Muscle Recruitment Strategies in a Redundant Task: Age Differences Through Network Analyses

Figures & data

Table 1. Age, mass and height per participant.

Young women
ID	Age (years)	Mass (kg)	Height (m)
1	19	58.0	1.57
2*	21	60.0	1.73
3	21	62.3	1.63
4	21	70.0	1.68
5	23	57.5	1.69
6	22	58.0	1.65
7	23	60.0	1.64
8	25	63.0	1.69
9	22	67.0	1.67
10	22	69.0	1.66
Old women
ID	Age (years)	Mass (kg)	Height (m)
1	60	78.6	1.71
2	69	58.0	1.56
3	60	72.8	1.59
4	73	58.4	1.67
5	62	52.9	1.62
6*	65	61.2	1.57
7	73	79.0	1.64
8	60	52.3	1.65
9	60	55.3	1.52
10	60	81.0	1.67

* Not included in the analysis due to faulty data.

Figure 1. Normalized muscle activation per group (average: bar height; 95% confidence interval: error bars) and per leg. Each blue bar represents individual average muscle activation over the 20 bouts of co-contraction. (RF: rectus femoris; VL: vastus lateralis; VM: vastus medialis; SAR: sartorius; ST: semitendinosus; SM: semimembranosus; BFL: biceps femoris long head; BFS: biceps femoris short head; TFL: tensor fascia latae).

Table 2. Descriptive measures (mean and standard deviation) of the peak torque (N.m) test and EMG (mean and standard deviation) per individual and leg.

	Peak torque (N.m)
	Right				Left
	Extension		Flexion		Extension		Flexion
Old	145.1 ± 31.2		57.6 ± 10.8		143.1 ± 30.1		54.8 ± 9.0
Young	221.8 ± 20.9		88.4 ± 20.7		205.6 ± 32.3		85.2 ± 19.0
	EMG (%)
	Right				Left
	B1	B2		B3	B1	B2		B3
Old	25.5 ± 8.8	28.6 ± 8.8		28.3 ± 8.7	29.8 ± 15.1	33.7 ± 15.8		33.5 ± 12.87
Young	39.4 ± 18.2	40.0 ± 7.1		37.6 ± 7.5	39.4 ± 11.1	37.2 ± 7.8		35.35 ± 6.54
	EMGvar (%)
	Right				Left
	B1	B2		B3	B1	B2		B3
Old	1.7 ± 1.5	2.2 ± 1.7		2.1 ± 1.1	2.4 ± 2.5	2.7 ± 2.5		3.3 ± 3.1
Young	3.7 ± 3.3	5.0 ± 1.5		4.6 ± 1.5	3.8 ± 2.3	2.8 ± 2.4		3.1 ± 2.8

B1: Block 1; B2: Block 2; B3: Block 3.

Figure 2. Magnitude squared coherences from 0 to 90 Hz for each muscle pair considering young (lower left) and old (upper right) women groups. The central line represents the average coherence between individuals and the shaded area represents the 95% confidence interval. (RF: rectus femoris; VL: vastus lateralis; VM: vastus medialis; SAR: sartorius; ST: semitendinosus; SM: semimembranosus; BFL: biceps femoris long head; BFS: biceps femoris short head; TFL: tensor fascia latae).

Figure 3. Exemplary network profiles (top row) for the extracted coherence profiles (bottom row) from the matched-frequency synergies analysis (see text). The thickness of the edges represents the magnitude of the relation (coherence) between nodes (muscles). The colors of nodes represent whether they are flexors (red), extensors (blue), or unrelated (purple). Edges below a given threshold are not shown (for illustration purposes).

Figure 4. Network measures (from matched-frequency synergies, see text) per group, leg, and synergies. The dots represent each individual.

Figure 5. Exemplary network profiles (odd rows) for the extracted coherence profiles (even rows) from the unmatched-frequency synergies analysis (see text). The thickness of the edges represents the magnitude of the relation (coherence) between nodes (muscles). The colors of nodes represent whether they are flexors (red), extensors (blue), or unrelated (purple). Edges below a given threshold are not shown (for illustration purposes).

Figure 6. Number of synergies extracted and the network measures (from unmatched-frequency synergies, see text) per group and leg averaged over synergies. The dots represent each individual.

Figure 7. Exemplary network profiles (left column), muscle loadings (center column) of the most prominent synergy, and these synergies’ contributions over time (right column) considering one young and one old woman. For the network profiles, the thickness of the edges represents the magnitude of the relation (absolute correlation) between nodes (muscles). The colors of nodes represent whether they are flexors (red), extensors (blue), or unrelated (purple). Edges below a given threshold are not shown (for illustration purposes). The contributions over time were plotted as a function of time and trials (see legend).

Figure 8. Number of synergies, participating muscles and synergy contribution per group, leg, and blocks. The dots represent each individual.

DATA AVAILABILITY STATEMENT

The data and codes are available at the Open Science Foundation website associated with the project (doi: 10.17605/OSF.IO/3YVSN)