Table 1.

Study summary for the step width variability during walking in young and older adults

Author / Year	Sample size	Exposure	Preferred walking speed protocol	Step width calculation	Step width variability / analyzed steps (avg.)
Almarwani et al. (2016a) [39]	OA, n = 111 (82 f), age = 77.25 ± 6.0 yr., ht. = 163.4 ± 9.5 cm, wt. = 77.4 ± 15.7 kg; YA, n = 40 (30 f), age = 26.60 ± 6.0 yr., ht. = 168.4 ± 8.3 cm, wt. = 66.4 ± 12.4 kg	Walking on a 4 m walkway in 3-speed conditions	Participants were instructed to walk at a pace that represented their usual walking speed. OA, PWS = 1.07 ± 0.26 m/s; YA, PWS = 1.29 ± 0.19 m/s.	The distance between the outermost borders of two consecutive footprints (GaitMat II).	OA: 3.70 ± 1.80 cm; YA: 2.40 ± 0.60 cm. OA: 23 steps YA: 38 steps
Almarwani et al. (2016b) [40]	OA, n = 46 (35 f), age = 78.09 ± 6.2 yr., ht. = nr cm, mass = nr kg; YA, n = 40 (30 f), age = 26.6 ± 6.0 yr., ht. = nr cm, mass = nr kg;	Walking on an 8 m walkway at preferred speed	Authors did not describe how the preferred walking speed was determined. OA, PWS = 0.95 ± 0.28 m/s; YA, PWS = 1.29 ± 0.19 m/s.	The distance between the outermost borders of two consecutive footprints (GaitMat II).	OA: 3.00 ± 1.41 cm; YA: 2.50 ± 1.41 cm OA: 23 steps YA: 38 steps
Decker et al. (2016) [41]	OA, n = 19 (9 f), age = 69.26 ± 1.11 yr., ht. = 171 ± 2 cm, mass = 77.45 ± 2.78 kg; YA, n = 20 (12 f), age = 24.45 ± 0.87 yr., ht. = 173 ± 2 cm, mass = 70.41 ± 2.63 kg	Three-minutes treadmill walking at 4 attentional demands conditions at a preferred speed	Participants started walking at a slow speed while the treadmill was slowly accelerated by 0.1 km/h until the participants reported their PWS. Then the speed was increased by 1.5 km/h and was slowly decreased by 0.1 km/h until the participants reported their PWS. This procedure was repeated until a less than 0.4 km/h difference was achieved. OA, PWS = 0.77 ± 0.04 m/s; YA, PWS = 1.06 ± 0.03 m/s.	Mediolateral distance between foot midpoints calculated over the consecutive instants when the left (or right) swing limb’s knee passed in front of the right (or left) stance limb’s knee	OA: 1.70 ± 0.17 cm; YA: 1.92 ± 0.08 cm OA: ≥ 256 steps YA: ≥ 256 steps
Ihlen et al. (2012) [42]	OA, n = 10 (4 f), age = 75.4 ± 4.6 yr., ht. = 170.9 ± 11.8 cm, mass = 76 ± 13.1 kg; YA, n = 10 (4 f), age = 25.7 ± 4.7 yr., ht. = 177.6 ± 8.3 cm, mass = 74.5 ± 9.5 kg	Ten-minutes treadmill walking in 3-speed conditions	Authors did not describe how the preferred walking speed was determined. OA, PWS = 1.17 ± 0.10 m/s; YA, PWS = 1.11 ± 0.15 m/s.	Step width was defined as the mediolateral distance between heel markers at the time of heel strike	OA: 2.55 ± 0.35 cm; YA: 1.91 ± 0.30 cm OA: nr steps YA: nr steps
Kang et al. (2008) [43]	OA, n = 18 (6 f), age = 72.1 ± 6.0 yr., ht. =170 ± 10.4 cm, mass = 73.2 ± 12.3 kg; YA, n = 17 (5 f), age = 23.6 ± 2.6 yr., ht. = 173 ± 9.4 cm, mass = 71.1 ± 9.86 kg	Five-minutes treadmill walking in 5-speed conditions	Participants reported the limits of their preferred speed while the treadmill was slowly accelerated, then decelerated three times. These upper and lower limits were averaged to determine their preferred walking speed. OA, PWS = 1.29 ± 0.15 m/s; YA, PWS = 1.30 ± 0.10 m/s.	Step width was defined as the distance between the heel and the contralateral heel at each heel contact in the mediolateral direction	OA: 2.14 ± 0.54 cm; YA: 2.01 ± 0.56 cm OA: nr steps YA: nr steps
Lovden et al. (2008) [38]	OA, n = 32 (16 f), age = 73.6 ± 2.9 yr., ht. = 169.4 ± 10 cm, mass = 74.3 ± 11.5 kg; YA, n = 32 (16 f), age = 25.0 ± 2.9 yr., ht. = 177.6 ± 9.8 cm, mass = 71.6 ± 13.1 kg	Twenty-secs treadmill walking in 4 conditions of working memory load at a preferred speed	Participants gradually increased speed to determine preferred walking speed. After walking at their self-selected speed for 3 min were asked again if they felt comfortable with their choice. OA, PWS = 0.87 ± 0.13 m/s; YA, PWS = 1.04 ± 0.11 m/s.	The step width was measured as the perpendicular distance between the line of progression and the heel location of the contralateral foot.	OA: 2.19 ± 0.11 cm; YA: 1.97 ± 0.12 cm OA: 18 steps YA: 18 steps
Marigold et al. (2008) [44]	OA, n = 10 (5 f), age = 74.1 ± 7.2 yr., ht. = nr cm, mass = nr kg; YA, n = 10 (5 f), age = 26.1 ± 5.2 yr., ht. = nr cm, mass = nr kg	walking on a multi-surface terrain in 4 different terrain configurations for YA and in 3 different conditions for OA, respectively, at a preferred speed	Authors did not describe how the preferred walking speed was determined. OA, PWS = 1.20 ± 0.12 m/s; YA, PWS = 1.32 ± 0.16 m/s.	The mediolateral distance between ankle markers	OA: 4.09 ± 0.70 cm; YA: 2.96 ± 1.29 cm OA: nr steps YA: nr steps
Owings et al. (2004a) [45]	OA, n = 12 (nr), age = 73.4 ± 2.3 yr., ht. = 172 ± 13 cm, mass = 76.3 ± 15.5 kg; YA, n = 18 (nr), age = 27.7 ± 3.3 yr., ht. = 168 ± 11 cm, mass = 35.9 ± 10.2 kg	Ten-minutes treadmill walking for OA and 15-min for YA at a preferred speed	Authors did not describe how the preferred walking speed was determined. OA, PWS = 0.97 ± 0.17 m/s; YA, PWS = 1.06 ± 0.28 m/s.	Step width was determined as the mediolateral distance between the sequential left and right heel-strikes	OA: 2.50 ± 0.70 cm; YA: 2.10 ± 0.50 cm OA: nr steps YA: nr steps
Paterson et al. (2009) [46]	OA, n = 32 (32 f), age = 67.4 ± 6.3 yr., ht. = 162 ± 7 cm, mass = 65.1 ± 13.2 kg; YA, n = 22 (22 f), age = 21.2 ± 2.5 yr., ht. = 166 ± 8 cm, mass = 62.6 ± 9.8 kg	10 m continuous laps of a walking circuit at a preferred speed	Authors did not describe how the preferred walking speed was determined. OA, PWS = nr; YA, PWS = nr.	The midline midpoint of the current footprint to the midline midpoint of the previous footprint on the opposite foot (GaitRite).	OA: 2.50 ± 0.83 cm; YA: 1.90 ± 0.83 cm OA: nr steps YA: nr steps
Thies et al. (2005) [47]	OA, n = 12 (12 f), age = 70.2 ± 4.1 yr., ht. = nr cm, mass = nr kg; YA, n = 12 (12 f), age = 22.2 ± 3.0 yr., ht. = nr cm, mass = nr kg,	Walking on a 10 m walkway in 4 task conditions at a preferred speed	Subjects were asked throughout the experiment to walk at a comfortable speed as if they were going to mail a letter. OA, PWS = 1.15 ± 0.06 m/s; YA, PWS = 1.08 ± 0.06 m/s.	Mediolateral distance between the left and right foot ankle (tibiotalar joint) markers during double support	OA: 2.99 ± 0.20 cm; YA: 2.50 ± 0.17 cm OA: 55 steps YA: 63 steps
Woledge et al. (2005) [48]	OA, n = 21 (8 f), age = 72.7 ± 1.21 yr., ht. = 166 ± 2 cm, mass = 68.3 ± 2.6 kg; YA, n = 17 (11 f), age = 27.3 ± 1.5 yr., ht. = 171 ± 2 cm, mass = 64.3 ± 2.9 kg	Walking on 8 m walkway at a preferred speed	Authors did not describe how the preferred walking speed was determined. OA, PWS = 1.12 ± 0.06 m/s; YA, PWS = 1.19 ± 0.03 m/s.	The lateral difference between successive footfall positions (medial malleoli)	OA: 2.32 ± 0.28 cm; YA: 1.73 ± 0.37 cm OA: 34 steps YA: 34 steps

Note. OA older adults; YA younger adults; PWS preferred walking speed; f females; nr not reported; n number; yr years; m/s meters per second; cm centimeters; avg average; ht height