Table 1 Population information of the included studies

Population

PD patients (excluding PD freezers and PD non-freezers)

3/21

[57,58,59]

PD freezers

9/21

[60,61,62,63,64,65,66,67,68]

PD non-freezers

7/21

[60, 61, 63, 65,66,67,68]

Stroke patients

4/21

[69,70,71,72]

Healthy older adults

13/21

[58, 60, 62, 63, 65, 67, 68, 71,72,73,74,75,76]

Middle-aged adults

2/21

[74, 75]

Young adults

2/21

[74, 77]

People with multiple sclerosis

1/21

[75]

Frail older adults

1/21

[73]

Pre-frail older adults

1/21

[73]

Older adults—multiple fallers

1/21

[76]

Older adults—single-fallers

1/21

[76]

Number of subjects

 < 20

2/21

[59, 77]

20–40

7/21

[57, 58, 64, 70,71,72, 76]

40–60

5/21

[60, 61, 63, 65, 66]

60–100

5/21

[62, 67, 69, 74, 75]

 > 100

2/21

[68, 73]