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Journal of Strength and Conditioning Research, 2006, 20(1), 145–150 q 2006 National Strength & Conditioning Association

THE EFFECT OF THE DIRECTION OF GAZE ON THE KINEMATICS OF THE SQUAT EXERCISE DAVID V. DONNELLY,1 WILLIAM P. BERG,2 AND DARRYN M. FISKE3

1Department of Intercollegiate Athletics, Miami University, Oxford, Ohio 45056; 2Department of Physical Education, Health and Sport Studies, Miami University, Oxford, Ohio 45056; 3Department of Athletics, St. Bonaventure University, St. Bonaventure, New York 14778.

ABSTRACT. Donnelly, D., W.P. Berg, and D. Fiske. The effect of the direction of gaze on the kinematics of the squat exercise. J. Strength Cond. Res. 20(1):145–150. 2006.—The purpose of this study was to determine whether the direction of gaze influences the kinematics of the squat exercise. Ten men experienced in the squat exercise performed a total of 30 repetitions of the squat in the form of 2 sets of 5 repetitions under 3 different conditions. Conditions varied with respect to the direction of the subjects’ gaze as they performed the exercise. Condition D en- tailed gazing downward at the intersection of the facing wall and the floor throughout the exercise. Condition S required subjects to gaze straight ahead at their own reflection (eyes) in the mirror on the wall directly in front of them. Condition U involved gaz- ing upward at the intersection of the facing wall and the ceiling throughout the exercise. Dependent variables included the lin- ear displacement of the bar and hip, linear velocity of the bar, and the angular displacement/position and velocity of the head, trunk, hip, and knee. The mean data were subjected to a re- peated measures analysis of variance, and, where appropriate, pairwise comparisons using Tukey’s Studentized Range Test. The results revealed overall similarity in movement kinematics when performing the squat exercise using the 3 different gaze directions. In particular, the upward and straight gaze condi- tions were not differentiated by the analysis. Conversely, the downward gaze was shown to increase the extent of hip flexion (F[2, 9] 5 4.82, p , .05), especially relative to the upward gaze, and possibly trunk flexion as well (F[2, 9] 5 3.02, p 5 .07). In terms of the practical application, because excessive hip and trunk flexion in the squat are contraindicated, cautioning ath- letes against allowing the head or direction of gaze to drop below a neutral position appears to be warranted.

KEY WORDS. weight training, vision, stability

INTRODUCTION

T he squat exercise involves most major muscle groups of the trunk and legs, and is one of the most beneficial muscle strengthening exercises. The squat not only enhances performance in

many sports, but has become an important component of general-purpose weight training programs as well. Be- cause of the number of muscle groups involved, squats also can positively stimulate the cardiovascular system (8, 9, 10). Moreover, when performed correctly, the squat can help prevent injuries (2, 6).

To obtain the desired training effects and to ensure safety, proper technique should be used when performing the squat. There is general agreement about what con- stitutes appropriate squat technique, with at least 1 ex- ception. There is some lack of clarity about how the head should be positioned during the squat, or more precisely, where a performer’s gaze should be directed—upward, downward, or straight ahead? According to Fry, using an

incorrect head position can cause poor body alignment and predispose an athlete to injury (5). What is the cor- rect head position and/or direction of gaze in the squat?

According to Francoeur, lifters should focus on a spot on the wall or ceiling, as this will help to keep the head up throughout the entire motion (4). Global Health and Fitness also recommends looking upward throughout the exercise (7), whereas O’Shea simply recommends keeping the head up (16). Westcott (17) and other professionals instruct exercisers to keep the head neutral throughout the exercise. Indeed, Kelso et al. advise that the head should face straight forward throughout the exercise (12). Some recommendations are more specific, such as that the head and neck should be kept straight with the eyes looking straight ahead (3, 5, 11,).

Some professionals warn against allowing the head and eye focus to drop from a neutral position, arguing that this could result in excessive forward lean as the lifter descends (3). Forward lean is a nontechnical de- scriptor of what we will refer to as trunk flexion. Trunk flexion is the forward deviation of the trunk relative to the vertical and can result from hip and knee flexion, as well as ankle dorsiflexion. In short, a head-down position during the squat exercise may increase the likelihood of excessive trunk flexion. Several authors have suggested that excessive trunk flexion during the squat can cause undue stress to be applied to the lumbar spine, and thus increase the chance of injury (3, 5, 14, 15).

On the contrary, Hill warns against using a head-up, eyes-up technique, arguing that balance is compromised, increasingly so during descent, making lower back strain more likely (3). Instead, Hill argues that the head and eyes should be straight or slightly down throughout the exercise. The latter recommendation is the only one, to our knowledge, suggesting that a downwardly directed gaze or head position is acceptable. Nonetheless, in spite of the general bias among experts against looking down- ward during the squat, athletes and weight trainers sometimes can be observed doing so.

Adding to the uncertainty about appropriate head po- sition and direction of gaze during the squat exercise is the fact that head position and direction of gaze are not synonymous. Ignoring the movement of the body as a whole, humans can redirect gaze by (a) moving the head with the eyes fixed in the head, (b) moving the eyes with the head fixed, or (c) moving the eyes and the head si- multaneously. A recommendation such as O’Shea’s to keep the head up during the squat (16) does not ensure that gaze will be directed upward as well. Of course, head position and direction of gaze likely are related; concern-

146 DONNELLY, BERG, AND FISKE

ing recommendations for squat technique, however, it is a mistake to assume they are equivalent. What is it that matters: head position, direction of gaze, both, or neither?

Theoretically, the direction of gaze during the squat exercise is potentially important, because it could affect posture and stability. Vision can be critical for movement control during the squat, particularly regarding balance/ stability (1). Accurate perception of self-motion is funda- mental to maintaining stability, and the direction of gaze could influence a lifter’s perception of self-motion. For ex- ample, looking upward toward the ceiling during the squat exercise could decrease sensitivity to information about the position of one’s body relative to the proximal support surface (floor). Information about one’s position relative to the floor is salient because it is useful for de- termining when to terminate the descent portion of the exercise and to begin the ascent. Selecting the correct point to change direction is critical, because a failure to do so could result in a loss of balance, leading to injury of the knee or back, or even causing the athlete to fall.

In contrast, directing one’s gaze downward toward the floor during the squat could decrease sensitivity to infor- mation about the position of one’s body relative to a wall or objects directly in front of the lifter. Perceiving ap- proach to or withdrawal from objects and surfaces direct- ly in front of us allows us to perceive forward and back- ward sway, respectively, and is critical for maintaining an upright posture (13). By looking at the floor, a per- former might fail to perceive postural sway in time to retard the forward or backward rotation of the body, which could result in a fall.

What about head position during the squat exercise? Theoretically, head position is important because it could possibly affect posture and stability, though more straightforwardly so than direction of gaze influences sta- bility. For example, Fry contends that the head and neck can be considered continuations of the vertebral column (5), implying that head position has a direct effect on body alignment, irrespective of the direction of gaze. It is ob- vious that improper body alignment, such as allowing one’s center of gravity to escape the confines of the base of support, could be detrimental to performance or even dangerous.

Because of the lack of agreement concerning head po- sition and direction of gaze in the squat exercise, and giv- en its probable importance to stability and safety during the performance of that exercise, the purpose of this study was to determine whether direction of gaze influ- ences the kinematics of the squat. As previously ex- plained, when referring to the squat exercise, strength and conditioning professionals appear to consider head position and direction of gaze to be synonymous or nearly so, but they are not. We chose to manipulate the direction of gaze rather than head position, because the former is far more easily and precisely controlled. Naturally, anal- yses of the results included the extent to which direction of gaze and head position were associated.

We also chose to evaluate anterior/posterior displace- ment of the bar, as well as hip and linear velocity of the bar, as measures of postural sway, and thus, indicators of stability. We also chose to characterize the angular ki- nematics of the trunk, hip, and knee to determine if the direction of gaze affects the overall coordination dynamics of the squat. Because of the potential link between exces- sive trunk flexion, undue stress to the lumbar spine, and

injury risk (3, 6, 14, 15), we were particularly interested in evaluating trunk flexion across different gaze direc- tions. Our hypotheses were that a downward gaze would result in a greater trunk flexion, as well as greater pos- tural sway (instability), than either the straight or up- ward gaze conditions. We also anticipated that the up- ward and straight gaze directions would yield similar lin- ear and angular squat kinematics.

METHODS Experimental Approach to the Problem

A repeated-measures design was used to determine the effect of the direction of gaze (downward, straight ahead, or upward) on the kinematics of the squat exercise. De- pendent variables included the linear displacement of the bar and hip, linear velocity of the bar, and the angular displacement/position and velocity of the head, trunk, hip, and knee.

Subjects

The subjects for this study consisted of 10 young men (mean age 5 20; SD 5 1.3; range, 18–22 years) who were members of the Miami University football team. Each subject had at least 1 year of experience performing the squat exercise. The subjects ranged in height from 1.78– 1.96 m and ranged in weight from 84–136.2 kg. The in- vestigation was approved by the Miami University Insti- tutional Review Board for Human Subjects.

Procedures

The apparatus used to perform the squat exercise con- sisted of a power rack, a York Olympic 20.43-kg bar (York Barbell Co., York, PA), and Olympic-sized weight plates. The rack was positioned such that subjects faced a mir- rored wall (at a distance of 1.5 m.) while performing the exercise. Subjects performed a total of 30 repetitions of the squat exercise in the form of 2 sets of 5 repetitions under 3 different conditions. The conditions varied with respect to the direction of the subjects’ gaze as they per- formed the squat. Condition D entailed gazing downward at the intersection of the facing wall and the floor throughout the exercise. Condition S required subjects to gaze straight ahead at their own reflection (eyes) in the mirror on the wall directly in front of them. Condition U involved gazing upward at the intersection of the facing wall and the ceiling (height 5 2.79 m) throughout the exercise. The order in which the conditions were per- formed was counterbalanced across subjects. The inten- sity for each subject was set at 25% of his 1 repetition maximum (1RM) in the squat exercise. The purpose of choosing a relatively light load was to minimize the ex- tent to which fatigue would influence squat kinematics. Normally, one could expect counterbalancing the order in which conditions are presented to completely control for any order effect resulting from fatigue. However, given that the differences in kinematics we could foresee as a result of manipulating the direction gaze were not dra- matic, we choose to try to minimize the effect of fatigue. Three minutes of recovery was afforded between each set of 5 repetitions.

A Panasonic WV-D5100HS SVHS video camera (Pan- asonic, Secaucus, NJ) operating at 60 Hz and with a shut- ter speed of 1/250 second was positioned 5.5 m to the right of the subject and was used to record each trial. The cam-

DIRECTION OF GAZE IN THE SQUAT 147

FIGURE 1. Reflective marker locations and angle designations.

TABLE 1. Mean total linear displacement of the bar and hip.*

Condition

Downward gaze Straight gaze Upward gaze

Mean total horizontal displacement of the bar (m) 0.12 0.11 0.10 SD 0.04 0.05 0.04 Mean total vertical displacement of the bar (m) 0.75 0.74 0.73 SD 0.08 0.09 0.08 Mean total horizontal displacement of the hip (m) 0.14 0.14 0.13 SD 0.02 0.02 0.03 Mean total vertical displacement of the hip (m) 0.39 0.38 0.38 SD 0.08 0.08 0.08

* Results were not statistically significant.

era was level, 90 cm from the floor, and was oriented with its optical axis perpendicular to a subject’s sagittal plane of motion. The camera was equipped with a halogen flood lamp that illuminated reflective markers on the subject. As illustrated in Figure 1, the reflective markers were located (a) just below the superciliary arch near the right eye, (b) at the greater trochanter of the right hip, (c) at the lateral articulation of the right knee, (d) at the lateral malleolous of the right ankle, and (e) at the end of the squatting bar.

The third trial from each set of 5 repetitions was dig- itized using a motion measurement system from Peak Performance Inc (Vicon-Peak, Centennial, CO). Thus, 6 trials were digitized for each subject (2 for each condi- tion), for a total of 60 trials. The landmarks denoted by

the reflective markers were automatically digitized begin- ning with the video frame displaying the first downward movement of the bar, and continued for each of 176 con- secutive frames (2.93 seconds). Once digitizing was com- pleted, the data was smoothed using a Butterworth dig- ital filter, and the dependent variables were computed.

Statistical Analyses

Variables included the linear displacement of the bar and hip, linear velocity of the bar, and the angular displace- ment/position and velocity of the head, trunk, hip, and knee (refer to Figure 1 for angle designations). To ascer- tain whether there were differences among the 3 condi- tions, the mean data were subjected to a repeated mea- sures analysis of variance (ANOVA), and where appro- priate, pairwise comparisons using Tukey’s Studentized Range Test. The correlation between the direction of gaze and mean head position was computed using a Spear- man’s rho (rank) correlation. An alpha level of 0.05 was used for the statistical tests.

RESULTS Linear Kinematics of the Bar and Hip

As shown in Table 1, a repeated measures ANOVA failed to reveal differences in the mean total horizontal and ver- tical bar displacements or the mean total horizontal and vertical hip displacements: F(2, 9) 5 0.81, p . 0.05; F(2, 9) 5 1.18, p . 0.05; F(2, 9) 5 0.77, p . 0.05; and F(2, 9) 5 0.87, p . 0.05, respectively. As is evident from the data presented in Table 2, there were likewise no significant differences in peak linear velocity of the bar in the down- ward, upward, forward, or backward directions: F(2, 9) 5 0.74, p . 0.05; F(2, 9) 5 0.53, p . 0.05; F(2, 9) 5 1.04, p . 0.05; and F(2, 9) 5 0.41, p . 0.05, respectively. The lack of differences in the data characterizing horizontal (i.e., anterior-posterior) motion indicates that postural sway, and thus stability, was not affected by the direction of gaze.

Angular Kinematics

The mean angular head position was computed to deter- mine the extent to which the different gaze conditions influenced head position. The mean head angles are shown in Table 3. The repeated measures ANOVA for head angle was significant (F[2, 9] 5 35.77, p , 0.0001). Pairwise comparisons using Tukey’s Studentized Range Test revealed significant differences between condition D and each of the other conditions (S: difference 5 22.72, 95% confidence limits [CL] 5 13.02, 32.42; U: difference 5 31.05, 95% CL 5 21.35, 40.75). However, the difference

148 DONNELLY, BERG, AND FISKE

TABLE 2. Mean peak linear velocity of the bar for 3 gaze directions.*

Condition

Downward gaze Straight gaze Upward gaze

Mean peak velocity of the bar in downward direction (m·s21) 0.92 0.94 0.91 SD 0.15 0.13 0.14 Mean peak velocity of the bar in upward direction (m·s21) 1.06 1.09 1.08 SD 0.09 0.08 0.10 Mean peak velocity of the bar in forward direction (m·s21) 0.15 0.15 0.13 SD 0.04 0.06 0.04 Mean peak velocity of the bar in backward direction (m·s21) 0.16 0.15 0.16 SD 0.05 0.06 0.07

* Results were not statistically significant.

TABLE 3. Mean maximum angular displacement of the trunk, hip, knee, and mean angular position of the head for 3 gaze directions.*

Condition

Downward gaze Straight gaze Upward gaze

Mean maximum trunk flexion† (8) 217 213 212 SD 7 12 12 Mean maximum hip flexion‡ (8) 77 84 86 SD 7 15 14 Mean maximum knee flexion (8) 82 83 85 SD 11 12 12 Mean head angle§ (8) 97 75 66 SD 12 5 10

* For the trunk and head, larger values represent greater flexion. For the hip and knee, smaller values represent greater flexion. See Figure 1 for angle designations.

† P 5 0.07. ‡ p , 0.05 (pairwise comparisons revealed a single significant difference between conditions D and U). § p , 0.0001 (pairwise comparisons revealed significant differences between conditions D and S, and D and U).

between conditions S and U did not achieve significance (difference 5 8.33, 95% CL 5 21.37, 18.03). The corre- lation coefficient between direction of gaze and mean head position was 0.79 (p , 0.0001). The results indicate that although direction of gaze and head position were strongly related, they should not be considered equiva- lent.

Also apparent in Table 3 is the fact that mean maxi- mum trunk, hip, and knee flexion were each greatest when the direction of gaze was directed downward (con- dition D). (Note that for the trunk, larger values repre- sent greater flexion, whereas for the hip and knee, small- er values represent greater flexion.) The repeated mea- sures ANOVA for mean maximum hip flexion was signif- icant (F[2, 9] 5 4.82, p , 0.05), with the lone significant difference found between conditions D and U. In other words, hip flexion was more severe when using the down- ward gaze than the upward gaze (difference 5 8.32, 95% CL 5 1.05, 15.58). The repeated measures ANOVA for mean maximum trunk flexion approached significance (F[2, 9] 5 3.02, p 5 0.07), with condition D exceeding both conditions S and U by 4 and 58, respectively. In other words, trunk flexion demonstrated a tendency to be more severe when using the downward gaze than when using the straight or upward conditions, but the difference was not statistically significant. The repeated measures AN- OVA for mean maximum knee flexion was not significant (F[2, 9] 5 0.48, p . 0.05), indicating that knee flexion was unaffected by gaze direction.

As shown in Table 4, the repeated measures ANOVAs

failed to reveal statistically significant differences among conditions for peak trunk, hip, and knee flexion velocity: F(2, 9) 5 1.81, p . 0.05; F(2, 9) 5 0.15, p . 0.05; and F(2, 9) 5 0.28, p . 0.05, respectively. There were likewise no significant differences among conditions for peak trunk, hip, and knee extension velocity: F(2, 9) 5 0.58, p . 0.05; F(2, 9) 5 0.36, p . 0.05; and F(2, 9) 5 2.02, p . 0.05, respectively.

DISCUSSION The purpose of this study was to begin to address the lack of clarity about head position or gaze direction during the squat exercise. Based on current technical standards for performing the squat exercise, as well as theoretical im- plications of head position and direction of gaze on pos- tural stability, we hypothesized that a downward gaze (condition D) would result in a greater maximum trunk flexion, as well as greater instability as determined by the total anterior-posterior displacement of the bar and hip. Conversely, we anticipated that an upward and straight- ahead gaze (conditions U and S, respectively) would re- sult in similar linear and angular kinematics.

First, however, we evaluated the extent to which the direction of gaze and head position were equivalent. As expected, there was a strong relationship between direc- tion of gaze and mean head position, yet it was not perfect (r 5 0.79, R2 5 62.4%). Strength and conditioning profes- sionals should be aware of the lack of a one-to-one map- ping between direction of gaze and head position, and

DIRECTION OF GAZE IN THE SQUAT 149

TABLE 4. Mean peak angular velocity of the trunk, hip, and knee for three gaze directions.

Condition

Downward gaze Straight gaze Upward gaze

Mean peak trunk flexion velocity (8·s21) 45 42 40 SD 8 10 6 Mean peak hip flexion velocity (8·s21) 102 101 100 SD 15 15 13 Mean peak knee flexion velocity (8·s21) 111 108 107 SD 22 21 19 Mean peak trunk extension velocity (8·s21 46 46 44 SD 5 9 7 Mean peak hip extension velocity (8·s21) 114 116 117 SD 14 10 18 Mean peak knee extension velocity (8·s21) 113 116 122 SD 24 23 29

* Results were not statistically significant.

should develop instructional cues for the squat exercise accordingly. Because we directly manipulated only the gaze direction in this study, we will refer only to it in the discussion.

Our hypotheses that condition D would result in greater total anterior-posterior motion of the bar and hip (postural sway) were not supported. Likewise, mean peak linear velocity of the bar in the downward, upward, for- ward, or backward direction did not differ across condi- tions. In sum, based on measures of total bar and hip displacement, as well as peak bar velocity, we must con- clude that direction of gaze did not influence postural sway, and thus stability, in the squat exercise.

Mean maximum trunk flexion was an average of 4.58 greater in condition D than in condition S or U. The sta- tistical analysis on this variable approached significance (p 5 0.07) and thus there is reason to believe that the downward gaze did result in greater trunk flexion than did conditions U and S. Moreover, under condition D, mean maximum hip flexion was 9 and 78 greater than conditions U and S, respectively, with the difference be- tween D and U achieving statistical significance. It is noteworthy that squat depth did not differ among condi- tions (as shown in Table 1—vertical displacement of the hip), nor did maximum knee flexion differ, indicating that the increase in hip flexion observed in condition D was not offset by greater knee flexion (i.e., a deeper squat).

Our findings appear to confirm the efficacy of the rec- ommendation made by some strength and conditioning professionals against allowing the head and eye focus to drop below a neutral position as a means of preventing excessive trunk flexion (3). What are the implications of greater trunk flexion in the squat? Of course, some trunk flexion is necessary, but excessive flexion could put an increased torque on the lower back musculature, possibly putting the athlete at greater risk of injuries such as mus- cle strains, disc herniations, and spondylolysis (stress fracture of the vertebral column) (3, 5, 14, 15). The injury risk that is speculated to accompany excessive trunk flex- ion resulting from a downward gaze might be exacerbated if accompanied by a concomitant increase in flexion ve- locity. However, analyses failed to reveal statistically sig- nificant differences among conditions for peak trunk flex- ion velocity.

Our study had 2 noteworthy limitations. First, sub- jects in the study were all college football players with a minimum of 1 year of experience performing the squat

exercise. Therefore, the results should not necessarily be generalized to younger athletes or those with less expe- rience performing the squat. Second, subjects performed the squat using 25% of their 1RM. It is possible that the effect of gaze direction on movement kinematics could dif- fer from that observed in this study when using a higher intensity exercise. This question will need to be addressed in future research, but for now we must emphasize that the results of this study apply only to low-intensity squat- ting. It is also important to emphasize that the significant and nearly significant differences in mean maximum hip and trunk flexion, respectively, were found between con- ditions D and U only. Thus, it is important to be precise in our conclusion that the downward gaze resulted in greater hip and trunk flexion than the upward gaze, but not greater than the straight gaze.

PRACTICAL APPLICATIONS

This study of male collegiate football players revealed overall similarity in movement kinematics when perform- ing the squat exercise using 3 different gaze directions: upward, straight, and downward. Our study was unable to differentiate between the straight and upward gaze di- rections. Conversely, the downward gaze was shown to increase the extent of hip flexion and possibly trunk flex- ion as well, especially relative to the upward gaze. Be- cause excessive hip and trunk flexion in the squat are contraindicated, cautioning athletes against allowing the head or direction of gaze to drop below a neutral position appears to be warranted.

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Acknowledgments

We would like to thank Michael Hughes for his contribution to this study.

Address correspondence to William P. Berg, bergwp@ muohio.edu.