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Variation in human 3D trunk shape 
and its functional implications 
in hominin evolution
Markus Bastir1*, José María González Ruíz1, Javier Rueda2, Gonzalo Garrido López2, 
Marta Gómez‑Recio1, Benoit Beyer3, Alejandro F. San Juan2,4 & Enrique Navarro2,4
This study investigates the contribution of external trunk morphology and posture to running 
performance in an evolutionary framework. It has been proposed that the evolution from primitive 
to derived features of torso shape involved changes from a mediolaterally wider into a narrower, 
and antero‑posteriorly deeper into a shallower, more lightly built external trunk configuration, 
possibly in relation to habitat‑related changes in locomotor and running behaviour. In this context 
we produced experimental data to address the hypothesis that medio‑laterally narrow and antero‑
posteriorly shallow torso morphologies favour endurance running capacities. We used 3D geometric 
morphometrics to relate external 3D trunk shape of trained, young male volunteers (N = 27) to 
variation in running velocities during different workloads determined at 45–50%, 70% and 85% of 
heart rate reserve (HRR) and maximum velocity. Below 85% HRR no relationship existed between 
torso shape and running velocity. However, at 85% HRR and, more clearly, at maximum velocity, we 
found highly statistically significant relations between external torso shape and running performance. 
Among all trained subjects those with a relatively narrow, flat torso, a small thoracic kyphosis and 
a more pronounced lumbar lordosis achieved significantly higher running velocities. These results 
support the hypothesis that external trunk morphology relates to running performance. Low thoracic 
kyphosis with a flatter ribcage may affect positively respiratory biomechanics, while increased 
lordosis affects trunk posture and may be beneficial for lower limb biomechanics related to leg return. 
Assuming that running workload at 45–50% HRR occurs within aerobic metabolism, our results may 
imply that external torso shape is unrelated to the evolution of endurance running performance.
Evolutionary anatomical changes. 
The trunk consists of the ribcage, the spine and the pelvis. During 
human body shape evolution, each of these elements experienced specific morphological changes. For example, 
the ribcages of Homo erectus and Neandertals were not only wider at the level of the central and lower thorax, 
but also antero-posteriorly deeper than most modern human  populations1–4. Also the pelvis shows a systemic 
evolutionary trend towards reduction of its bi-iliac width, when comparing modern humans with H. erectus 
and members of the Neandertal  lineage5–8. Evolutionary changes in the spine of the genus Homo show changes 
in overall height, it’s position within the ribcage and possibly spine curvatures. Within Homo, the overall spine 
length has increased, as a consequence of larger body  size9. Greater dorsal orientation of the transverse processes 
in non-modern humans likely positioned the thoracic vertebral bodies more within the ribcage, producing a 
greater spine  invagination10,11. Also, in Neandertals a smaller lumbar lordosis (hypolordosis) is discussed and 
could be particularly relevant with respect to trunk morphology as it directly affects the position and orientation 
of the sacrum and, thus, the  pelvis12–14. The potential adaptive significance and functional implications of these 
features in hominin trunk evolution are not well understood and have been discussed in the context of thermo-
regulatory15,  digestive16,  respiratory3, and locomotor  functions17. Here, we focus on the latter two aspects.
Trunks with a narrow lower thorax and a narrow, tall waist have been associated with emerging endurance 
running capacities, possibly appearing with African H. erectus and together with elongated lower  limbs18. Yet, a 
recent reconstruction of the KNM-WT 15,000 African H. erectus ribcage seems more similar to Neandertals in 
OPEN
1Paleoanthropology Group, Museo Nacional de Ciencias Naturales, CSIC, J.G. Abascal 2, 28006 Madrid, 
Spain. 2Department of Health and Human Performance, Faculty of Physical Activity and Sports Sciences-INEF, 
Universidad Politécnica de Madrid, 28040 Madrid, Spain. 3Laboratory of Functional Anatomy (LAF), Faculty of 
Motor Skills Sciences, Université Libre de Bruxelles, Brussels, Belgium. 4These authors jointly supervised this work: 
Alejandro F. San Juan and Enrique Navarro. *email: mbastir@mncn.csic.es
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terms of width and depth than to modern human  populations3. Nevertheless, Neandertals are thought to show 
adaptations for sprinting based on the anatomy of their foot  skeleton19, and for power locomotion, as paleo-
ecological and genetic evidence indicates, which is interpreted in the context of ambush hunting in a forested 
 ecosystem20.
Thus, given the new evidence for greater similarities of trunk shape in primitive Homo and  Neandertals3, 
together with known differences in the lower limb anatomy,—i.e. longer limbs in H. erectus adapted to endurance 
 running17,18,21,22, and shorter limbs with specialized feet in Neandertals adapted to  sprinting19,20,23—it is inter-
esting to investigate the implications of variation in trunk morphology in the context of locomotor capacities.
Trunk anatomy and running capacities. 
The trunk contributes to locomotor performance and energet-
ics in two different ways: (1) the effect of trunk morphology on limb biomechanics, and (2) the effect of thorax 
morphology on breathing mechanics. Grossly speaking, sprinting and endurance running differ at energetic and 
locomotor (limb) biomechanics in the context of stride lengths, frequency and energetics. It has been shown that 
runners with relative longer lower limbs have lower locomotor  costs24. Effective sprinting requires greater stride 
 length25 and powerful lumbar muscles, specifically erector spinae and quadratus  lumborum26. Endurance run-
ning, nevertheless, does not require longer strides. Higher frequency is more important to running performance 
during long distances and time, especially in longer trails, where the loss of stride length typically appeared due 
to  fatigue27,28. Generally, a more upright trunk posture is observed among runners who perform efficiently in 
comparison with those less efficient, whose trunks were increasingly flexed during endurance  running29.
Besides a positive effect of overall trunk  muscularity26,30 on running performance, it has been shown that 
several other specific trunk morphological aspects relate to running performance, including the width of the 
 pelvis8,31, the trunk flexion  angle32, lumbar  lordosis33,34 and associated hip  flexion31, and thorax breathing 
 mechanics35,36.
Within modern humans, the relationship between the widths of the thorax and the pelvis are important 
parameters of human variability in form and  function37. The narrower pelvis relative to the wider thorax in males 
is associated with a gait pattern that differs biomechanically from that of females, who are characterized by a 
wider pelvis and narrower thorax  dimensions38. The width of the pelvis influences the biomechanics of the psoas 
major affecting its hip rotator and flexor  capacities31. Trunk flexion also affects significantly stride kinematics 
and kinetics. Although the factors of trunk flexion are unclear, higher trunk flexion angle correlates with shorter 
stride length, higher stride frequency, greater reaction forces and increased locomotion  costs32.
Lumbar lordosis varies considerably in human  populations12,39–41 and affects locomotor capacities. It has 
been shown that greater lordosis facilitates shock absorption, for example, when  running34, while weaker lor-
dosis produces a more forwards orientation of the pelvis, which is beneficial for leg return during  sprinting31. 
Weaker lordosis is also related to greater trunk muscle  strength33. Overall trunk muscularity (e.g. erector spinae, 
quadratus lumborum, psoas major, transverse abdominal, etc.…) has been correlated positively with sprinting 
 capacities26,30. Differences in the tonus of the erector spinae and quadratus lumborum muscles have been related 
to greater lumbar  lordosis42.
The contribution of thorax shape to trunk morphology is further interesting in the context of respiratory 
 biomechanics35,36. It has been suggested that morphological features of the rib joints are relevant for ventilatory 
capacity during  running43. These authors showed that H. erectus has similar rib joint morphologies as modern 
humans that differed from Australopithecus and chimpanzees. But also overall thorax morphology is important: 
antero-posteriorly flatter ribcages with more inferiorly declined ribs were suggested to show different thoraco-
diaphragmatic and abdominal muscle recruitment during ventilatory movement than antero-posteriorly deeper 
thoraces with more horizontally aligned  ribs44–46. Although pump- and bucket-handle patterns of rib motion 
seem more uniformly distributed along the ribs than originally  assumed47,48, variation in thorax-shape related 
breathing biomechanics indirectly affect the locomotor capacities due to energetic competition and demands 
between the locomotor and the respiratory  systems49,50. Thus, several studies have so far addressed the implica-
tion of specific elements of trunk morphology in isolation on locomotor performance. This study explores the 
relationship between entire 3D trunk shape and running performance based on virtual and geometric morpho-
metric  methods51,52. In the light of the functional anatomical evidence reviewed above, we address the hypothesis 
that trunks with an antero-posteriorly flat ribcage, a medio-laterally narrow pelvis and a lower lumbar lordosis 
are associated to a better running performance.
Materials and methods
Functional analyses, variables and experimental set up, ethics. 
Twenty-seven healthy trained 
young male students of the Degree in Sciences of Physical Activity and Sports (Table  1) were voluntarily 
recruited. Twelve of them were trained in endurance (ER) disciplines and fifteen were team sport players (non-
ER). The inclusion criteria were the following: (1) Age between 18 and 30 years; (2) volunteers athletes had to 
be either long distance runners or team sports players (e.g., rugby, soccer, basketball); (3) not having suffered a 
musculoskeletal injury one month prior to the date of the protocol (i.e., checked through a previous exclusion 
questionnaire). And exclusion criteria were: (1) Age younger than 18 years; (2) having consumed any narcotic 
and/or psychotropic agents or drugs during the test; (3) any cardiovascular, metabolic, neurologic, pulmonary, 
or orthopaedic disorder that could limit performance in the different tests. Informed consent was obtained by all 
volunteers. The study protocol adhered to the declaration of Helsinki and was approved by the Ethics Committee 
of the Technical University of Madrid (Spain).
All the participants performed a physiological (ramp) protocol on a treadmill (Telju JT4100-Liton -035, 
Toledo, Spain) in three different phases of exercise intensities: 45–50%, 70%, and 85% of the heart rate reserve 
(HRR). These three intensities correspond with the cardiorespiratory phase 1 [i.e., Light intensity, below the 
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ventilatory threshold (VT)], phase 2 [i.e., Moderate intensity, between the VT and the respiratory compensation 
threshold (RCT)], and phase 3 [i.e., High intensity, above the RCT)]27. The rate of perceived exertion (RPE) was 
introduced as a complement of the HRR to help the control of the adequate intensity in each of the three submaxi-
mal workloads (i.e., For a HRR of 45–50% the RPE should be 2–4/10, HRR of 70% the RPE 5–6/10, and for HRR 
85% the RPE ≥ 8/10). Before warm-up, rest heart rate was measured in sitting position until it was stable. After a 
general warm-up, the test started between 6 and 7 km  h−1 and 1% of slope to mimic effects of air  resistance53,54. 
Then, running velocity was increased by 0.5 km  h−1 every 30 s until the achievement of HRR ≥ 85%, RPE ≥ 8 and 
volitional exhaustion. The following variables were recorded at these instances: time, running velocity, and RPE. 
Heart rate (beats·min−1) was continuously monitored during the test using a telemeter (Polar Ceinture H10+; 
Polar Electro OY, Kempele, Finland). Changes in velocity during the different work load phases were analysed 
by repeated measures ANOVA carried out in  PAST55. Anthropometrical and running performance data were 
collected and summarized in Table 1 and Table 2.
3D shape data collection and geometric morphometric analyses. 
3D body surface data were man-
ually recorded by an Artec MHT 3D (www. artec 3d. com) surface scanner in standardized positions, standing 
upright on a turning table, with quiet breathing and the arms slightly raised over the head to leave the 360° of 
Table 1.  Descriptives of the sample showing age, body size, and weight.
Age (yr)
Stature (m)
Body weight (kg)
BMI
N
27
27
27
27
Min
18
1.62
53.50
19.97
Max
29
1.90
83.00
25.76
Mean
20.78
1.77
69.06
22.06
SD
2.53
0.07
7.20
1.34
Figure 1.  Frontal, lateral and posterior views of the 3D landmarks on the trunk surface. Red dots are 
fixed landmarks (Supplementary Table 1) and anatomically homologous between subjects, blue dots are 
curve semilandmarks, and green dots are surface semilandmarks. After resliding the semilandmarks are 
mathematically homologous among subjects.
Table 2.  Descriptive statistics of the running velocities at different experimental steps.
Vinitial (km/h)
V1 (km/h)
V2 (km/h)
V3 (km/h)
Vmax (km/h)
N
27
26
26
27
27
Min
6
6
8
12
12
Max
8
9
14
20
20
Mean
6.85
7.35
10.33
14.42
15.07
SD
0.43
0.75
1.35
2.09
1.81
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the trunk contour free for image caption. 160 landmarks and semilandmarks (Fig. 1) were digitized according to 
the template described in González-Ruiz et al.52 (Supplementary Table 1), and postprocessed following standard 
 methods56. Trunk landmark data were then analysed and visualized following standard methods of virtual, geo-
metric morphometric  analyses51. Specifically, generalized procrustes analysis (GPA) was carried out to obtain 
3D shape data and multivariate regression analyses were carried out on the 3D shape data on running veloc-
ity. In order to account for different influence of muscularity on torso shape in endurance and non-endurance 
athletes, we performed a pooled-within group regression. We also tested the hypotheses with a reduced torso 
landmark set (N = 142 lms), where those landmarks that covered the skin surface related to the latissimus dorsi 
and pectoralis major muscles were removed. Finally, we explored the data for a possible impact of stature and 
weight on running performance using GLM. We set the significance level for the regression analyses on p < 0.05. 
The analyses were carried out using MorphoJ  software57, PAST v3.2555, STATISTICA v.858, geomorph package 
for  R59,60 and Evan  toolkit61 following the workflows outlined in Bastir et al.51 (Table 2).
Results
Repeated-measures ANOVA (Table 3) shows that mean velocity increased significantly during incremental HRR 
phases (Fig. 2).
The regression analyses of torso shape on velocity phases indicated no significant relations during the first 
two stages (V1, V2) of workload. However, statistically significant relations were found between torso shape 
and velocity during phase 3 (V3) and maximum velocity (Vmax) (Table 4). Comparison of slopes in the ER and 
non-ER groups in the pooled within group regression models revealed no evidence for differences in the full 
torso shape data (P = 0.19; F = 1.833), nor in the non-muscular torso shape data (P = 0.18; F = 0.187) in relation 
Vmax. The GLM model revealed a significant influence of both, full and non-muscular torso shapes on running 
performance but no such effect of stature or weight (Table 5).
The associated 3D shapes (Fig. 2) show that the following morphological features of the trunk are positively 
associated with increased running performance: smaller antero-posterior diameter at the central-lower rib cage 
(flat thorax), narrower lower trunk (narrow pelvis), taller trunk, reduced thoracic kyphosis and more pronounced 
lumbar lordosis.
Discussion
Modern humans are characterized by a relatively flat and narrow ribcage and pelvis when compared to fossil 
representatives of the genus Homo that are characterised by more stocky, wider and antero-posteriorly deeper 
torso  configurations2–6,15,62,63. While more and more evidence seems to document this morphological trend, 
possible functional implications of reduced widths and depths of the trunk remain poorly understood. Because 
the trunk comprises elements of the respiratory and locomotor systems, the interaction of trunk shape with 
respiratory and locomotor performance is of specific interest.
In the present study, we address possible relations between torso shape and locomotor function in an experi-
mental setting relating 3D external trunk surface shape with running velocity at different levels of intensity. The 
results showed no relationship between trunk shape and running performance at lower levels of exercise (V1, 
V2) below the anaerobic (respiratory) threshold, and just above it, indicating no relations between external torso 
shape and endurance running speeds between 7 and 10 km/h. However, at higher intensities and velocities above 
the anaerobic (respiratory) threshold (V3; average 14.4 km/h) a statistical relation between torso shape and run-
ning speed emerged. According to our results, subjects with a flatter and slightly narrower thorax, lower thoracic 
kyphosis, more pronounced lumbar lordosis, and slightly narrower pelvis can achieve such higher velocities such 
as indicated by the higher variances of 3D trunk shape shown at V3 and maximum velocity. It has been suggested 
that an endurance running velocity of about (5  ms−1 = 18 km/h) can be sustained by many amateurs without 
special  training18, which is considerably faster than in our sample. At moderate intensity (V2), presumably within 
the aerobic metabolic domain, the average speed was about 10 km/h (Table 2). This may be related to the slight 
inclination of the treadmill (1%) during the incremental experiment (and the thereby simulated air resistance), 
but it could also reflect the fact that not all the volunteers were specialized endurance runners. Likewise, the 
average speed of 14 km/h at V3, which is likely already beyond the anaerobic threshold, is still lower than the 
published one and, again, could be related to the factors mentioned before. However, at and beyond this velocity, 
3D torso shape was statistically related to running capacity.
The most visible features related to higher running capacities were a low degree of thoracic kyphosis, with a 
flatter, slightly narrower central thorax and a greater degree of lumbar spine curvature with a relatively slightly 
narrower pelvis. Covariation in depths was more clearly recognisable than in widths (Fig. 2). While the thoracic 
part suggests interpretation within a respiratory biomechanical perspective, the lumbo-pelvic part of the torso 
Table 3.  ANOVA of velocities during the three different phases (V1, V2, V3).
Sum of sqrs
df
Mean square
F
p (same)
Between groups
1526.05
4
381.51
393.5
 < 0.001
Within groups
251.161
125
2.01
Error
96.954
100
0.96
Between subjects
154.207
25
6.17
Total
1777.21
129
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also requires consideration within functions of the locomotor system, although both are clearly related with each 
other. For example, the role of the posterior lumbar muscles is essential, as they act keeping an upright posture 
of the lower trunk during running and giving stability to the diaphragm and psoas major lumbar insertions. 
So, trunk extensors have the ability to reduce the kyphosis  angle64,65. Links between breathing biomechanics 
and lumbar stability have been found in Kang et al.66 who showed that spinal posture was improved by specific 
breathing exercises in a clinical context.
The combination of a reduced thoracic kyphosis and a flat ribcage, with anteriorly declined ribs, in which 
the anterior rib ends are more caudally located than the posterior rib ends, could point to the importance of 
ventilatory biomechanics in higher intensity running. Bellemare et al.44,45 suggested that declined ribs can be 
elevated more during inspiration than horizontally aligned ones accentuating potentially the costal contribu-
tion to thorax movement during lung ventilation. Also, anteriorly declined ribs may have better biomechanical 
leverage during forced expiration, which crucially increases the tidal volume during heavy exercise  breathing35. 
Because the declination of the ribs is morphologically related to a flatter rib cage configuration, the hypothesis 
that a flat thorax is positively related to running performance finds support. Physiologically, a less curved tho-
racic spine increases further the vertical space potentially available for lung expansion through enhancing of rib 
mobility. For example, negative consequences for lung ventilation due to kyphotic thoracic spine deformations, 
which compress thoracic space and affect rib biomechanics, have been  reported46,67.
The implication of lumbar lordosis for locomotor biomechanics consists of its effect on the forwards orienta-
tion of the anterior superior iliac spine, which is an advantageous position for efficient leg  return31. However, 
while these authors have not found a significant relation between lumbar lordosis angle and hip flexion capacity, 
Figure 2.  Torso shapes (160 lms) and thin-plate splines warped to the highest and lowest velocity at maximum 
intensity and running speed. (a) Non-muscular torso shape (142 lms) on maximum velocity. (b) Full torso shape 
(160 lms) on maximum velocity (c) Full torso shape warped to the configuration of lowest (left) and highest 
(right) maximum velocities. Upper panel left lateral view, lower panel frontal view. Note that flatter ribcages, 
narrower trunks with low thoracic kyphosis and more pronounced lumbar lordosis correlate significantly with 
higher velocities at maximum intensity. (Magnification factor from left to right: − 7.5; − 5; + 5, + 7.5, for better 
visualization).
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our results in Fig. 2 clearly show that more pronounced lumbar curvature, to which also the lower thoracic 
kyphosis contributes, produces forwards tilt of the pelvis.
Warrener et al.32 have found a significant reduction of length and an increment of frequency of strides associ-
ated with higher trunk flexion posture during running. This finding is supported by Castillo and  Liebermann34, 
who pointed out that higher lumbar lordosis (trunk extension) is linked with longer stride length in runners, a 
key factor in speed running as we have observed in our sample. Additionally, upright posture have been associ-
ated with better economy and running performance in the context mechanically interactions between trunk 
kinetics, reaction forces and spatiotemporal patterns of  strides29.
Table 4.  Multivariate regressions of full torso shape (160lms) and non-muscular torso shape (142 lms) on 
running performance at different workloads (V1, V2, V3 and Vmax). (Note that sample size is N = 27 for 
Vmax, but N = 26 for V1, V2 and V3). Significant values are in bold.
Df
SS
MS
R2
F
Z
p Value
160 lms
V1
1
0.003868
0.003868
0.04589
1.1543
0.54784
0.3
Residuals
24
0.080422
0.003351
0.95411
Total
25
0.08429
V2
1
0.00358
0.00358
0.04248
1.0646
0.30142
0.387
Residuals
24
0.08071
0.003363
0.95752
Total
25
0.08429
V3
1
0.005871
0.005871
0.06965
1.7968
1.8401
0.034
Residuals
24
0.078419
0.003267
0.93035
Total
25
0.08429
Vmax
1
0.007102
0.007102
0.08071
2.1948
2.4053
0.009
Residuals
25
0.08089
0.003236
0.91929
Total
26
0.087991
142 lms
V1
1
0.003644
0.003645
0.04369
1.0965
0.39524
0.359
Residuals
24
0.079767
0.003324
0.95631
Total
25
0.083412
V2
1
0.003291
0.003291
0.03945
0.9857
0.082949
0.458
Residuals
24
0.080121
0.003338
0.96055
Total
25
0.083412
V3
1
0.005547
0.005547
0.0665
1.7096
1.728
0.044
Residuals
24
0.077865
0.003244
0.9335
Total
25
0.083412
Vmax
1
0.006828
0.006828
0.07836
2.1256
2.2905
0.01
Residuals
25
0.080303
0.003212
0.92164
Total
26
0.08713
Table 5.  Generalized Linear Models assessing the effects of stature, weight, torso shape (160 lms, 142 lms) on 
running performance. Significant values are in bold.
SS
df
MS
F
p
160 lms
Intercept
7.93
1
7.93
5.38
0.030
Stature
0.51
1
0.51
0.35
0.562
Weight
0.88
1
0.88
0.60
0.447
Torso shape
46.85
1
46.85
31.79
0.000
Error
33.90
23
1.47
142 lms
Intercept
6.43
1.00
6.43
4.33
0.048
Stature
0.19
1.00
0.19
0.13
0.720
Weight
46.59
1.00
46.59
31.36
0.519
Torso shape
0.64
1.00
0.64
0.43
0.000
Error
34.16
23.00
1.49
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Therefore, the empirical evidence reported in the present study seems to indicate that trunk evolution as a 
whole may have brought about the appearance of some features that are more clearly related to long distance 
running, along with others that are more related to power locomotion with higher workloads. However, these 
features lead to a mosaic notion, which reflects a complex picture of potential adaptations to running economy.
In Neandertals, some adaptations to power locomotion were proposed on anatomical, genetic, and ecological 
 grounds19,20. Our results suggest that the relatively straight thoracic column along with their high level of trunk 
muscularity, possibly reflected by wide, deep thorax shape and associated high body mass estimates, would 
fit with the power locomotion  hypothesis2,68,69. On the other hand, their supposed hypo-lordosis would argue 
against such interpretation as the relatively uncurved reconstruction of the thoracic and lumbar spine in the 
Kebara 2  Neandertal13,69 would indicate reduced pelvic tilt and thus a reduced capacity of leg return, hip flexion 
and sprinting capacity. Yet, the most recent reconstruction of the La Chapelle aux Saints Neandertal suggests 
vertebral curvatures similar to modern  humans14 and this indicates that a better fossil documentation of lumbar 
spine anatomy in Neandertals is needed. Importantly, a recent study accounting for a wide range of population 
variability in modern humans, identified consistently and significantly more pronounced lordotic wedging in 
Neandertal L5 of Kebara 2, Shanidar 3, and La Chapelle aux  Saints41 together with a more hypo-lordotic wedg-
ing in upper lumbar vertebra. Accordingly, this could suggest a completely different position of the lumbar 
spine within the trunk, with yet unclear biomechanical implications. Therefore, further fossil reconstructions 
of Neandertal torso skeletons together with experimental testing are necessary.
In African H. erectus, as reconstructed on the remains of KNM-WT 15,000, the straight  thoracic3 and curved 
lumbar spine  morphology70 would be more in line with effective power-locomotion. This, together with greater 
torso width and depth would be also compatible with higher muscularity and body  mass3,15,63,71,72. However, 
clearly, the elongated limbs favour an interpretation of long-distance locomotion and, possibly,  running17,21. 
Altogether, the present evidence and reviews suggest that our interpretations relate to a great extent on the reli-
ability of the fossil body reconstructions.
However, it is important to bear in mind the limitations of our experimental evidence in the evolution-
ary context of endurance running. Obviously, the fossil record does not contain information about soft tissue 
anatomy, while the present data was exclusively collected on the external surface of the torso and so the relations 
between skeletal and soft tissue anatomy are unknown. Yet, bony features are considered. The curvature of the 
spine is assessed by the tips of the spinous processes which are variable in terms of sagittal orientations and thus 
do not directly inform about the curvature as assessable on the basis of the vertebral bodies. Also, the ribcage 
anatomy is only indirectly reflected by the skin surface landmarks and closer to skeletal thorax shape only at 
the central and lower parts of the rib cage. These data can thus only give a general idea about thorax shape. The 
pelvic landmarks are clearer in this respect as the iliac spines can be identified without problems. However, the 
reduced landmark set, which excluded shape information related to the latissimus dorsi and major pectoralis 
muscles may be less influenced by muscularity, and the fact that the results of the full and the reduced data are 
similar suggests little soft tissue effects on the results.
Further limitations are related to the proper running experiment. Endurance running in the evolutionary 
context appeared in the context of specific climatic conditions that were not considered in the present experi-
ment. Also, actual endurance running is defined as running at intermediate velocities and aerobic conditions 
for longer time than considered in our experiment, where we only tested for potential relations between veloc-
ity and aerobic running conditions during the early stages of the incremental exercise. In this perspective, our 
data are only informative about shape-function relation during higher intensity running. Future studies should 
relate torso shape to running performance data on velocity and distance during longer trails and in hot weather 
conditions. Such analysis will provide further insight into the important relationships between torso shape, body 
shape and locomotor performance relevant for human evolution.
Received: 22 December 2021; Accepted: 22 June 2022
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Acknowledgements
We thank the volunteers for participating in this study. Funding: Grant PID2020-115854GB-I00 to MB is funded 
by MCIN/AEI/10.13039/501100011033 of the Spanish Ministry of Science and Innovation and the European 
Union. We thank Prof. Mitteroecker and one anonymous reviewer for their helpful comments.
Author contributions
M.B. designed the associated research project, collected 3D surface data, analysed the geometric morphometrics 
data, wrote the main manuscript and pepared the Figures. J.M.G.R. collected and postprocessed the 3D-landmark 
data, preprared Figures and wrote parts of the paper. M.G.R programmed code and analysed additional data. 
M.B., B.B., A.S.J. and E.N worked on the development of the experimental procedures. M.B., J.R., G.G.L., A.S.J. 
and E.N. carried out the experiments and A.S.J and E.N supervised all steps of the experiment at the laboratory. 
All authors reviewed the manuscript.
Competing interests 
The authors declare no competing interests.
Additional information
Supplementary Information The online version contains supplementary material available at https:// doi. org/ 
10. 1038/ s41598- 022- 15344-x.
Correspondence and requests for materials should be addressed to M.B.
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© The Author(s) 2022

Variation in human 3D trunk shape and its functional implications in hominin evolution.
Bastir, Markus,González Ruíz, José María,Rueda, Javier,Garrido López, Gonzalo,Gómez-Recio, Marta,Beyer, Benoit,San Juan, Alejandro F,Navarro, Enrique