The main results of this study can be summarized as follows: (i) The magnitude of variability in plantar pressure assessed by m.s.e. is disparate and observed between speeds, and between subjects (figure 1). All subjects expressed CV less than 2.5% (figure 1), which is less than that reported as ‘very low’ by standard measures of CV in biomechanics literature (less than 3%).(ii) RMA regression suggested positive linear trends in m.s.e. across walking speeds in 11 out of 16 subjects, and CV and speed in 15 out of 16 subjects (figure 1). R2 and p-values strongly support a linear increase in plantar pressure variability with speed when assessed by m.s.e. in 4 subjects, and in 11 subjects when assessed by CV (R2 > 0.5, p = <0.05) (table 2) (figure 1). Topological regression analysis of m.s.e. and speed confirmed no statistical support for a systematic linear increase in variability with speed (figure 2).(iii) RMA regression suggested positive linear relationships between m.s.e. and Froude number in 11 out of 16 subjects, and CV and Froude number in 15 out of 16 subjects (figure 3). However, R2 and p-values (R2 > 0.5, p = <0.05) only strongly support linear increases in variability with Froude number when assessed by m.s.e. in 4 subjects, but in 11 subjects when assessed by CV (table 2) (figure 3).(iv) Qualitative analysis of topological variation maps suggests that spatial distribution of m.s.e. is highest in the forefoot, specifically the lateral and medial margins, under metatarsal heads five and one, respectively, in all subjects, and is independent of speed (figure 4).(v) Qualitative analysis of topological variation maps suggests that the spatial distribution of CV is highest in the midfoot, medial phalanges, big toe and lateral margins of the heel in all subjects, and is independent of speed (figure 5). Figure 1.(a–p) RMA regression suggested positive linear trends in m.s.e. (y axis) across all walking speeds in 11 out of 16 subjects, and CV (z axis) and speed in 15 out of 16 subjects. However r2 and p-values only strongly support a linear increase in plantar pressure variability with speed in four subjects when assessed by m.s.e., but in 10 subjects when assessed by CV (r2 > 0.75, p = <0.05) (see table 2). Figure 2.(a–p) Linear regression by pSPM (left panel) reveals no statistical support for linear changes in variability by m.s.e. with speed. The left image is the inference map, showing areas of increasing or decreasing variability in pressure across the plantar surface. The red pixels indicate that variability is increasing with speed around the periphery of the heel and forefoot only. The blue pixels indicate that variability is decreasing with speed around periphery of the midfoot and occasionally the hallux. Statistically significant pixels are concentrated almost exclusively around the periphery of mechanically distinct areas of the foot, thus they are most probably artefacts of small changes in foot contact area, size and shape with speed. The mechanically distinct areas of the plantar surface, heel, mid- and forefoot, remain white with no statistically significant relationships evident between variability and speed. Figure 3.(a–p) RMA regression suggested positive linear relationships between m.s.e. (y axis) and Froude number in 11 out of 16 subjects, and CV (z axis) and Froude number in 15 out of 16 subjects. However, R2 and p-values (r2 > 0.75, p = <0.05) strongly support linear increases in variability with Froude in only four subjects when assessed by m.s.e. in four subjects, and in 11 subjects when assessed by CV (table 3). Froude number is (Fr = v2/g × LL), where v2 is speed squared, g is gravity (9.81 m s−2) and LL is each subject's leg length measured from the superior apex of the iliac crest to the where the heel meets the floor. Figure 4.(a–p) m.s.e. variation maps represent the distribution and magnitude of the combined mean m.s.e. in each pixel across the plantar surface of the foot at each speed trial in all subjects. Intra-subject spatial variability measured by the mean m.s.e. is highest and confined almost exclusively to the lateral and medial forefoot in all subjects; however, there is no consistent increasing or decreasing relationship between mean m.s.e. and speed. Figure 5.(a–p) CV variation maps represent the distribution and magnitude of the combined CV in each pixel across the plantar surface of the foot at each speed trial in all subjects. Intra-subject spatial variability measured by the CV is highest under the big toe and medial phalanges, as well as in the midfoot. There is no consistent increasing or decreasing relationship between mean CV and speed. Table 2.Regression statistics reveal a linear increase in m.s.e. with speed in only four subjects (subjects B, E, L, N). When assessed by CV, regression statistics reveal a linear increase in CV with speed in 10 subjects (subjects B, D, E, H, I, K, L, M, N, P).subjectcalculationR2p-valuesslopeinterceptAm.s.e.0.0101810.87175−0.439552.8989CV0.0843090.635560.358290.7358Bm.s.e.0.853920.0248251.24250.77694CV0.962160.0248251.5003−0.58675Cm.s.e.0.424120.233872.470.49312CV0.260870.379191.2834−0.17Dm.s.e.0.173870.484912.9502−0.10196CV0.739860.0614460.96520.05617Em.s.e.0.547970.152570.802831.0234CV0.731530.0646250.798050.51636Fm.s.e.0.0497470.718392.15862.1586CV0.276770.362490.736740.43294Gm.s.e.0.0516140.713242.77440.63995CV0.363760.281570.372310.89058Hm.s.e.0.107840.589523.4058−0.64398CV0.643910.102230.860140.10809Im.s.e.0.0817860.081786−1.33334.711CV0.736810.0626010.641070.21239Jm.s.e.0.332370.30894−1.33714.742CV0.200080.450081.0392−0.068518Km.s.e.0.40880.24542−1.54955.3533CV0.802210.0398170.710560.13506Lm.s.e.5.84 × 10−50.990270.712870.29741CV0.830650.0312330.785580.35856Mm.s.e.0.245190.396340.67866−0.29176CV0.910410.0117030.856540.067362Nm.s.e.0.748690.0581510.94132−0.086887CV0.925050.00891251.2525−0.53741Om.s.e.0.21920.426440.447260.65783CV0.256580.38381−1.2194−1.2194Pm.s.e.0.113620.57909−0.740772.5079CV0.763030.0529630.946360.94636 Table 3.Regression statistics reveal a linear increase in m.s.e. with Froude number in only four subjects (subjects B, E, M, N). When assessed by CV, regression statistics reveal a linear increase in CV with speed in 10 subjects (subjects B, D, E, F, H, I, K, L, M, N, P).subjectcalculationR2p-valuesslopeinterceptAm.s.e.0.00461520.91357−1.58682.5799CV0.128920.128921.29340.99583Bm.s.e.0.814870.0358974.05031.6787CV0.959110.00355394.89060.50204Cm.s.e.0.381290.267099.70092.2857CV0.252650.388095.04050.76138Dm.s.e.0.159010.5060810.3972.0391CV0.680140.0857473.40163.4016Em.s.e.0.590740.590742.71211.6061CV0.721490.0685452.69592.6959Fm.s.e.0.0522310.711575.41285.4128CV0.956260.237010.405580.96763Gm.s.e.0.121110.121110.566019.7704CV0.299580.299581.31121.1867Hm.s.e.0.0659150.06591512.2681.8277CV0.704060.0755893.09830.73232Im.s.e.0.0925190.618780.618783.759CV0.794260.0423632.45860.67764Jm.s.e.0.267840.26784−6.08783.9844CV0.238480.40394.73160.5203Km.s.e.0.360640.360640.28421−5.0511CV0.752010.0569342.31632.3163Lm.s.e.0.000387220.974952.00990.85545CV0.782170.0463522.72430.92868Mm.s.e.0.928680.432052.79450.12158CV0.90310.90313.36410.68899Nm.s.e.0.789120.789122.87450.6905CV0.69050.0044444.58780.37161Om.s.e.0.174440.484121.71530.98243CV0.291520.34758−4.67652.8734Pm.s.e.0.10530.5942−2.51541.9703CV0.744930.0595463.21360.77527