The relation between preparatory stance and trunk rotation movements

ELSEVIER

Human Movement

Science 15 (1996) 899-908

The relation between preparatory stance and trunk rotation movements Yuji Yamamoto

*

Research Centre of Health, Physical Fitness, and Sports, Nagoya Uniuersity, Furo-cho, Chikusa-ku,

Nagoya,

464-01, Japan

Abstract The influence of preparatory stance on rotation movement reaction time of the trunk by bending of the knee and hip joint(s) was examined in 12 subjects. Four preparatory stances were examined: straight knee and hip extension (STAND), slight flexion of knee joints and hip joint (LIGHT), deep flexion (DEEP), and free initial position, i.e. that felt to be the most comfortable and effective (FRFE). There was no significant influence of the preparatory stance on hip latency, but there were significant differences between the preparatory stances on response time (RT) and movement time (MT). Furthermore, using a quadratic curve fitting technique, knee joint angles of 24.8 degrees and a hip joint angle of 23.3 degrees were shown to be the optimum flexion angles in the preparatory stance for the initiation of quick trunk rotation movements. It is proposed that mechanical factors have considerably more effects on trunk rotation movements than does the nervous system. PsyclNFO Keywords:

classification: Preparatory

2330

stance; Rotation;

Reaction time

1. Introduction A stance for moving quickly, forward, backward and laterally, is important in many sports skills, especially in ball games. Traditionally, it was believed that

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bending the knees, and having the weight over the balls of the feet, helps ensure the quickest response. Howorth (19461, from observing many body positions in everyday life, described basic dynamic stance positions in sport which involved bending at the elbow joints, at one hip joint, at the knee joints, ankle joints (slightly), and with the head bent forward, and trunk slightly bent. He described this stance as basic for movement accurateness, smoothness, strength, balance, good timing, rhythm, and coordination. However, in response to various directions and movements following the prepared stance, the best stance for quickest response has been questioned @later-Hammel, 1953; Cotten and Denning, 1970). MacKenzie (19921, from detailed analyses results of grasping movements, considered that human prehension can be viewed in terms of high level constraints, such as the goal of the action and knowledge based on past experiences; physical constraints in terms of object properties and environmental characteristics, and sensorimotor constraints relating to the performer’s anatomy and physiology. Marteniuk et al. (1987) made even more explicit the notions of task constraints on speed and accuracy. Taking a task-specific view of movement planning and control recognizes the importance of the interaction of the performer with the environment under given movement goals. Meinel (1960) observed sports skills from the viewpoint of morphology, and proposed that movement be considered as phase structure. He assumed that the preparatory phase had an important influence on the main phase in non-cyclic movements (e.g. tennis strokes). Physical movement, in this preparatory phase, involves rotation movements of the trunk - movements that are important in many sports skills. Such a viewpoint would predict that the preparatory stance is optimized and specific to the unique requirements that arise from rotation movements of the trunk in the preparation phase. With this in mind, this study was designed to examine the influence of bending of the knee joints and hip joint in the preparatory stance on reaction time of rotation movements of the trunk.

2. Method 2.1. Subjects Twelve male undergraduate students at Nagoya University served as paid subjects. Each subject was tested individually in single l-hour sessions.

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Human Movement Science 15 (1996) 899-908

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2.2. Apparatus

Subjects stood in an illuminated, sound-attenuated room throughout each session. Visual and auditory stimuli were presented by a MITSUBISHI HC39PEX colour monitor viewed at a distance of about 1 m. The responses with the right or left foot were made by depressing the microswitch embedded in the floor 20 cm behind the subject. Stimulus presentation, response collection and the triggering of other computer systems was controlled to the nearest millisecond by a digital computer (NEC98VX). Two goniometers (Penny and Giles) were taped to the subject’s leg and used to measure hip and knee joint angle changes in a sagittal plane. The signals from the goniometers were digitized to a resolution of 12 bits and sampled at 1 kHz by another computer (EPSON PC-286LS). To record trunk rotation movement, Light-Emitting Diodes (LEDs) were fitted to four points on a wooden rod attached to the subject’s waist. Movements of the LEDs were registered by means of an infrared camera coupled to a LED control unit (LCU) and a NOVA microcomputer (SELCOM SELSPOT II). The camera was positioned 2.5 m above the LEDs. The LCU was responsible for the timing of the signals of the LEDs and the conversion of the camera signal to digital position signals. The signals were sampled at 312.5 Hz. The root mean square error for the SELSPOT II data was less than 6.0 mm. Displacement records were digitally smoothed with a second order 14 Hz low-pass Butterworth filter. The initiation of the trunk rotation movement was set at 0.02 deg. SC’. A schematic diagram of the experimental set up is shown in Fig. 1. 2.3. Procedure The subject stood, in the prepared stance, on foot marks whose distance apart was equal to the width of the shoulders. The four upright initial positions that were required during each series were full knee and hip extension (STAND), slight flexion of knee and hip joint (LIGHT), deep flexion (DEEP), and the free initial position felt to be most comfortable and effective by the test subject (FREE). All subjects had 45 trials comprising 15 right, 15 left and 15 catch rotation trials at four prepared stances. The order of the prepared stance was varied for each subject. Each test series was recorded after the subjects had practised it under each condition. During the presentation of a warning signal of 2 s duration, the subject took one of the four predefined prepared stances. When the warning signal was turned off, a preparatory period of 0.75, 1, or 1.25 s duration started in a randomized order with an even probability. On the ‘go’

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SELSPOT

CAMERA

GONIOMETER (Penny & Giles

I

lm

20

inch colour MITSUBISHI

(NEC

PC9801VX)

Fig. 1. Schematic diagram of the rotation movement reaction time of trunk and recording

systems.

signal, the subject was required to rotate his trunk in the required direction and to depress the microswitch by foot as quickly as possible, or to stop the rotation movement when the target appeared at the centre of the monitor. Feedback information about reaction time, i.e., the duration between the ‘go’ signal and depression of the micro switch, was displayed immediately following a trial for 2 s on a monitor. The intervals between the series were about 5 min, and the subject was permitted to sit down to rest on a chair.

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2.4. Data processing The data were analyzed by using three measures computed on each trial. Hip latency (I-IL) was computed as the duration between the presentation of the ‘go’ signal and the initiation of trunk rotation movement; movement time (MT) was computed as the duration between the initiation of the trunk rotation movement and the time at which the micro switch was depressed by the foot; response time (RT) was defined as the duration between the presentation of the ‘go’ signal and the time at which the micro switch was depressed by the foot. Trials with RTs + 3 standard deviations from the subject’s mean were excluded from analysis. The flexion angles of the knee joint and hip joint in the preparatory stance were defined as the mean angles during the 2 s period before the presentation of the ‘go’ signal.

3. Results 3.1. Preparatory stance All subjects demonstrated small deviations in the knee joint and hip joint angles because there were not any specific directions or explicit restrictions on the preparatory stance of the subjects. Table 1 shows average mean angles with standard errors. The repeated measures analysis of variance on these data yielded significant main effects for preparatory stance conditions (knee joint angles; F(3,33) = 66.15, p < 0.001, hip joint angles; F(3,33) = 30.90, p < 0.001). Knee joint angles of the DEEP condition were significantly different (F(1,33) = 54.45, p < 0.001, F(1,33) = 53.28, p < 0.001, F(1,33) = 198.26, p < 0.001) in comparison with the DEEP and LIGHT, DEEP and FREE, and

Table 1 Means and standard errors of knee joint and hip joint angles (degrees) for each condition

across subjects

Condition

STAND

LIGHT

DEEP

FREE

Knee joint angle

0.70 (0.387) 0.92 (0.768)

16.23 (1.580) 10.87 (1.521)

34.86 (2.793) 34.10 (4.101)

16.43 (2.220) 19.87 (4.099)

Hip joint angle

Note: Averaged

values for all subjects are shown with standard errors in parentheses.

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DEEP and STAND conditions, respectively. The knee joints of the LIGHT and FREE conditions were significantly larger in flexion angle than those of the STAND condition (F(1,33) = 44.91, p < 0.001, F(1,33) = 45.99, p < 0.001) in comparison with the LIGHT and STAND, and FREE and STAND conditions, respectively. There was no significant difference between LIGHT and FREE conditions in knee joint angles. The hip joint angles of the DEEP condition were significantly deeper (F(1,33) = 41.99, p < 0.001, F(1,33) = 15.76, p < 0.001, F(1,33) = 85.69, p < 0.001) compared to the DEEP and LIGHT, DEEP and FREE, and DEEP and STAND conditions, respectively. In the FREE condition the hip joint showed significantly larger flexion than in the LIGHT and STAND condition (F(1,33) = 6.30, p < 0.05, F(1,33) = 27.96, p < 0.0011 in comparison with the FREE and LIGHT, and FREE and STAND conditions, respectively. There was a significant difference between the LIGHT and STAND condition in hip joint angles (F(1,33) = 7.71, p < 0.01). Although there was a significant difference between the LIGHT and FREE condition only for hip joint angles, it was considered that a different preparatory stance was taken in each different condition. 3.2. Trunk rotation reaction time Means of HL, MT and RT in each preparatory stance condition and the direction of trunk movement with standard errors are shown in Table 2. A repeated measures analysis of variance on HL yielded neither significant main effects for direction of trunk movement nor preparatory stance condition. It showed that rotation direction of trunk and preparation stance do not influence the time when a rotation of the trunk is initiated. There were significant main

Table 2 Means and standard errors of HL MT, and RT (ms) for each condition

across subjects

Condition

STAND

LIGHT

DEEP

FREE

HL

283.3 (10.13) 420.3 t 17.22) 703.60 (17.33)

281.5 (9.62) 379.7 ( 18.42) 661.2 (17.71)

291.0 (8.15) 378.8 (15.85) 669.70 (14.08)

288.2 (8.03) 341.6 f 17.60) 629.9 (16.60)

MT RT

Note; Averaged

values for all subjects are shown with standard errors in parentheses.

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effects only for preparatory stance on MT and RT (F(3,33) = 13.18, p < 0.001; F(3,33) = 20.37, p < 0.001, respectively). As a result of having compared the mean of each preparation stance condition, the FREE condition showed a significantly shorter MT and RT (MT; F(3,33) = 39.48, p < 0.001, F(3,33) = 9.28, p
HL

MT

RT

800

600

Experimental

condition

Fig. 2. Averaged across subject values are shown with standard errors for three dependent and RT, for each preparatory stance condition. * * p < 0.01. * * * p < 0.001.

variables;

HL, MT.

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Movement Science 15 119961899-908

STAND, and LIGHT and DEEP conditions, respectively); the STAND condition showed longer MT and RT than the LIGHT and DEEP condition (MT; F(3,33) = 10.48, p < 0.01, F(3,33) = 11.12, p < 0.01, RT; F(3,33) = 19.38, p < 0.001, F(3,33) = 12.61, p < 0.01, compared to the LIGHT and DEEP condition, respectively). There were no significant differences between LIGHT and DEEP conditions on either MT or RT. A mean and standard error for each preparatory posture condition is shown in Fig. 2. The results show that laterality was not observed in bilateral rotation movements, and shortening movement times of lower extremities were due to changing preparation stance, and that reaction time shortened as a result. 3.3. Optimum jlexion angle To obtain optimum flexion angle of knee joints and hip joints in the preparatory stance, quadratic curve fitting was applied to the data for each subject, using knee joint and hip joint angles as independent variables and RT as a dependent variable. The hypothesis of this analysis was that there is an optimum flexion angle for each dependent variable for each subject. In other words, a U-shaped curve will be applied to the relationship between flexion angle and RT. When a result of regression analysis was significant, the minimal value was computed and the value was defined as optimum flexion angle. As a result, significant regression is shown for knee joints in ten subjects with RT, and for hip joints in nine subjects with RT and each optimum flexion angle was calculated from 12 subjects. The average optimum flexion angle of the hip joint was 23.3 + 8.8 degrees and of the knee joint 24.8 + 6.1 degrees. In other words, when the preparation stance involves 25 degree angles at the hip and knee joints, the trunk rotation reaction time shortens the most. This optimum flexion angle may not accord with the flexion angles of a subject’s stance in the FREE condition which was considered for quickest response. Therefore, it is suggested that learning of the preparation stance leads to a shortening of the reaction time of bilateral rotation movements.

4. Discussion

This experiment examined the relationship between preparatory stance and reaction time of rotation movements of the trunk which is an important movement in sports skills. Although there was no significant influence of

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preparatory stance on HL, there were significant differences between preparatory stances as indexed by RT and MT measures. The relation between reaction time of subsequent movements and preparatory stance that deal with flexion of knee joint and centre of gravity position @later-Hammel, 1953; Cotten and Denning, 1970) and with an open and closed foot stance (Loockerman, 1973) were also studied. The mechanism, however, was unclear. Some studies have shown that preliminary muscular tension shortens reaction time - in particular premotor time. Schmidt and Stull (1970) re-examined Clarke’s experiment (Clarke, 19681, and studied premotor RT and motor RT in a situation in which a hand squeezed a gripping device to one of three submaximal tensions, and reacted to either an auditory or visual stimulus by squeezing as quickly and forcefully as possible. As a result, they found premotor RT shortened and motor RT lengthened with increased pre-tension. They interpretated this finding in terms of the ‘Memory Drum Theory’ of Henry and Rogers (1960). In other words, partial programming could account for the premotor RT changes by preliminary muscular tension. While this interpretation relates to efferent motor command, other studies have suggested that a shortening of reaction time is a consequence of afferent feedback. Furubayashi and Kasai (1990), for example, studied the influence of starting positions of the forearm on premotor reaction times and motor times for elbow flexion. They proposed that the MT difference was based on the change, not only in the number of synergic muscles participating, but also in the timing of synergistic muscles participating in an intended movement, and pointed to the influence that the proprioceptive and joint l&aesthetic afferent input has on decreases in motor time. The influence of preparatory stance only had an effect on RT and MT in the results of the present experiment. On HL, there was no clear effect. Because premotor time was not measured in this experiment, no mention can be made about the influence that afferent feedback might have on shortening of reaction time. Generally, the effect of preparatory stance would seem to be mediated by a removal of restrictions on hip external rotation by tension in the iliofemoral ligament due to flexion of the hip. The range of motion becomes large, and it is thought that this, in turn, results in a shortening of the mechanical movement time of the lower extremities. In other words, in large rotation movements of the trunk, it is thought that mechanical movement efficiency has a bigger influence on the reaction time than preparedness of the nervous system. In the present experiment, however, HL and RT were not measured by the same instrumentation. Additional factors might include change from front to back in the direction

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of the centre of foot pressure, shift of position of centre of gravity and flexion of ankle joint. These need to be analyzed using more precise instrumentation. In analyzing the pooled subject data, the laterality in the reaction time of the rotation direction of the trunk was not significant. When the data of individual subjects in the FREE condition was considered, one showed a significantly decreased rotation reaction time to the right, another a significantly decreased reaction time to the left in terms of HL. Three subjects showed significant decreases in rotation reaction time to the right. There is, thus, the possibility that differences in laterality relate to the direction of the rotation of the trunk. Consequently, there would appear to be the possibility to improve the weak side of rotation movements by learning and training. The issue of laterality is important in movements involved in many sports, as is the preparatory stance - flexion of knee and hip joints - for quick trunk rotational movements.

References Clarke, D.H., 1968. Effect of preliminary muscular tension on reaction latency. Research Quarterly 39, 60-66. Cotten, D.J. and D. Denning, 1970. Comparison of reaction movement times from four variations of the upright stance. Research Quarterly 41, 196-199. Furubayashi, T. and T. Kasai, 1990. Influence of initial forearm position on premotor times (PMTs) of the biceps brachii during an elbow flexion task. Human Movement Science 9, 583-598. Henry, F.M. and D. Rogers, 1960. Increased response latency for complicated movements and a ‘memory drum’ theory of neuromotor reaction. Research Quarterly 31, 448-458. Howorth, B., 1946. Dynamic posture. Journal of American Medical Association 131, 1398-1404. Loockerman, W.D., 1973. A comparison of the open and closed foot stance for reaction and movement times. Journal of Motor Behavior 5, 57-63. MacKenzie, C.B., 1992. ‘Constraints, phases and sensorimotor processing in prehension’. In: GE. Stelmach and J. Requin (Eds.), Tutorials in motor behavior II. Amsterdam: North-Holland. Marteniuk, R.G., CL. MacKenzie, M. Jeannerod, S. Athenes and C. Dugas, 1987. Constraints on human arm movement trajectories. Canadian Journal of Psychology 41, 365-378. Meinel, K., 1960. Bewegunslehre. Berlin: Volk und Wissen Volkseigener Verlag. pp. 149-154. Schmidt, R.A. and A. Stull, 1970. Premotor and motor reaction time as a function of preliminary muscular tension. Journal of Motor Behavior 2, 96 110. Slater-Hammel, A.T., 1953. Initial body position and total body reaction time. Research Quarterly 24, 9 I-96.