Effectiveness and usability of real-time vibrotactile feedback training to reduce postural exposure in real manual sorting work

Figures & data

Figure 1. (A) Conceptual description of the Smart Workwear System vibrotactile feedback module including an IMU, a vibration unit, a smartphone device with the smartphone application. The black arrows indicate the data or feedback signal flow, and the white block arrows illustrate the wireless (Bluetooth) communication flow. (B) Photo of the system vibrotactile feedback module showing an IMU, a vibration unit, and the smartphone application ErgoRiskLogger. (C) Photo of the system on a person.

(A) A conceptual description of the information flow from the postures of the wearer that are picked up by the IMU and sent to a smartphone device that analysis the information and provides feedback via a vibration unit. (B) A photo showing the smartphone device, the IMU and the vibration unit. (C) A photo showing a person wearing the Smart Workwear t-shirt and locations of the IMU and the vibration unit.

Table 1. The number of participants (n = 15) reporting musculoskeletal complaints and work-disabling musculoskeletal complaints (in parentheses) during the last 12 months at baseline.

	Never	Seldom once or several times a year	Sometimes once or several times a month	Most of the time once or several times a week	Always almost every day
Neck	6 (15)	5 (0)	4 (0)	0 (0)	0 (0)
Shoulders	7 (15)	5 (0)	3 (0)	0 (0)	0 (0)
Elbows	10 (15)	3 (0)	1 (0)	1 (0)	0 (0)
Wrists/hands	6 (14)	6 (0)	2 (1)	0 (0)	1 (0)
Upper back	5 (14)	5 (0)	4 (0)	1 (1)	0 (0)
Lower back	4 (12)	4 (1)	2 (1)	3 (1)	2 (0)
Hip	12 (15)	2 (0)	0 (0)	1 (0)	0 (0)
Knees	9 (13)	2 (1)	1 (0)	3 (1)	0 (0)
Ankles/feet	6 (13)	5 (0)	1 (2)	3 (0)	0 (0)

Figure 2. Photos displaying a typical work cycle comprising of sorting and scanning of packages arriving in a metal container (A–E), placing and scanning the packages in a destination (cardboard) container (F–G), and pushes the container to a conveyor belt (H–J).

Ten photos showing a typical work cycle. Photo (A–E) in the upper row, a worker wearing the Smart Workwear System is sorting and scanning a package in a metal container. Photo (F–G) in the left bottom row, the same person places and scans the package in a destination container. Photo (H–J) in the right bottom row, the same person manually transports the container using a trolley to its destination.

Figure 3. Illustration of the study setting. Five measurement days were performed, including the baseline, feedback training session 1, feedback training session 2 and post-training session (on the same day), and follow-ups 1 and 2. Surveys were collected on all measurement days with specific topics as illustrated in the boxes under each measurement day.

An illustration of the study setting comprising the baseline, feedback training session 1, feedback training session 2, and post-training session and follow-ups 1 and 2. For each occasion, the measurements used are described.

Figure 4. (A) Accumulated proportion of time of trunk forward inclination ≥30°, ≥45°, and ≥60° at baseline, the feedback training sessions 1 and 2, post-training session, and the follow-up sessions 1 and 2. (B) the 90th, 95th and 99th percentile trunk inclination angles, and the 10–90^th percentile range for trunk inclination. Statistically significant (p < 0.05, Wilcoxon signed-rank test) differences between the scenarios are displayed with their corresponding p-values.

(A) A boxplot showing the accumulated proportion of time of trunk forward inclination ≥30°, ≥45°, and ≥60° at baseline, the feedback training sessions 1 and 2, post-training session, and the follow-up sessions 1 and 2. (B) A boxplot showing the 90th, 95th and 99th percentile trunk inclination angles, and the 10–90th percentile range for trunk inclination at baseline, the feedback training sessions 1 and 2, post-training session and the follow-up sessions 1 and 2.

Table 2. Group median values and median intra-individual percentage differences (diff) (compared to the baseline) in the proportion of time in trunk inclination ≥30°, ≥45°, and ≥60°, and the group 90th, 95th, and 99th percentile angles and 10th–90th percentile range of trunk forward inclination in the feedback training sessions 1 and 2, the post-feedback training and the follow-up sessions 1 and 2.

	Baseline	Feedback training 1			Feedback training 2			Post-feedback training			Follow-up 1			Follow-up 2
	Median	Median	diff (%)	p-value	Median	diff (%)	p-value	Median	diff (%)	p-value	Median	diff (%)	p-value	Median	diff (%)	p-value
Trunk inclination (%)
≥30°	10.7	10.6	−13	0.192	4.2	−68	0.001	3.4	−60	<.001	8.3	−15	0.783	9.3	−7	0.680
≥45°	3.7	2.3	−34	0.015	1.2	−80	<.001	0.7	−61	0.002	2.5	−3.4	0.946	2.3	−33	0.394^w
≥60°	1.0	0.3	−80	0.026	0.2	−89	0.001^w	0.1	−67	0.034	0.8	−4.6	0.816	0.6	−44	0.339
Trunk inclination (°)
90th	30.7	30.7	−6.0	0.273	21.4	−34	0.002	19.3	−34	0.002	27.9	−12	0.623	28.8	−5.5	0.986
95th	42.0	40.0	−17	0.026	28.6	−29	<.001	26.8	−31	0.001	37.3	−13	0.290	35.7	−10	0.449
99th	60.2	49.7	−11	0.033	47.2	−36	<.001	40.1	−23	0.003	58.4	1.7	0.251	57.3	−11	0.178
10th–90th	32.1	27.4	−7.9	0.011	24.4	−31	<.001	19.7	−31	<.001	29.1	−2.4	0.598	29.2	0.1	0.570^w

The p-values display the difference in the proportion of time and inclination angles of the feedback training sessions, post-training session, and follow-up sessions compared to the baseline, using paired t-test and Wilcoxon signed-rank test. Significant differences (p < 0.05) are displayed in bold. Wilcoxon signed-rank test results are marked with w.

Table 3. Median (IQR) ratings of the 21-point Comfort Rating Scale with verbal anchors at each end: ‘Low’ (0), and ‘High’ (20).

Wearable comfort			Median (IQR) ratings
dimensions	Description	Wording of questions	Follow-up 1	Follow-up 2
Emotion	Emotions, concerns about appearance and relaxation	I am worried about how I look when I wear this device. I feel tense or on edge because I am wearing the device.	0.0 (0.0)	0.0 (0.0)
Attachment	Physical feel of the device on the body, attachment	I can feel the device on my body. I can feel the device moving.	5.0 (9.0)	0.0 (7.0)
Harm	Physical effect, damage to the body	The device is causing me some harm. The device is painful to wear.	0 .0 (0.0)	0.0 (0.0)
Perceived change	Feeling physically different, upset	Wearing the device makes me feel physically different. I feel strange wearing the device.	0 .0 (0.0)	0.0 (0.0)
Movement	The device physically affects movement	The device affects the way I move. The device inhibits or restricts my movement.	0.0 (8.5)	2.0 (5.0)
Anxiety	Worry about the device, safety, and reliability	I do not feel secure wearing the device.	0.0 (0.0)	0.0 (0.0)