**3. Results**

#### *3.1. Trunk Compensation*

For trunk flexion and trunk lateral flexion, the K2 was closer in magnitude to the VMC than the K1 in all directions and for both non-extended and extended reaches (Table 1). For trunk flexion, when considering Bland-Altman LOA for all movements, the K2 was within −3.5◦–6.6◦ and the K1 was within −2.7◦–14.2◦ of the VMC (Table A2). Similarly for trunk lateral flexion, the K2 was within −5.9–7.9◦ and the K1 was within −9.0–13.4◦ of the VMC. Significant di fferences were found between K2 and VMC for trunk flexion during extended forward reaching and lateral flexion during extended scaption reaching (Table 1). Significant di fferences were found between K1 and VMC for trunk flexion during all extended reaches and lateral flexion in all conditions but extended lateral reaching.

The K2 was more valid than the K1 for measuring trunk movements during extended reaches (Table 2). The K2 showed excellent agreemen<sup>t</sup> with the VMC for measuring trunk flexion (r = 0.77–0.88) and lateral flexion (r = 0.77–0.89) during extended reaches. The K1 showed moderate–excellent agreemen<sup>t</sup> with the VMC for trunk flexion (r = 0.52–0.78) and moderate agreemen<sup>t</sup> for lateral flexion (r = 0.50–0.60) during extended reaches. For non-extended reaches, the K2 showed only moderate agreemen<sup>t</sup> (r = 0.43) for measuring trunk flexion during lateral reaching. All other correlations were poor for both the K1 and K2. Bland-Altman analyses show that mean biases for trunk flexion and lateral flexion were smaller and with narrower LOA for the K2 than the K1 when compared to VMC (Table A2).

Reliability results were mixed for all three sensors when measuring the trunk (Table 3). The K2 showed excellent reliability for measuring trunk flexion during lateral reaching (ICC = 0.91), but poor–modest reliability for trunk flexion in all other reach directions (ICC = −0.53–0.69). The K2 also showed excellent reliability for lateral flexion in the scaption (ICC = 0.75), lateral (ICC = 0.82), and extended forward (ICC = 0.84) directions, but poor–modest reliability in all other directions (ICC = 0.12–0.66). The K1 showed modest–excellent reliability (ICC = 0.62–0.88) for trunk measurements during reaches in all directions except forward (ICC = 0.28–0.34). The VMC showed mixed results similar to K2, with poor–excellent reliability in the forward direction (ICC = −0.42–0.93), poor–excellent reliability in the scaption direction (ICC = 0.08–0.89), and modest–excellent reliability in the lateral direction (ICC = 0.66–0.82) for both trunk flexion and lateral flexion. Pearson's correlations between testing days mirror these results (Table A3). Bland-Altman LOA analyses show small

mean biases for trunk flexion and lateral flexion between testing days for the K1 (bias = −1.4◦–0.8◦), K2 (bias = −3.2◦–1.4◦), and VMC (bias = −3.0◦–1.8◦) (Table A4).

**Table 1.** Mean (± SD) magnitudes for the K1, K2, and VMC for all kinematic variables and all movements on the two different testing days D1 and D2. Each of five participants performed four sets of five reaches (N = 100) for each direction and condition. This sample was repeated on two separate testing days (D1 and D2).


*\* p* < 0.05 for Bonferonni-corrected pairwise *t*-test between Kinect and VMC. \*\* *p* < 0.05 for paired *t*-test between testing days. K1: KinectV1; K2: KinectV2; VMC: video motion capture; D1: day one of testing; D2: day two of testing.


**Table 2.** Validity measured by Pearson's correlation coefficients (r) between the K1 and VMC and the K2 and VMC on D1.

*\* p* < 0.05 for Pearson's correlation between Kinect and VMC. K1: KinectV1; K2: KinectV2; VMC: video motion capture; D1: day one of testing.



K1: Kinect V1; K2: KinectV2; VMC: video motion capture; D1: day one of testing; D2: day two of testing.

#### *3.2. Upper Extremity Movements*

The movement traces for the three planar reaching conditions (i.e., sagittal, scaption, frontal) illustrate directional differences between the Kinects and the VMC (Figure 3). Discrepancies in reaching magnitude between the Kinects and the VMC were dependent on the direction of movement. Differences in reaching ROM and planar distance were greatest during forward reaching, reduced during scaption reaching, and least during lateral reaching (Figure 3). Reaching ROM, planar reach distance, and elbow flexion measurements consistently showed excellent validity for the K2 (r = 0.79–0.99) and moderate–excellent validity for the K1 (r = 0.60–0.95) (Table 2). Reliability of these measurements was moderate–excellent for all three sensors (Table 3). Validity and reliability of shoulder flexion and abduction measurements varied from poor to excellent for all three sensors (Tables 2 and 3).

**Figure 3.** Three sets of curves showing reach ROM from start to stop of a typical reaching movement. The **left** curve (F) represents a forward reach, the **middle** curve (S) represents a scaption reach, and the **right** curve (L) represents a lateral reach. Curves for the K1, K2, and VMC are shown separately (see legend).
