Kinematic Analysis of Daily Activity of Touching Lateral Shoulder for Normal Subjects

Abstract

Analysis of motion is needed in order to gain a better understanding of upper-limb movements. Biomechanical studies involving measurements of movement analysis are very important so that upper-limb activities can be explained. The purpose of this study was to describe the temporal analysis for different age groups and investigate the relationship between kinematical analysis movements of upper-limb joints in the “touching contra lateral shoulder” activity with different age groups. The activity included hand lifting, resting and returning the hand to the initial position with twenty healthy subjects between 24 and 56 years old (n = 60). The Vicon motion analysis system, which consists of three infrared and high-speed cameras, was used to analyze several kinematical parameters such as movement times, peak velocities and joint angles of the shoulder, elbow and wrist. Descriptive kinematic variables were obtained, and phase definitions were determined. There were significant differences among all age groups for total movement times and angles of the shoulder, elbow and wrist joints. The quality of movement dropped after subjects reached an age of 50. Thus, the analysis that segmented this age group may provide relevant information that will help improve the understanding of the motor system with advancing age.

1. Introduction

The activity associated with daily living includes basic, primary tasks performed by each person from childhood through adulthood. These tasks include bathing, dressing, combing hair, reaching, grooming, feeding, drinking and toileting. However, for patients with upper-extremity failure such as stroke that affected part of the brain, spinal cord injury (tetraplegia) impacting the spinal cord injury involving C1–C7 (tetraplegia), or rotator cuff impingement known as shoulder arthroplasty, activities of daily living become a very difficult task. It was found that in the drinking from a glass activity, the movement time for stroke patients was slower in any other task phase, and for the whole task, the mean difference in movement times was 4.9 s [1]. In both groups of subjects with tetraplegia, the reaching phase did not only take longer than in healthy subjects; this phase was also the longest phase in the cycle [2]. Two of the ten participants were not capable of completing the reaching task [3], and the shoulder arthroplasty patient group did not finish the combing task [4].

Some activities associated with daily living that utilise upper-extremity movements have been researched in the literature [5,6,7,8,9]. Murphy et al. [1] researched stroke patients, Gronley et al. [10] studied daily living activities for C6 tetraplegia patients, Reyes-Guzmán et al. [2] studied spinal cord injury, Hall et al. [3] studied rotator cuff impingement, and Veeger et al. [4] studied post-shoulder-arthroplasty patients.

In certain circumstances, a clinical assessment and diagnosis require some information about kinematic analysis. Therefore, a temporal analysis is important, especially for studying the upper-extremity pattern for positive capability efficiency performance at different phases of movement. To avoid complexity in measurements, facilitating the measurement and interpretation also produces similar outcomes with a similar pattern for related daily living activities using temporal analysis. These details should be examined in healthy subjects before the assessment of disabled subjects. In addition, information about how healthy subjects perform activities of daily living and measurements of the maximum joint angles of the upper extremity is still vague.

Apart from kinematic studies, several studies using EMG signals have been performed [11,12,13,14]. The studies focused on movement of the upper limb of healthy subjects. These studies have taken into account the muscle strength of healthy subjects that is used for controlling the upper limb in people with severe arm disabilities.

Typically, normal/control subjects were randomly selected between the ages of 20 to 40 years in the study of kinematic activities of daily living with a focus on specific diseases [2,4,15], and there are also studies that selected an elderly group with subjects over 50 years old [1,3]. Meanwhile, researchers assessing healthy subjects involved young adults in the age range between 18 and 35 years old [6,7,9,16] and the rest of the subjects in an adult age range between 18 and 55 years old in their studies [5,8,17,18,19]. Thus, an investigation of healthy subject movement when performing daily living activities for movement patterns of various age groups should be studied. This paper, however, reflects the behaviour of normal subjects in various age groups and has potential in clinical applications.

Previously, some researchers explained the temporal analysis activities of grasping [20,21], combing hair, reaching to turn on a switch, reaching for the perineum, drinking from a cup [10], and drinking from a glass [1,17]. Based on previous studies, there are no reports that analysed touching on the contralateral shoulder. This activity will resemble normal movement during the task of touching the contralateral shoulder.

Therefore, the objectives of the present study are to describe a temporal analysis for different age groups and to investigate the relationship between the kinematical analysis of movements of upper-limb joints in the touching-the-contralateral-shoulder activity for different age groups. In this study, two hypotheses were formed: (1) There are no differences in the means of the phases during performance of the activities, and (2) there are no differences in the means of total movement times, joint angles (shoulder, elbow and wrist) or elbow joint peak velocity among age groups in terms of kinematics analysis.

2. Methods

2.1. Participants and Study Design

The participants consisted of 20 control subjects (5 males and 15 females) with a mean age of 39.1 years (SD ± 10.3) in a range of 24–56 years old. The subjects were healthy and free from any injuries. The healthy condition was defined as a subject who does not experience any pain for the upper-limb segments during touching of the contralateral shoulder. Subjects voluntarily participated in this study. The criteria that excluded subjects were disability in muscles or neurological conditions that could affect arm function. The study was approved by the Research Ethics committee. All subjects received written information about this study, and written consent was obtained before the experiment was performed.

The heights of subjects were taken before the experiment was carried out. Measurements of the upper-extremity (upper arm, forearm and hand) segments were taken using a flexible measuring tape [17]. Measurements of the arm were taken while the subject stood upright, adducted the arm and flexed the elbow at 90°. Then, we defined a distance between the acromion and styloid process of the ulna.

The mean subject height was 160.7 cm (SD ± 10.2), and the range was 148–185 cm. The subject mean weight was 72.9 kg (SD ± 16.5), and the range was 51.5–102.0 kg. The mean right arm length was 57.9 cm (SD ± 4.8), and the range was 52–69 cm.

Table 1. Characteristics and demography of the sample analysed (n = 20).

Age Groups	20–29		30–39		40–49		50–59
	Male	Female	Male	Female	Male	Female	Male	Female
(n)	3	2	0	5	1	4	1	4
Height (m)
$\overline{x}$	1.67		1.64		1.57		1.55
SD	(0.07)		(0.02)		(0.04)		(0.03)
Weight (kg)
$\overline{x}$	75.2		76.7		60.2		79.4
SD	(9.66)		(8.0)		(4.6)		(4.8)
Length of the right arm (cm)
$\overline{x}$	59.2		60.7		56.9		54.6
SD	(3.0)		(2.0)		(1.7)		(0.9)

illustrates the detailed demography for each age group of healthy subjects. The important inclusive criterion for subjects was that they must use their dominant hand to touch the opposite side of their body.

2.2. Measurement Device

Shoulder movements were recorded using a Vicon motion analysis system (Oxford Metrics Ltd., Oxford, UK) with a recording rate of 100 Hz. The system used three infrared cameras to detect 14 reflective markers placed on the bony landmark of the upper limb of the subjects (Che-Nan and Rambely, 2017). Six spherical 9 mm and eight spherical 14 mm reflective markers were attached to the skin using double-sided tape. It was necessary to make sure the markers were placed on the superficial bony prominences to reduce the impact of skin movement [17]. In previous kinematic studies, the same position of markers was used [22,23,24].

2.3. Set-Up and Procedure

From the pilot study, movement did not disrupt or interfere with the natural physical movement of the bodies during lifting, resting and returning the arm to its original position. Subjects were instructed to perform each activity at least five times in a row at a comfortable speed. The subject was required to sit with their body resting on the head of the chair without movement throughout the experiment. The markers were placed on the knee, pelvis and shoulder joints for the purpose of having an anatomical seating position. The aim of the experiment was to observe the movement of the arms respective to the trunk.

The movement started with the subjects seated in the original position. The task began with the lifting of the hand and touching the contralateral shoulder. Then, the subject’s hand was required to rest temporarily before returning to its original position. This activity may represent other activities that affect the contralateral shoulder such as showering (washing the body) or wearing a jacket.

Each activity was carried out at least five times. Five trials were analysed, and the second, third and fourth trials were selected for further processing. This was done to ensure consistency in the analysis process so that the subject was familiar with each activity and with the environment in the laboratory. This was also necessary to ensure that the movement of the subject was performed in a natural progression and represented daily movement. Tasks were selected after extensive consultation with clinical staff and based on previous studies.

All of the subjects touched their contralateral shoulder using their dominant hand. Subjects were instructed to sit on a 45 cm high banquet chair. The setup is shown in Figure 1. Before the experiment started, subjects were asked to sit in the original position on a chair with their feet on the floor. The sitting original position was defined as an arm placed with the palm on the ipsilateral thigh. Subjects were asked manoeuvre their dominant hand and elbow so that the forearm segment was parallel with the ground.

The movement for touching the contralateral shoulder included moving the hand from the original position, lifting the hand to touch the contralateral shoulder, resting the hand on the shoulder for a while and returning the hand to the starting position. The subject was instructed to sit throughout the experimental movement. The aim was to ensure that activities occurred as normally as possible and to allow the subject to touch the contralateral shoulder without any major movements.

To obtain a comfortable position, subjects were allowed to try touching the contralateral side several times. When the subject was ready, the instructor announced “you can start now”, and the subject started touching his or her contralateral shoulder at a comfortable speed. Each subject performed at least five attempts each session depending on how well the computer automatically detected the marker.

2.4. Data Analysis

After the recording process was completed, each marker was identified by a technician using Nexus software, and data were captured using Vicon, which aims to ensure that each marker could be detected properly during the data capture process. In some recordings, markers were sometimes hidden or overlapped with other markers and could be detected automatically. In each analysis, a minimum of three recordings of 90% success were used for analysis of every subject. From three successful recordings, the mean was calculated as a measurement for each subject. For this activity, data movement was divided into three phases (lifting, resting and returning) based on movement data and timing for the activity. The definition of each phase is described in detail in the next section.

Our goal was to gather as much potentially useful information and data as possible to determine and define the parameters that proved clinically useful for the task of touching the contralateral shoulder using a camera system for various different patient age groups for the next study. After the graphical plots for the kinematic data recordings were analysed, the following variables were obtained for analysis in more detail:

• Time movement. The total movement time (total duration of the entire movement) was based on the definition phase for each predetermined phase.
• Joint angle. The aim of this study was to calculate the angle of each joint. Joint angles were obtained from digitised data. The shoulder angle was determined using a marker on the hips, shoulder and elbow joints. An elbow angle was ascertained by markers on the shoulder, elbow, and wrist joints. The angle of the wrist involved markers on the elbow, wrist and index finger. Examination of the experimental data for joint angle in the frontal planes was performed.
• Peak velocity. The velocities during the lifting phase (from three phases, namely lifting, resting and returning). It is known as tangential velocity (when a body is moving in a circular path, this velocity is measured at any tangent point). The angular velocity and the radius of the segment are closely related to tangential velocity. The angular velocity of the upper-limb joint ($\dot{{\theta }_s}$) during performance of touching ccontralateral shoulder was multiplied by the length of upper-arm segment ($l_{ua}$) to obtain a tangential velocity (${\dot{\theta }}_t$).
• Time to reach peak velocity and percentage of time with peak velocity. These values were calculated only for the lifting phases.
• Interjoint coordination. This coordination was calculated using the correlation coefficient (Pearson product moment correlation) during the movement of the shoulder and elbow joints for lifting and returning phases.

2.5. Statistical Analysis

Statistical analysis was performed using SPSS (V22). Mean and standard deviation for descriptive statistics were calculated for each age group. In statistical calculations, the mean of three successful recordings was used. The data were analysed and found to have homogeneity and be normally distributed. The mean difference of movement times, peak velocity and joint angles (angle of the shoulder, elbow and wrist) for different age groups were determined using a one-way analysis of variance (ANOVA). Since the number of samples was greater than the number of groups, the ANOVA test was valid for testing significant differences among groups.

3. Results

3.1. Phase Definitions

Three phases were categorised for touching the contralateral shoulder. The activity began by lifting the hand from the arm placed with the palm on the ipsilateral thigh, a stage known as phase 1. Then, the hand moved towards the contralateral shoulder. During this activity, the angle of the shoulder joint during horizontal adduction was expected to increase, and the angle of the elbow joint during flexion was expected to decrease. Next, the hand was placed on the shoulder for a few seconds in a stage known as phase 2, the resting phase. The angle of the shoulder was in cross-body adduction, while the angle of elbow joint was in the flexion position. Finally, the hand returned back to its initial position, and this was defined as phase 3, the returning phase. The angle of the shoulder joint during the abduction movement was expected to return to its original position, and the angle of the elbow joint during extension was expected to increase. The angles for shoulder, elbow and wrist joints during the touching-the-contralateral-shoulder activity are presented in Figure 2.

3.2. Movement Times for Whole Groups

Table 2. Kinematic variables for all subjects.

Kinematic Variable	Mean	SD	95% Confidence Interval
Movement times (s)
Lifting	0.8	0.2	0.7–0.9
Resting	0.6	0.3	0.4–0.7
Returning	0.7	0.2	0.7–0.8
Total movement times	2.1	0.5	1.9–2.3
Joint angle (°)
Shoulder
Lifting (horizontal adduction)	39	1.4	36–42
Resting (cross-body adduction)	47	1.9	43–51
Returning (abduction neutral)	32	1.2	30–35
Elbow
Lifting (minimum flexion)	70	1.9	66–74
Resting (flexion)	55	1.6	52–59
Returning (extension increase)	75	2.5	70–80
Wrist
Lifting	157	0.8	155–158
Resting	164	0.6	163–166
Returning	155	0.8	153–156
Peak velocity (PV) (m/s)
Elbow
PV for lifting	0.47	0.03	0.47–0.48
PV for returning	0.40	0.12	0.37–0.43
Time to PV in lifting (s)	0.27	0.08	0.11–0.48
Time to PV in lifting (%)	36.4	8.82	14.15–55.81
Joints Coordination
Pearson Correlation Coefficients
Lifting	0.985 **
Returning	0.989 **

** Correlation is significant at the 0.01 level (2-tailed).

shows the kinematic variables of normal subjects for the whole group, which were calculated based on the phase definition of mean movement times for each phase. Due to gravitational force, the mean movement time during the lifting phase was found to have the longest duration at 0.8 s compared to the resting and returning phases. The mean movement time during returning was 0.7 s, and when resting, the mean movement time was 0.6 s. During the resting phase, subjects were free to decide on their hand movements by placing their hand for few seconds at a comfortable rate. Therefore, the resting phase had the shortest duration with the highest standard deviation compared to the other phases, at 0.4–0.7 s with a 95% confidence interval. The total movement time for the whole group was 2.1 s for performing the whole activity. A study by Murphy et al. [17] found that normal subjects took 6.84 s to perform a drinking-from-a-glass daily activity.

3.3. Joint Angle for Whole Groups

The graph of joint angles versus time is shown in Figure 2. The kinematic data of joint angles for all subjects are displayed in Table 2. The mean angle for the shoulder joint during the resting phase was found to have the largest value at 47° compared to the lifting and returning phases at 39° and 32°, respectively. This result was due to the maximal performance of shoulder cross-body adduction during the resting phase. The mean angle for the elbow joint during the returning phase was found to have the largest value at 75° compared to the lifting and resting phases at 70° and 55°, respectively. This finding can be explained by the elbow when it returned to its original position, as the extension of the elbow joint increased. A study by van Andel et al. [9] found that during lifting, normal subjects took 60° ± 9° for elbow angle when performing the touching-the-contralateral activity. The wrist joint was found to have the highest angle value during the resting phase with a value of 164°. However, it was concluded that there was no major difference in wrist angle joints in any of the phases. The difference between maximum and minimum angles for shoulder and elbow joints was 24° and 49°, respectively. The difference in angles of elbow joints was greater than that of shoulder joints, because the elbow was extended in the starting position where the arm was placed on the ipsilateral thigh, whereas the shoulder joint was displaced only slightly during the initial position.

3.4. Elbow Joint Peak Velocity for Whole Groups

A graph of tangential velocity is shown in Figure 3. During the lifting phase, the touching-the-contralateral-shoulder movement produced only one peak. The peak value for the whole group was 0.47 m/s or the equivalent to 1.7 km/h. During a maximum of tangential velocity, the peak velocity of the elbow joint was obtained. The velocity profile was bell-shaped and smooth with a major characteristic peak. For each phase of lifting and returning, there were two peaks observed during the entire movement. The velocity profiles of both the lifting and returning phases were found to be similar.

3.5. Movement Times for Different Age Groups

Table 3. Kinematic variables for normal subjects by age groups.

Kinematic Variable/Age (SD)	20–29	30–39	40–49	50–59
Movement times (s)
Lifting	0.8 (0.1)	0.8 (0.1)	0.6 (0.1)	0.9 (0.1)
Resting	0.5 (0.1)	0.5 (0.1)	0.5 (0.1)	0.7 (0.2)
Returning	0.8 (0.1)	0.7 (0.1)	0.7 (0.1)	0.8 (0.0)
Total movement times	2.1 (0.3)	2.0 (0.2)	1.8 (0.2)	2.4 (0.2)
Joint angle (°)
Shoulder
Lifting (horizontal adduction)	39 (1.9)	36 (2.5)	37 (1.3)	45 (3.3)
Resting (cross-body adduction)	49 (2.6)	44 (3.6)	40 (3.2)	53 (3.6)
Returning (abduction neutral)	34 (2.4)	30 (1.3)	29 (1.9)	36 (3.3)
Elbow
Lifting (minimum flexion)	69 (2.9)	64 (3.7)	70 (2.9)	79 (3.4)
Resting (flexion)	55 (1.4)	50 (4.7)	56 (2.5)	60 (2.6)
Returning (extension increase)	72 (3.8)	70 (4.7)	74 (5.6)	84 (4.3)
Wrist
Lifting	160 (1.7)	155 (1.4)	158 (0.6)	154 (2.2)
Resting	165 (0.9)	166 (0.9)	164 (1.5)	164 (1.5)
Returning	159 (2.0)	153 (1.2)	153 (0.8)	154 (1.3)
Peak velocity (PV) (m/s)
Elbow
PV for lifting	0.45 (0.04)	0.49 (0.09)	0.44 (0.10)	0.49 (0.05)
PV for returning	0.38 (0.08)	0.44 (0.19)	0.40 (0.14)	0.39 (0.06)
Time to PV in lifting (s)	0.25 (0.09)	0.25 (0.05)	0.23 (0.04)	0.31 (0.08)
Time to PV in lifting (%)	34.25 (7.75)	37.61 (10.0)	32.24 (7.46)	38.19 (8.87)
Joints Coordination
Pearson Correlation Coefficients
Lifting	0.998 **	0.985 **	0.997 **	0.944 *
Returning	0.997 **	0.967 **	0.986 **	0.950 *

** Correlation is significant at the 0.01 level (2-tailed). * Correlation is significant at the 0.05 level (2-tailed).

shows kinematic variables of normal subjects that were separated by age group. We found a mean movement time of 0.9 s during lifting for the 50s age group, which was the longest duration compared to other age groups. During the returning phase, the 20s and 50s age group subject showed a similar value of 0.8 s. During the resting phase, the 50s age group subjects had the longest resting period at 0.7 s compared to the other age groups. The total movement times for the whole phase showed that the 50s age group recorded the longest time to complete the task, 2.4 s. In each phase as well as for the entire task, subjects in the 50s age group showed an increase in movement times. The difference of total movement times among the different age groups was 0.6 s, F_3,56 = 4.619, p = 0.006 for the whole phase. An ANOVA test showed a significant difference among all age groups with F_3,56 = 4.619, p < 0.05. To see which age group was significantly different, a post hoc test was performed. The significant differences of mean total movement times were observed between the 20s and 40s age groups compared with the 50s age group have been shown.

3.6. Joint Angle for Different Groups

The graphs of joint angle versus time for different age groups are shown in Figure 4. Table 3 shows the kinematic data of joint angles for subjects among the different age groups. The graphs of the joint angles of the shoulder and elbow showed smooth movement and similar profile patterns for both the lifting and returning phases while subjects performed the touching-the-contralateral-shoulder-task. Subjects in the 50s age group showed the greatest maximal extension and flexion in each phase for elbow joints and the greatest maximal abduction and adduction in each phase for shoulder joints.

During the lifting phase, differences of joint angles for the shoulder and elbow among age groups were found to be 9.2° and 14.6°, F_3,56 = 10.065, p = 0.000 for the shoulder joint and F_3,56 = 3.483, p = 0.022 for the elbow joint. During the resting phase, differences of joint angles for shoulder and elbow among age groups were found to be 13° and 9.2°, F_3,56 = 10.061, p = 0.000 for the shoulder joint and F_3,56 = 4.631, p = 0.006 for the elbow joint. During the returning phase, differences of joint angles for the shoulder and elbow among age groups were found to be 6.7° and 13.9°, F_3,56 = 11.485, p = 0.000 for the shoulder joint and F_3,56 = 2.570, p = 0.064 for the elbow joint. Differences in angles among maximum and minimum values of shoulder and elbow joints during lifting were F_3,56 = 5.326, p = 0.003 and F_3,56 = 3.647, p = 0.018, respectively. ANOVA was carried out to compare the joint angles of the shoulder, elbow and wrist (dependent variable) in the different age groups (independent variable), which contained four age groups (20–29, 30–39, 40–49 and 50–59). An ANOVA test showed a significant difference among all age groups with p < 0.05 in all phases for the age group involving angles of the shoulder and elbow joints except during the returning phase for the elbow joint. A significant difference also occurred for the lifting and returning phases of the wrist joint. Post hoc tests showed that significant differences existed for the mean angle of the shoulder joint for the whole task between the 30s and 40s age groups compared to the 20s and 50s age groups. Meanwhile, significant differences between the mean angle existed for the elbow joint during lifting between the 30s age group and the 50s age group. Post hoc tests for wrist joint mean angles showed a significant difference between the 20s age group and the 50s age group during the lifting and returning phases. This was due to the wrist joint angle producing little difference in wrist joint movements during the resting phase. Thus, the movements of the hand and arm segments were treated as one segment.

Differences between the maximum and minimum for the shoulder and elbow joint angles were calculated as shown in

Table 4. Difference of maximum and minimum values of joint angles during lifting phase.

	20–29	30–39	40–49	50–59
Shoulder	26 (1.2)	20 (1.5)	19 (2.8)	30 (1.2)
Elbow	46 (3.9)	50 (1.7)	45 (2.2)	56 (0.3)

. For the differences between maximum and minimum values of the shoulder joint angle, a significant difference of the mean angle was found between the 30s and 40s age group compared with the 50s age group. Meanwhile, for the difference between maximum and minimum values of the elbow joint angle, a significant difference was shown for the mean angle between the 20s and 40s age groups compared with the 50s age group.

3.7. Elbow Joint Peak Velocity for Different Age Groups

Table 3 displays the kinematic data for peak velocity, time to peak velocity and percentage of peak velocity among different age groups during the lifting phase. The differences of peak values of 0.06 m/s (0.22 km/h), F_3,56 = 0.568, p = 0.639 for the lifting phase and F_3,56 = 0.645, p = 0.59 for the returning phase indicated peak velocities for all age groups were similar for both the lifting and returning phases. Meanwhile, time to lifting for subjects in the 50s age group was found to be the longest with a value of 0.31 s (38.2%) to reach peak velocity. There was no significant difference in peak velocities of the elbow joint among all age groups with F_3,56 = 0.568 in the lifting phase and F_3,56 = 0.645 in the returning phase. p > 0.05 was shown by an ANOVA test.

3.8. Interjoint Coordination between the Shoulder and Elbow

Interjoint coordination between shoulder and elbow joints during the lifting and returning phases for the whole group are shown in Table 2. The Pearson correlation coefficients of interjoint coordination for these joints during the lifting and returning phases were 0.985 and 0.989, respectively. The results show a correlation and significance of 0.01 between the shoulder and elbow joints. Table 3 shows the correlation coefficient for the lifting and returning phases of normal subjects that have been separated by age group. Subjects in the 50s age group had a correlation coefficient and significance level of 0.05 compared to the other groups, which were at the 0.01 level. Interjoint coordination for shoulder and elbow joints of 20s and 50s age groups are shown in Figure 5. The interjoint coordination graph for the 20s age group is representative of the 20s, 30s and 40s age groups since the statistical results found that the 20s, 30s and 40s age groups were significantly different compared to the 50s age group.

4. Discussion

This study discussed the relevant two-dimensional kinematic analysis of touching the contralateral shoulder for normal subjects. Kinematic data were expressed for movement times, velocity and angle of joints as well as the interjoint coordinate between the shoulder and elbow joints for healthy subjects in different age groups. Analysis of phases was also divided into three phases that included lifting a hand, resting and returning it to the original position.

Several studies have been conducted on the kinematic properties of patients who have upper-limb problems [5,7,8,25], but no details or analysis about activities such as touching the contralateral shoulder have been reported except in studies by Chen et al. [6] and van Andel et al. [9].

The task of touching the contralateral shoulder is a relatively complex one in terms of kinematics. The task consists of several movements including lifting the hand, resting the hand on the contralateral shoulder and returning the hand to the original position. Most studies focused on forward reaching [1,17,26]. Only Magermans et al. [5], Murray et al. [8] and van Andel et al. [9] studied the task of touching the contralateral shoulder as performed by normal subjects, and Gronley et al. [10] studied spinal cord injury patients performing contralateral-shoulder-touching movements. However, these studies only looked at the angle joints at the shoulder and elbow. There are no studies, to our knowledge, that discussed in detail the act of lifting the hand. Therefore, this temporal analysis of the task of touching the contralateral shoulder can be considered as unique. Furthermore, the activity of touching the contralateral shoulder is not fully vision-assisted. There is no ultimate agreement among researchers on which main kinematic parameters should be used to analyse upper-body motor performance. Kinematic analysis has been widely used in clinical fields as discriminative or evaluation measures, which shows the importance of legitimate specific kinematic parameter quantities for upper-limb movement. Analysis of the upper limb should include variables from the following factors: movement times, smoothness or velocity, as well as variables describing compensatory movement patterns or interjoint coordination [1].

The aim of this study was to analyse two-dimensional kinematic differences of healthy subjects among different age groups during the touching-the-contralateral-shoulder activity. Previous researchers treated all subjects in one group, for example, van Andel et al. [9] with a mean (SD) age of 28 ± 5.7 years, Murray et al. [8] with a mean (SD) age of 34.3 ± 11 years and Magermans et al. [5] with a mean (SD) age of 36.8 ± 11.8 years. The mean (SD) age group in this study was 39.1 ± 10.3 years. Chen et al. [6], Murray et al. [8] and van Andel et al. [9] studied the touching of the contralateral shoulder by healthy subjects without separating the age groups. Studies on the elderly in performing daily living activities found out that the elderly found it difficult to perform activities compared to the younger group [27,28,29]. The current study differentiated each age group and found that there were differences in kinematic variables during the contralateral shoulder touching such as movement times and joint angles. The main finding of this study was that there were significant differences in kinematic variables between the 50s age group and the other age groups during the performance of touching the contralateral shoulder. The significant differences observed were the movement times and joint angles. Peak velocity with different age group variables showed no significant difference among age groups.

Murphy et al. [1,17] obtained total movement times of 4.9 s and 6.84 s, respectively, in five phases while subjects were drinking from a glass; meanwhile, this work obtained a total movement time of 2.1 s for three phases of the touching-the-contralateral-shoulder activity. We used movement times to measure the smoothness and efficiency of movement. The use of movement times can also be found in research conducted by Murphy et al. [1,17], Trombly et al. [30] and Cirstea et al. [31], which involved healthy and stroke patients. In our research, movement units were measured in all three phases (lifting, resting and returning) as well as total movement times for touching the contralateral shoulder. Identifying the movement times might be useful in the planning of treatment programmes and for the evaluation of treatment effects. These data give indirect information about movement qualities such as smoothness and efficiency, and time testing in clinical practice should not be underestimated [1]. In the current research, when the subjects were separated into age groups, total movement times were found to be significantly different between the 20s and 40s age groups compared with the 50s age group. The 50s age group had longer performance times compared to the other groups for touching the contralateral shoulder. The increment movement times for the 50s age group indicated that the performance of the 50s age group was slower than the other age group, which caused variability in flexion/extension movements.

The concept of two-dimensional joint angles plays an important role in the medical field. Our focus was on the joints angle for different age groups to identify any potential differences among groups of people in their 20s, 30s, 40s and 50s since stroke patients are typically in the 50s age category. We found that there were significant differences among different age groups, except for the angles of the elbow during a returning phase and the wrist during the resting phase.

In the work carried out by van Andel et al. [9], they specified that the elbow joint was fully extended at a value 180°. The starting position for the touching-the-contralateral-shoulder activity for the elbow joint was 100°. Different elbow joint values for the starting position were found due to different positions of the arm in a study by van Andel et al. [9], who began the activity with sitting in an anatomical standing style, while our work began by placing the arm with the palm on the ipsilateral thigh.

Since no detailed studies were found on the touching-the-contralateral-shoulder activity, this work was carried out to compare the angles of the elbow joint during an activity of lifting a block to shoulder height [8]. Murray et al. [8] stated that the maximum angles of the elbow when lifting a block to shoulder height was 103°. Our studies obtained a maximum elbow angle with a value of 106° during the lifting phase. Thus, it could be seen that the range of the elbow angles was similar. The minimum elbow angle obtained by Murray et al. [8] was 16°, but this study obtained a value of 55°, which may be caused by different movements of the touching-the-contralateral-shoulder activity. The results show that during the lifting phase, the arm produced a positive acceleration before reaching its maximum velocity and deceleration in the resting phase (Figure 4). The shoulder angle adducted horizontally at its maximum value in this phase (Table 2). The arm accelerated in a negative direction during the returning phase and achieved its maximum velocity while the elbow was fully extended right before the arm returned to its original position.

The movement of the arm joints must be well coordinated to obtain a smooth and accurate reaching trajectory. In the study, reaching for the target movement in a touching-the-contralateral-shoulder task was independent of visionary assistance. Interjoint coordination for the elbow and shoulder joints during lifting and returning phases for the 50s age group declined. (Interjoint coordination for the elbow and shoulder joint excursions). Thus, a separate analysis of the 50s age group could help to identify different motor control strategies in such a group. Further investigation would help to better elucidate these differences, which would lead to a better comprehension of neuromotor pathologies. Levin [32] suggested that a measure of interjoint coordination was able to provide beneficial information about the subject’s motor function. These results indicate a movement of the arm joints, and a smooth and accurate hand trajectory was obtained. This study showed that interjoint coordination produced a smooth and efficient movement in all age groups (Figure 5). Nonetheless, the interjoint coordination efficiency of the 50s age group decreased compared to the other age groups.

5. Conclusions

Kinematic analysis is an important tool in clinical research. In this study, a group of healthy subjects with ages ranging from their 20s to 50s were involved in the movement of touching the contralateral shoulder. The subjects were separated and categorised according to their age groups. The results show that the performance of the 50s age group differed significantly in terms of movement times and joint angles as well as a lower association of interjoint coordination compared to that of the young groups in the touching-the-contralateral-shoulder activity. The quality of movement of the group dropped after subjects reached an age of 50. Thus, the analysis that segmented the age groups may provide relevant information that will help to improve the understanding of the changes in the motor system with advancing age.