1. Introduction
Originally proposed for pre-season screening in elite athletes, the Upper Quarter Y-Balance Test (UQYBT) is a physical performance test increasingly used by trainers and clinicians, believed to investigate shoulder functions like stability, mobility, proprioception or strength (Bullock et al. Citation2017). While the participant stands in one-handed push up position, the other hand has to reach maximal distance in medial, inferolateral and superolateral directions. Main outcomes measures of UQYBT are distances, composites distances and score, which have been validated statistically (Westrick et al. Citation2012; Degot, Blache, Neyton, et al. Citation2019). No study has however identified the key neuromuscular features required to achieve the UQYBT performance. In consequence, in-depth analysis of the forces produced by the stance upper limb may contribute to better identify the strategy developed by athletes to reach maximal distances in the three directions.
The purpose of this study was therefore to assess ground reaction force (GRF) components exerted by the stance upper limb when performing UQYBT.
2. Methods
Four right-handed male athletes (age: 25.7 ± 5.5 years; height: 177.7 ± 4.8 cm; mass: 72.7 ± 10.2 kg; weekly training: 5.0 ± 3.5 hours; sports: running (n = 2), track and field (n = 1), crossfit (n = 1)) participated in this preliminary study, which was approved by the local ethical committee. Inclusion criteria were being 18-35 years-old and having declared no upper-limb troubles at the time of the study. Exclusion criteria were having undergone shoulder surgery or sustaining any injury at the upper limbs in the past six months preceding the study.
GRF signals of the stance limb were collected using a force plate (Kistler Biomechanics, model 9286B; 200 Hz). For motion analysis, one reflective marker was placed on the distal part of third metacarpus of each participant’s hand. Three additional reflective markers were fixed on boxes of the YBT Kit (Move2Perform, Evansville, IN, USA) intended to be moved by the subject. Marker trajectories were recorded using a 10-camera motion analysis system (Qualisys™, Sweden; 200 Hz).
After a standardized warm up (Degot, Blache, Vigne, et al. Citation2019), participants performed UQYBT using YBT Kit, with the stance hand resting onto the force plate. The participant stood in one-handed push up position with feet at shoulder width apart and extended elbow. He was instructed to push boxes with the free hand, as far as possible in medial (M), then inferolateral (IL), and finally superolateral (SL) directions. The right side was assessed first. After completing one familiarization trial, three maximal trials were performed per upper limb, with 30-s recovery between trials.
For each UQYBT direction, the motion was split into two phases, namely a first phase from the beginning to the end of one box displacement, and a second phase from the end of one box displacement to the beginning of the following box displacement.
For each phase in each direction, GRF was normalized by the participant’s body mass. The direction of the force in the horizontal plane was computed as the arctangent of the anteroposterior and mediolateral force components (). Then, the mean angle value was computed for each phase. Finally, GRF intensity was assessed by computing the mass-normalized magnitude of the force vector in the horizontal plane for each of the six phases. Angles and force magnitudes were then averaged for the three trials of each side.
Figure 1. Ground reaction force reference system and example of force direction represented by XY angle, for a trial with the right stance limb.
3. Results and discussion
Mean vertical force recorded during UQYBT phases for the dominant stance limb was 6.35 ± 0.41 N/kg, which was similar to those for the non-dominant limb (6.35 ± 0.37 N/kg), corresponding to about 65% of bodyweight as reported for unilateral push-up position (Uhl et al. Citation2003). Higher vertical forces were recorded for the SL direction with 6.93 ± 0.10 N/kg and 6.89 ± 0.12 N/kg for the dominant and non-dominant sides respectively, suggesting that athletes transferred a higher proportion of their bodyweight, i.e., 70% on average, on the stance limb for SL direction.
Mean anteroposterior and mediolateral forces recorded during UQYBT trials was 11 times smaller than mean vertical force, with 0.55 ± 0.22 N/kg for the dominant limb and 0.64 ± 0.20 N/kg for the non-dominant limb (). For both the sides, anteroposterior and mediolateral forces were two times higher for the M and IL direction than SL one, indicating that reaching maximal distances in these directions required more active mediolateral and anteroposterior force generation.
Table 1. Mean (± standard deviation) XY force intensities and directions in the medial (M), inferolateral (IL), superolateral (SL) directions, for the first phase (1) and second phase (2) and for the dominant (D) and non-dominant limb (ND).
Mean XY angles recorded during UQYBT trials for the sixth phases were 76.2 ± 10.0°, for the dominant side and 81.9 ± 2.6° for the non-dominant one. These outcomes indicated that, on the horizontal plane, the stance limb pushed mainly toward subject’s feet and medially, i.e., infero-medial force.
For the non-dominant stance limb in the three directions, little variations were observed for the mean XY angle orientation, revealing a single main force direction. For the dominant side, force orientations were similar for the M and IL directions; smaller angular values were however recorded for the superolateral phases, with a mean decrease of 15°. Such results may be explained by the higher inter-individual variability observed, indicating that orientation of the force may vary across the participants. These XY angle variations observed for the two SL phases however occurred since anteroposterior and mediolateral force intensity strongly decreased, i.e., 2.5 times lower, meaning that participants mainly pushed vertically to the horizontal plane. It then appears that various strategies may be selected by subjects to reach maximal distances in SL direction.
4. Conclusions
The main findings of this study on the GRF components revealed that UQYBT performance may be partly explained by the athlete capacity to maintain a high proportion of his bodyweight on the stance limb and to produce an inferomedial force to counteract instability generated by the moving upper limb. Considering the various strategies observed to reach the maximal superolateral distance in our sample, further analysis should be conducted to explore the underlying neuromuscular mechanisms in this direction.
This preliminary descriptive study contributes to a better understanding of the features of UQYBT performance and construct validity of the UQYBT. It can serve as a baseline for further studies by helping the identification of agonist/antagonist muscles of the shoulder complex during the UQYBT.
References
- Bullock GS, Brookreson N, Knab AM, Butler RJ. 2017. Examining fundamental movement competency and closed-chain upper-extremity dynamic balance in swimmers. J Strength Cond Res. 31(6):1544–1551.
- Degot M, Blache Y, Neyton L, Rogowski I. 2019. Intersession reliability of the Upper Quarter Y balance test score. Comput Methods Biomech Biomed Engin. 22:S264–S266.
- Degot M, Blache Y, Vigne G, Juré D, Borel F, Neyton L, Rogowski I. 2019. Intrarater reliability and agreement of a modified Closed Kinetic Chain Upper Extremity Stability Test. Phys Ther Sport. 38:44–48.
- Uhl TL, Carver TJ, Mattacola CG, Mair SD, Nitz AJ. 2003. Shoulder musculature activation during upper extremity weight-bearing exercise. J Orthop Sports Phys Ther. 33(3):109–117.
- Westrick RB, Miller JM, Carow SD, Gerber JP. 2012. Exploration of the y-balance test for assessment of upper quarter closed kinetic chain performance. Int J Sports Phys Ther. 7(2):139–147.