Influence of Posture Variation on Shoulder Muscle Activity, Heart Rate, and Perceived Exertion in a Repetitive Manual Task

Figures & data

FIGURE 1 Participant performing the four experimental conditions A: H30/30, B: D20/40, C: V10/50, and D: H50/50.

FIGURE 2 An example illustrating the standard, adjustment, and steady state phases of the 60-minute pick-and-place task protocol.

FIGURE 3 Upper arm elevation variables for the four workstation designs at the standard pace: angle_MEAN (left), angle_SD (middle), and RoM (right). Lines show individual results for females (n = 5, red squares, solid lines) and males (n = 7, blue triangles, dashed lines); median values across all participants are marked by black circles.

TABLE 1 Median kinematic (n = 12) and EMG (n = 13) variables during the standard pace, with p-values obtained from the Friedman tests and from the post-hoc univariate Wilcoxon signed-rank tests.

	Median value					Univariate Wilcoxon signed-rank tests
Standardized pace (10 cycles·min^−1)	H30/30	D20/40	V10/50	H50/50	Friedman Main effect p-value	H30/30, D20/40	H30/30, V10/50	D20/40, V10/50	H30/30, H50/50	D20/40, H50/50	V10/50, H50/50
Upper arm elevation
anglemean (°)	36.6	35.5	34.2	46.4	<0.001^*	0.807	0.807	0.753	0.003^*	0.002^*	0.002^*
anglesd (°)	4.7	7.5	10.6	3.8	<0.001^*	0.004^*	0.001^*	0.001^*	0.530	0.003^*	0.002^*
RoM (°)	17.9	25.7	34.9	15.9	<0.001^*	0.004^*	0.002^*	0.002^*	0.583	0.002^*	0.002^*
vmean (°·s^−1)	16.8	19.9	24.9	14.7	<0.001^*	0.010	0.002^*	0.002^*	0.071	0.010	0.002^*
vpeak (°·s^−1)	67.2	95.2	112.8	64.2	<0.001^*	0.002^*	0.002^*	0.012	0.388	0.003^*	0.002^*
Dominant upper trapezius
RMSmean (% RVE)	46.9	48.8	63.1	94.0	0.002^*	0.221	0.028	0.463	0.003^*	0.041	0.209
RMSsd (% RVE)	15.6	26.6	37.3	26.5	<0.001^*	0.009	0.001^*	0.039	0.002^*	0.239	0.023
CV	0.42	0.50	0.58	0.34	<0.001^*	0.064	0.002^*	0.007^*	0.182	0.004^*	0.002^*
Non-dominant upper trapezius
CV	0.33	0.42	0.39	0.39	0.801	0.311	0.196	0.917	0.583	0.433	0.272
Dominant infraspinatus
CV	0.44	0.45	0.37	0.45	0.272	0.701	0.507	0.279	0.583	0.239	0.754
Dominant anterior deltoid
CV	0.50	0.50	0.48	0.47	0.296	0.600	0.101	0.311	0.875	0.239	0.012
Dominant medial deltoid
CV	0.56	0.63	0.60	0.49	0.018^*	0.133	0.196	0.382	0.050	0.005^*	0.005^*
Dominant extensor digitorum
CV	0.52	0.57	0.56	0.56	0.849	0.917	0.552	0.463	0.695	0.347	0.814
Cardiovascular response
HR (bpm)	68.4	68.0	71.0	70.0	0.840	0.722	0.534	0.790	0.333	0.721	0.285
RMSSD (ms)	33.8	32.9	35.0	37.3	0.516	0.131	0.182	0.657	0.203	0.445	0.241

* p < 0.05 (Friedman) and 0.00833 (Wilcoxon).

TABLE 2 Median MAWP and MTM pace for each workstation design, and ratings of perceived exertion (RPE; Borg CR-10) directly after the steady state phase, with p-values obtained from the Friedman test and from the post-hoc univariate Wilcoxon signed-rank tests.

	Median value					Univariate Wilcoxon signed-rank tests
	H30/30	D20/40	V10/50	H50/50	Friedman Main effect p-value	H30/30, D20/40	H30/30, V10/50	D20/40, V10/50	H30/30, H50/50	D20/40, H50/50	V10/50, H50/50
Pace
MAWP	11	10	10	9	0.030^*	0.803	0.782	0.480	0.066	0.021	0.034
MTM	122	118	118	103	0.030^*	0.906	0.609	0.588	0.068	0.013	0.068
RPE
Neck	3.5	3.0	2.0	2.5	0.382	0.271	0.441	0.811	0.368	0.886	0.752
Shoulder	3.5	3.0	3.0	3.5	0.447	0.366	0.510	0.726	0.755	0.287	0.312
Upper arm	1.5	2.0	2.5	2.5	0.067	0.214	0.230	0.941	0.012	0.071	0.108
Lower arm	2.0	1.0	1.5	2.0	0.121	0.161	0.492	0.856	0.258	0.589	1.000
Wrist	1.0	0.5	0.8	0.8	0.535	0.750	0.429	0.150	0.674	0.465	0.863

* p < 0.05 (Friedman) and 0.00833 (Wilcoxon).

FIGURE 4 Cumulative probability distribution of the maximal acceptable work pace for the four workstation designs.

FIGURE 5 Upper arm elevation variables for the four workstation designs at the MAWP: angle_MEAN (left), angle_SD (middle), and RoM (right). Lines show individual results for females (n = 4, red squares, solid lines) and males (n = 6, blue triangles, dashed lines); median values across all participants are marked by black circles.

TABLE 3 Median kinematic (n = 12, excepting n = 10 for H50/50) and EMG (n = 13, excepting n = 10 for H50/50) variables during the MAWP with p-values obtained from the Friedman's test and from the post-hoc univariate Wilcoxon signed-rank tests.

	Median value					Univariate Wilcoxon signed-rank tests
MAWP	H30/30	D20/40	V10/50	H50/50	Friedman Main effect p-value	H30/30, D20/40	H30/30, V10/50	D20/40, V10/50	H30/30, H50/50	D20/40, H50/50	V10/50, H50/50
Upper arm elevation
anglemean (°)	35.4	40.3	35.1	48.3	0.001^*	0.861	0.600	0.507	0.005^*	0.005^*	0.007^*
anglesd (°)	4.5	8.0	10.4	3.9	<0.001^*	0.004^*	0.001^*	0.002^*	0.241	0.007^*	0.005^*
RoM (°)	17.2	27.6	35.2	15.7	<0.001^*	0.003^*	0.002^*	0.010	0.386	0.005^*	0.005^*
vmean (°·s^−1)	15.7	20.1	24.4	13.9	<0.001^*	0.015	0.002^*	0.002^*	0.114	0.009	0.005^*
vpeak (°·s^−1)	66.8	100.1	112.6	66.8	<0.001^*	0.002^*	0.002^*	0.002^*	0.575	0.005^*	0.005^*
Dominant upper trapezius
RMSmean (% RVE)	47.1	59.8	56.2	77.9	0.029^*	0.507	0.023	0.701	0.013	0.241	0.445
RMSsd (% RVE)	22.4	29.4	37.0	27.8	<0.001^*	0.006^*	0.001^*	0.064	0.009	0.878	0.017
CV	0.42	0.48	0.61	0.38	0.004^*	0.011	0.005^*	0.033	0.445	0.028	0.007^*
Non-dominant upper trapezius
CV	0.38	0.43	0.37	0.37	0.187	0.382	0.075	0.753	0.508	0.386	0.241
Dominant infraspinatus
CV	0.46	0.48	0.49	0.47	0.356	0.552	0.753	0. 807	0.169	0.386	0.114
Dominant anterior deltoid
CV	0.49	0.49	0.55	0.52	0.253	0.221	0.011	0. 087	0.139	0.508	0.333
Dominant medial deltoid
CV	0.58	0.61	0.62	0.55	0.131	0.013	0.033	0. 650	0.445	0.059	0.047
Dominant extensor digitorum
CV	0.52	0.55	0.52	0.57	0.048^*	0.507	0.173	0. 463	0.074	0.203	0.169
Cardiovascular response
HR (bpm)	69.2	68.2	70.1	70.0	0.583	0.790	0.790	0.929	0.575	0.779	0.889
RMSSD (ms)	28.4	36.5	28.1	22.3	0.586	0.286	0.929	0.534	0.110	0.139	0.314

* p < 0.05 (Friedman) and 0.00833 (Wilcoxon).

FIGURE 6 EMG variables for the dominant upper trapezius muscle in the four workstation designs at the MAWP: RMS_MEAN (left), RMS_SD (middle), and CV (right). Lines show individual results for females (n = 4, red squares, solid lines) and males (n = 6, blue triangles, dashed lines); median values across all participants are marked by black circles.

Table

				TMU at different distances between central and distant target (cm)
	Action	Abbr.	Class.	12	12.5	13–15	15.5–17.5	18–20	20.5–22.5	23–25	25.5–27.5
1	Grasp	G	1C3	10.8	10.8	10.8	10.8	10.8	10.8	10.8	10.8
2a	Move	M	C	8.0	9.2	9.2	10.3	11.1	11.8	12.7	13.5
2b	Position	P	2	26.6	26.6	26.6	26.6	26.6	26.6	26.6	26.6
3	Release	RL	1	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0
4	Reach	RE	D	8.4	9.4	9.4	10.1	10.8	11.5	12.2	12.9
5	Grasp	G	1C3	10.8	10.8	10.8	10.8	10.8	10.8	10.8	10.8
6a	Move	M	C	8.0	9.2	9.2	10.3	11.1	11.8	12.7	13.5
6b	Position	P	2	26.6	26.6	26.6	26.6	26.6	26.6	26.6	26.6
7	Release	RL	1	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0
8	Reach^a	RE	D	12.2	12.2	12.9	14.2	15.6	17.0	18.4	19.8
9	Grasp	G	1C3	10.8	10.8	10.8	10.8	10.8	10.8	10.8	10.8
10	Move	M	C	8.0	9.2	9.2	10.3	11.1	11.8	12.7	13.5
11	Release	RL	1	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0
12	Reach	RE	D	8.4	9.4	9.4	10.1	10.8	11.5	12.2	12.9
13	Grasp	G	1C3	10.8	10.8	10.8	10.8	10.8	10.8	10.8	10.8
14	Move	M	C	8.0	9.2	9.2	10.3	11.1	11.8	12.7	13.5
15	Release	RL	1	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0
Total TMU				165.4	172.2	172.9	180.0	186.0	191.6	198.0	204.0
CT—MTM-100				6.0	6.2	6.2	6.5	6.7	6.9	7.1	7.3
WP—MTM-100				10.1	9.7	9.6	9.3	9.0	8.7	8.4	8.2
CT—MTM-110				5.4	5.6	5.7	5.9	6.1	6.3	6.5	6.7
WP—MTM-110				11.1	10.6	10.6	10.2	9.9	9.6	9.3	9.0
CT—MTM-120				5.0	5.2	5.2	5.4	5.6	5.7	5.9	6.1
WP—MTM-120				12.1	11.6	11.6	11.1	10.8	10.4	10.1	9.8

Note. The table shows MTM assessment of the task. The complete work cycle consisted of 15 separate actions with an abbreviation (Abbr.) and a classification (Class.) which, depending on the individually pre-set distance between middle and distant target, corresponds to a certain amount of time measurement units (TMU). The sum of the TMU per action is converted into the cycle time (CT) at MTM-100 (total TMU × 0.036 s) and into the work pace corresponding to MTM-100 (WP; 60 / CT). Additionally, the CT (s) and WP (cycles·min⁻¹) for MTM-110 and MTM-120 are provided.

^a Step number 8 in the work cycle included reach at the double distance from the one side target to the other.