Simple foot strike angle calculation from three-dimensional kinematics: A methodological comparison

Figures & data

Table 1. Current 2D and 3D two-marker methods for estimating foot strike angle are defined and cited below.

Reference	Analysis Type		Proximal	Prox. Abbrev.	Distal	Dist. Abbrev.
Lieberman et al. (2010)	2D	video	Posterior aspect of the calcaneus	HEEL	Lateral aspect of the fifth MTP joint	MET5
Giandolini et al. (2014)	2D	video	Lateral aspect of the calcaneus	HEELLAT	Lateral aspect of the fifth MTP joint	MET5
Lieberman et al. (2015)	2D	video	Lateral aspect of the calcaneus	HEELLAT	Lateral aspect of the fifth MTP joint	MET5
Nunns et al. (2013)	2D	motion capture	Posterior aspect of the calcaneus	HEEL	Lateral aspect of the fifth MTP joint	MET5
Holowka et al. (2021)	3D	motion capture	Posterior aspect of the calcaneus	HEEL	Superior aspect of the fifth MTP joint	METSUP5
Altman & Davis (2012)	3D	motion capture	Posterior aspect of the calcaneus	HEEL	Superior aspect of the second MTP joint	TOE
Mann et al. (2014)	3D	motion capture	Posterior aspect of the calcaneus	HEEL	Virtual midpoint of the fifth MTP joint and the first MTP joint	METMID1,5
Kelly et al. (2018)*	3D	motion capture	Medial aspect of the medial malleolus	ANKMED	Medial aspect of the first MTP joint	MET1

* = in relation to body segment (not ground surface); MTP = metatarsophalangeal.

Table 2. Participant characteristics are presented as mean ± standard deviation.

	n	Age (yr)	Mass (kg)	Height (m)	Running shoe drop (mm)	Velocity (m ∙ s^−1)	Natural FSP (n)
							FF	MF	RF
Total	12	31.1 ± 7.8	70.7 ± 12.2	1.75 ± 0.10	9.5 ± 1.8	3.43 ± 0.59	1	2	9
Male	7	30.4 ± 6.7	77.6 ± 9.2	1.80 ± 0.07	10.0 ± 0.0	3.71 ± 0.59	1	1	5
Female	5	32.0 ± 9.8	61.0 ± 8.9	1.67 ± 0.08	9.0 ± 2.6	3.08 ± 0.34	0	1	4

FSP = foot strike pattern; FF = forefoot, MF = midfoot, RF = rearfoot

Figure 1. The marker placements on the left foot can be seen from a lateral (a) and medial (b) views.

Figure 2. The calculation of the angle of the vector that spans from Marker 1 to Marker 2 is defined in geometric context. X, Y, Z = 3D spatial coordinates of Markers 1 & 2. Marker 1 = proximal marker (i.e., HEEL); Marker 2 = distal marker (i.e., TOE or MET₅); θ = foot strike angle.

Table 3. The mean and standard deviation of the foot strike angle determined from three kinematic methods are presented below. V3D-REF = reference method using a visual 3D virtual foot; HEEL-MET₅ = two markers (placed on the heel and laterally on the 5^th metatarsal); HEEL-TOE = two markers (placed on the heel and superiorly on the 2^nd metatarsal).

Strike Style	n	Method
		V3D-REF (°)	HEEL-MET5 (°)	HEEL-TOE (°)
FF	172	−3.3 ± 8.1	−7.0 ± 6.1	−3.9 ± 8.0
MF	289	3.1 ± 6.2	−1.0 ± 4.8	3.0 ± 6.1
RF	726	14.9 ± 6.8	9.9 ± 6.1	14.7 ± 6.8

FF = forefoot, MF = midfoot, RF = rearfoot

Table 4. The mean differences, correlation coefficients, and least squares regression statistics are presented comparing both two-marker methods (HEEL-MET₅ and HEEL-TOE) for determining foot strike angle against a reference method (V3D-REF).

Test	Statistic	V3D-REF vs. HEEL-MET5	V3D-REF vs. HEEL-TOE
reANOVA	Mean Difference (°) [CI]	4.28 [4.07, 4.91]*	0.28 [0.19, 0.36]*
Pearson r	Correlation Coefficient	0.968*	0.994*
Least Squares Regression	Constant (°) [CI]	1.091 [1.075, 1.107]	0.992 [0.987, 0.997]
	Intercept (°) [CI]	4.146 [3.988, 4.310]	0.276 [0.208, 0.344]
	Total bias ± SD (°)	−4.58 ± 2.61	−0.20 ± 1.05
	TEE (°) [CI]	2.49 [3.29, 2.59]	1.05 [1.02, 1.09]

* p < 0.001; CI = 95% confidence interval; SD = standard deviation

Figure 3. The regression line (solid) and line of equivalence (dashed) are presented above for both method comparisons: A = V3D-REF vs. HEEL-MET₅, B = V3D-REF vs. HEEL-TOE. The foot strike pattern distribution is colour coded: FF = forefoot (green), MF = midfoot (red), RF = rearfoot (blue) .

Figure 4. The mean ± SD of the measured foot angle are plotted against the ground contact phase (%) in the first and third rows of graphs (V3D-REF = grey scale; HEEL-MET₅ and HEEL-TOE are presented in colour). Positive angles are indicative of dorsiflexion while negative angles of plantarflexion. Each colour corresponds to a foot strike pattern (FF = forefoot (green), MF = midfoot (red), and RF = rearfoot (blue)). Each foot angle graph has a corresponding Statistical Parametric Mapping (SPM) analysis located in the row below it. The critical thresholds (t*) of the SPM analyses are plotted in dashed lines and reported numerically. Shaded areas above the upper t* and below the lower t* are clusters where significant differences exist between the angles measured by the two methodologies (α = 0.025). SPM{t} = t-score continuum across stance phase.

Lieberman, D. E., Venkadesan, M., Werbel, W. A., Daoud, A. I., D’Andrea, S., Davis, I. S., Mang’Eni, R. O., & Pitsiladis, Y. (2010, January). Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature, 463(7280), 531–535. https://doi.org/10.1038/nature08723

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Lieberman, D. E., Castillo, E. R., Otarola-Castillo, E., Sang, M. K., Sigei, T. K., Ojiambo, R., Okutoyi, P., & Pitsiladis, Y. (2015, July 8). Variation in foot strike patterns among habitually barefoot and shod runners in Kenya. PLOS ONE Internet]. Retrieved September 8, 2021, from 10 (7), e0131354. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0131354

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Kelly, L. A., Farris, D. J., Lichtwark, G. A., & Cresswell, A. G. (2018, January). The influence of foot-strike technique on the neuromechanical function of the foot. Medicine & Science in Sports & Exercise, 50(1), 98–108. https://doi.org/10.1249/MSS.0000000000001420

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