Sport (2012), doi:10.1016/j.ptsp.2012.03.012

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Y.-Y. Chen et al. / Physical Therapy in Sport xxx (2012) 1e5

clinical symptom of ADHD (Rubia, 2002; Rubia, Halari, Christakou, & Taylor, 2009). It has been found that children with ADHD show less activity in regions including the prefrontal and precentral gyri, basal ganglia, cerebellum, inferior parietal lobule, superior temporal gyri, and insula, which are associated with sensorimotor timing (Valera et al., 2010). Thus, they have demonstrated deficits in time perception including shorter reproductions and greater reproduction errors than healthy children (Barkley et al., 2001). ADHD children have been shown to be impaired at maintaining a chosen tapping rhythm synchronously and in responding to organize their motor output (Rubia, Taylor, Taylor, & Sergeant, 1999). Children with ADHD showed poor ability to plan events which are separated by time (Barkley, 1997). Also, children with ADHD have problems executing motor output (Pennington & Ozonoff, 1996) and they exhibit slow output on automatic processing tasks (Carte, Nigg, & Hinshaw, 1996). It has been suggested that children with ADHD have difficulty adjusting their speed to motor tasks with external cues (Carte et al., 1996). Much evidence exists to suggest that children with ADHD have impairments in fine motor timing when executing finger tapping tasks. However, few studies have focussed on gross motor timing. Through clinical observation, it was found that children with ADHD showed poor performance when rope jumping. It has been suggested that problems with timing perception and motor coordination might be the reason. Thus, in this study, a series of rope jumping tasks involving different rope jumping rates was designed to evaluate the timing perception ability and motor coordination of ADHD children. 2. Methods 2.1. Subjects Five boys and five girls, with a mean age of 9.65
1.27 years, diagnosed as ADHD by a local hospital and without other combined syndromes, were recruited in this study. Ten age-matched nonADHD children (4 boys, mean age 9.93
1.54 years), without ADHD symptoms or other neuromuscular symptoms, were recruited from local schools as the control group. Rope jumping was already a part of the physical education curriculum at the time of data collection. Informed consent, approved by the university ethical review committee, was obtained from parents prior to involvement in the study. 2.2. Material A force plate (Kistler Instrument Corp, Winterhur, Switzerland) with the sample rate of 1000 Hz was used to record the flight timing of rope jumping. A six-camera motion capture system (Qualisys Motion capture Systems, Qualisys AB, Sweden), with a sample rate of 100 Hz, was used to capture rope movement using a reflective label attached to the distal end of the rope. Furthermore, the rhythm, as controlled by a metronome, was recorded by a CD player for use as our target signal before the test. 2.3. Procedure A reflective label was stuck to the distal end and on the middle of the rope in order to record the trajectory of the rope. Two reflective markers were stuck on each side of the third metatarsal head to help judge the flight phase and landing phase during rope jumping. Subsequently, participants were asked to warm up by doing rope jumping for at least 15 s before the formal rope jumping test; they then practiced three cycles at each tempo; 80, 100 and 120. The sounds at the various tempi were played during the task

by CD player. Each participant was allowed to take a rest during this study. Muscle fatigue was not an issue. Firstly, subjects were required to jump the rope at a constant tempo of 100 for 15 s (RJ-C). After 10 min rest, they were asked to jump at variable speeds, consisting of the tempos of 80e100, 80e120, 100e80, 100e120, 120e80, and 120e100, for 15 s (RJ-V), respectively, in a random order. Each participant was allowed to take a 3 min rest between these 6 trials. Under RJ-V, the tempo was changed at around the 6the7th second during each trial. The tempo of sound for each trial had been recorded before the experiment and was played continuously by CD player. Participants were instructed to do their best to follow the tempo and were required to jump inside the edges of the force platform. Each subject was instructed to finish 2 trials on RJ-C and only 1 trial on each RJ-V task to achieve a total of three acceleration trials and three deceleration trials. If a subject tripped on the rope and failed on the task, then they were asked to do more trials. The number of failures was recorded. 2.4. Data analysis The recurrent period of jumping (foot jumping cycle) was defined as the time span from when the ground reaction force first exceeded 10 N until the next time the ground reaction force exceeded 10 N, and so on. Similarly, the period of the rope cycle (rope whirling cycle) was defined by the rope marker reaching the lowest point and contacting ground. The “timing variation in jumping” and “timing variation in whirling” were calculated as the absolute value of the difference between 60 and the foot jumping cycle or rope whirling cycle, respectively; multiplied by the reciprocal of the tempo. The timing variation is the inconsistency between the manipulation of time by the performer and the expected manipulation of time for the task, the symptom of which is either an extended performance time or a shortened one compared with the expected time. Moreover, we subtracted the timing variation in whirling from the timing variation in jumping and found the absolute value to define the “hand-foot deviation time”. In the RJ-C task, two trials were analyzed. Each trial of the RJ-C task was analyzed from 4 to 9 s. In the RJ-V task, 6 different tasks were analyzed. Moreover, each trial of the RJ-V tasks was separated into three phases, which were selected as pre-phase (4e5 s), midphase (6e7 s), and post-phase (8e9 s). Finally, the mean values for hand-foot deviation time, timing variation in foot jumping, and timing variation in rope whirling from all the available rope jumping cycles of the RJ-C and RJ-V tasks were recorded. 2.5. Statistical analysis A non-parametric test (Mann Whitney U test) was used to assess the time difference between the ADHD group and the control group for RJ-C and RJ-V from 4 to 9 s. Also, a Mann Whitney U test was used to assess the difference between successful trials and failed trials for RJ-C. The statistical significance for paired comparisons between each phase was calculated using Wilcoxon Signed-Rank test method. All analyses were performed using SPSS 17.0 software (SPSS Inc., USA). Results were considered statistically significant when the p-value was less than 0.05. 3. Results Fig. 1(a) displays the median value of hand-foot deviation time from 4 to 9 s across the groups for the RJ-C task. The median value of hand-foot deviation time was greater in the ADHD group (3.34 ms), compared to the control group (1.75 ms) (p