Full length articleEffect of changing water depth on muscle activity and motion kinematics during sit-to-stand motion
Introduction
The sit-to-stand (STS) movement is a fundamental activity, often used to initiate upright locomotion in daily life. The deterioration of the ability to perform STS movement leads to impairment of functioning and mobility in activities of daily living (ADL) and increased mortality [1,2]. Many studies have investigated the kinetics and kinematics of the STS movement [[3], [4], [5]] and have provided information on treatments for improving or preventing deterioration of the ability to perform STS movement.
Among the functional and rehabilitative training programs described, one option is an exercise performed while in water (“aquatic exercise”) [6]. Immersed in water, the human body is influenced by the properties of water, especially by buoyancy and viscosity, during movement [[6], [7], [8]]. Therefore, aquatic exercise is sometimes used for frail elderly persons [9,10]. Aquatic ADL exercises such as walking, STS, and climbing in frail elderly individuals improved quality of life, ADLs, and other body functions [9,10]. Many studies have investigated kinetics and kinematics while walking during aquatic exercises [7,8,11]. However, only a few studies have assessed ADL activities such as STS in an aquatic environment, although these activities are often used in functional and rehabilitation aquatic exercise training [12,13].
Lower mean muscle activity has been reported in the lower extremity during STS in water than on a dry surface (land) and higher muscle activity in the trunk muscles in water than on land [12]. Furthermore, lower extremity and trunk segment motion kinematics with muscle activity during the STS movement results in lower mean muscle activity in all muscles when immersed in water compared to STS on land [14]. Kaneda [14] also reported similar or higher integral muscle activity in water compared to that on land, except for the rectus femoris (RF), possibly due to the prolonged time spent in water. Evaluation of motion kinematics revealed that the range of motion (ROM) at the knee joint was smaller in water than on land. Moreover, smaller or larger postural differences at the knee and hip joint and trunk segment between the water and dry conditions were detected at the beginning and end of STS. Cuesta-Vargas et al. [15] investigated the effects of different seat heights of chairs in the water and reported no significant effects on muscle activity. Thus, differences between water and land-based exercises in muscle activity and motion kinematics during the STS movement were mainly due to the effects of buoyancy.
Buoyancy is the upward directional force that acts on the human body immersed in water. As the body is gradually immersed, the weight of the body is progressively offloaded [6]. Previous studies that assessed the ground reaction force (GRF) with changing water depth during walking showed a diminishing GRF with increasing water depth [16,17]. Similarly, some kinematic parameters are altered by changes in water depth during walking [16,18]. Previous studies have also investigated the effect of water depth on functional exercises such as squatting, calf raises, and jumping, as well as reported a decrease in the GRF with increasing water depth [19]. However, there has been no investigation on the effect of water depth on STS. Because the performance of the STS movement in water is mainly influenced by buoyancy, the effects of changes in water depth on STS should be investigated. This information would provide quantitative information for functional and rehabilitative training protocols.
This study investigated muscle activity and motion kinematics during STS on land and while partially immersed in water, particularly focusing on effects due to dynamic changes in water depth. The hypothesis was that muscle activity, and motion kinematics approached those on land as water depth decreased.
Section snippets
Participants
This study recruited 11 healthy male participants, who appeared in a previous study [14] in which there were 12 participants. The data for the present study were collected at the same time as the previous study [14], but one participant had been excluded from the analysis in the prior study because of missing data. Written informed consent was obtained before conducting the study. The present study protocol was approved by the Human Ethics Committee of Chiba Institute of Technology (approval
Results
The mean ± standard deviation (SD) of age, height, weight, and the body mass index of the participants were 29.4 ± 9.1 years, 174.4 ± 5.3 cm, 67.5 ± 5.6 kg, and 22.2 ± 1.9 kg/m2, respectively. The participants had no orthopaedic diseases that could affect STS motion.
The duration, mEMG, and angle of each joint and the trunk inclination in the shallow condition and the difference between the shallow and other conditions are shown in Table 1. Significant differences were detected by one-way ANOVA
Discussion
The mEMG was higher in the shallow STS than in the deep in the GAS, RF, and ES but decreased in the shallow compared with the land STS only for the RF. Furthermore, the present study also confirmed a higher correlation in the time series pattern in the land-shallow than in the land-deep in the TA, RF, and ES. These results were likely due to the decrease in weight offload as the water depth decreases [6,16,19]. Buoyancy and water drag forces have an influence on the human body during exercise
Declaration of Competing Interest
The author declares not conflicts of interest.
Acknowledgments
The author deeply thanks Takayoshi Takahashi, Ph.D., from Nobby Tech. Ltd. and Satoru Adachi for their significant assistance in conducting the present research. The author would like to thank Editage (www.editage.jp) for English language editing and revision of this manuscript. This work was supported by JSPS KAKENHI [Grant Number 15K16521].
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2020, International Journal of Environmental Research and Public Health