Journal of Sports Science 3 (2015) 203-213 D doi: 10.17265/2332-7839/2015.05.001 DAVID PUBLISHING Aging Effects on Neuromuscular Activity in Karate Practitioners António Manuel Vitória Vences de Brito1,2,3, Mário André Ferreira Rodrigues1,2, Wojciech Jan Cynarski3,4, Carlos Gutiérrez García3,5 1. Sport Sciences School of Rio Maior, Polytechnic Institute of Santarém, 2040-413 Rio Maior, Portugal 2. Life Quality Research Centre-CIEQV, Complexo Andaluz, Apartado 279, 2001-904 Santarém, Portugal 3. International Martial Arts and Combat Sports Scientific Society—IMACSSS, 35-959 Rzeszow, A. Towarnickiego Str. 3/17A, Poland 4. Faculty of Physical Education, University of Rzeszów, Rzeszow 35-959, Poland 5. Department of Physical and Sport Education, Faculty of Physical and Sport Sciences, University of León, Vegazana Campus, 24071–León, Spain Abstract: Aging leads to a general decline in body functions that affects quality of life. Sports practice is recommended as a means to attenuate the impact of the aging process. The aim of this study was to identify and analyze the neuromuscular activity and its patterns on active karate practitioners and assess the effects of the aging process. Two groups of black belt male karate practitioners, one with nine practitioners over 50 years old and the other with 21 practitioners aged between 20-30 years old performed the frontal kick mae-geri. Kinematic and electromyographic data of five muscles were collected from the right leg. Results showed two distinct periods of muscular activation in the mae-geri performance, with similar muscles activity patterns between groups. Nevertheless, some differences were found in the muscles’ activity onset and offset, in root mean square and in inter-muscle delay and co-contraction periods. Those differences indicated that aging affects the neuromuscular activity in the mae-geri performance of the oldest karate practitioners. Nevertheless, the results showed that lifelong practice of karate can preserve the quality of the neuromuscular activity in older practitioners when they perform a kick, and this could be associated with benefits to balance control. Key words: Aging, motor control, neuromuscular activity, karate, combat sports, martial arts. 1. Introduction reduction of strength also depends on the decrease in mitochondria and mitochondrial DNA [7], with a After the third decade of life, humans start to reduction of synthesis of muscle proteins [8]. experience an aging-related decline in biological The neurological activity declines with aging, too functions that affect the locomotors’ performance [1], [9, 10]. At this level, changes occur in the detection of compromising their ability to do normal activities and visual, vestibular and somatosensory stimuli [11-13], to maintain the practice of sport. Those declines in processing the information [14] and in the response happen at the level of muscular strength production [2, through muscle contraction [15]. These changes are 3], with a decrease of maximal strength associated related to the loss of neurons and a decrease in the with loss of muscle mass, and atrophy, with a decrease functional capacity of the remaining neurons, leading in cross-sectional area of muscle fibers and a decrease to a decrease in the velocity of conduction in the nerve in the number of muscle fibers [4-6]. Age-related [16-19]. Proprioceptive receptors related with the control and determination of the limbs’ position and Corresponding author: António Manuel Vitória Vences de Brito, Ph.D., professor, research fields: kinesiology, movements continue to deteriorate with age, leading neuromuscular control and coordination, physiology and to a decrease in neuromuscular control and increasing injuries in sport. E-mail: [email protected]. 204 Aging Effects on Neuromuscular Activity in Karate Practitioners the risk of falls in the elderly [9, 20]. Tai Chi practice improves neuromuscular control, In association with neuromuscular control and which improves the balance and reduces the risk of strength production, other factors, such as longer falls. Similar conclusions about balance control were co-activation and co-contraction [21], or the reduction found in the Korean martial art Taekwondo [36], and of specific tension in muscles may contribute to the also improvements in muscular strength and flexibility age-related loss of force [22]. The co-activation and were noted [37]. co-contraction between agonist and antagonist In karate, the performance of specific skills is muscles are higher in the earlier ages, decreasing dependent on a high level of control and coordination progressively with maturation, and learning and of the limbs movements and balance, which is practice of skills [23]. There is a stabilization period dependent on effective neuromuscular control. [24], but the co-activation and co-contraction Consequently, aging can bring some problems to increases with aging, fundamentally after the fifth karate practitioners during the performance of their decade of life [25-27]. skills. Neuromuscular control patterns of the movements The latest research in karate has mainly focused on and the changes related with aging lead to changes in the kinesiological aspects of skills performance in the performance of both simple and complex skills. both regular and elite practitioners aged below 50 Several studies concluded that the changes in years old. Some researchers analyzed the movement time increase with aging [10, 14, 28, 29], neuromuscular patterns, kinematic and kinetic activity but the older people can perform motor skill activities of the punches [38-40], and others the kicks [41-45]. using similar control strategies to young adults [28]. However, research about the relationship between Rand and Stelmach [14] showed that several aging and karate practice has to be done. Thus, movement components were differently affected by considering the karate with a practice possible for life, aging, and this affected in different ways the decrease we must know and understand how the aging process of the overall performance. Those authors suggest the affects it, particularly in terms of neuromuscular existence of an age-related deficit in processing of activity, and the potential benefits to the quality of life sensory information, reducing the capability to plan of its practitioners. and organize sequential actions. The purpose of this study was to identify and The decline in neuromuscular function related to compare the neuromuscular patterns of activity in age [30, 31] can be slowed or delayed with regular veteran and younger black belt karate practitioners physical activity [6]. Studies about training in older during the performance of the frontal kick mae-geri to people confirm improvements in muscle strength [3, verify the existence of differences related to aging. To 32, 33], muscle power [34], explosive strength, fulfill this aim, the activity of the muscles of the hip walking speed and in balance. Improvements in the flexion, knee extension and foot plantar flexion were maximum oxygen consumption [1], as in the compared between the younger and veteran groups mitochondria functions [7] were found, which is during the performance of the mae-geri kick. We important for the contractile activity of muscles. hypothesized that continuous and regular karate Martial arts allow practitioners to maintain a regular practice will reduce the effects of aging process on and continuous practice throughout life, and some neuromuscular activity in older karate practitioners, studies related these practices with benefits in the preventing and attenuating the decrease in aging process. Gatts and Woollacott [35] showed that neuromuscular activity. Aging Effects on Neuromuscular Activity in Karate Practitioners 205 Table 1 Physical characterization of VetK and YgK practitioners. Age Height Weight Leg length Body fat Weekly training hours Black belt level Years of (years) (cm) (kg) (cm) (%) (h) (Dan) practice VetK 54 ± 4 ª 176 ± 5 76 ± 9 91 ± 3 19 ± 2 ª 5 ± 1 5 ± 1 ª 35 ± 10 ª YgK 23 ± 5 172 ± 7 72 ± 14 89 ± 5 13 ± 7 7 ± 4 1 ± 1 13 ± 4 VetK = Veteran karate practitioners. YgK = Young karate practitioners. Values are means ± SD. a Specifies statistically significant differences between groups (α ≤ 0.05). Fig. 1 Illustration of the experimental setup showing a veteran karateka facing the bag at the starting position of zenkutsu-dachi, with the right leg in backward extension, and the left leg flexed on the thigh and bent at the knee, with both feet on the floor, and the mae-geri kick movement until the final position of the foot in contact with the target. 2. Methods the performance of the mae-geri kick were recorded simultaneously. The kick was performed into a 2.1 Participants vertical floor training bag. The target area was at a Thirty male black belt karate practitioners with height of 90 cm from the ground and at a distance of more than 10 years of continuous practice volunteered each participant’s lower limb length. Participants to participate in the study. Two groups were formed; started from the typical karate static stance of one with nine veteran karate practitioners aged more zenkutsu-dachi (Fig. 1). They kicked in response to a than 50 years old (VetK), and the other with 21 karate sound stimulus activated by a trigger linked and practitioners aged between 20 and 30 years old (YgK). synchronized between the SEMG and the video All participants were in perfect health and without recording device. Each participant performed three history of neuromuscular or cardiovascular disease. fast and strong repetitions of the mae-geri kick with All participants signed an informed consent document. impact of the metatarsals, koshi, on the bag. There was The demographics of the two groups are shown in a rest period of 30 seconds between repetitions. The Table 1. median value of the three trials was used for analysis. This study was conducted according to the Helsinki 2.3 Apparatus Declaration and was approved by the scientific committee of the Sport Sciences School of Rio Maior, After skin preparation, electrodes were placed on Polytechnic Institute of Santarém, Portugal.