Variation of Kinematic and Dynamic Parameters with the

Use of Minimalist Shoes in the Entry Phase of the Hammer Throw

Gian Mario Castaldi

, Sebastiano Conci

, Andrea Amodio

, Filippo Goi

, Silvia Camboni

Alessandro Di Gregorio

and Valentina Camomilla

Foro Italico University, Rome, Italy

Star Horse Riding Care, Rome, Italy

Vibram Spa, Italy

Washburn University, Topeka, U.S.A.

Keywords: Hammer Throw, Biomechanics, Minimalist Footwear, Motion Capture, Ground Reaction Force.

Abstract: This study investigates the biomechanical implications of footwear choice on the start phase of the hammer

throw, aiming to determine whether minimalist footwear can be integrated into training without negatively

affecting technical execution. A cohort of six trained hammer throwers performed the initial three rotations

(start phase) under two different footwear conditions: standard World Athletics-approved throwing shoes and

minimalist Fivefingers shoes by Vibram. Participants were divided between two motion capture laboratories

for geographical reasons while ensuring consistent methodological application across environments. The

objective was to assess whether the minimalist footwear—known to enhance activation of intrinsic foot

musculature—alters key technical elements of the throwing motion. Analysis was structured around five

biomechanically relevant instants within the entry phase, before the start of the turns, enabling comparison

across footwear conditions of five parameters relative to the hammer head and the right foot motion, obtained

using stereophotogrammetry (tangential hammer velocity, right joint movements and ground reaction forces.

Preliminary results aim to determine whether the use of minimalist footwear brings an advantage to the

throwers in the entry phase of throwing and whether it can be a useful tool for use in training.

INTRODUCTION

In hammer throwing, the entry phase represents one

of the most critical phases for efficient execution.

This phase occurs between the preliminary swings

selection potentially influential on performance. As

throw, the efficient transfer of force begins at

highlighted in biomechanical analyses of hammer the

ground level, where the foot plays a pivotal role in

stabilizing and initiating rotational momentum

(Dapena, 1986; Murofushi et al., 2005), and the

rotational turns of the thrower-hammer system

(Judge, 2000). During this phase, accelerating the

hammer requires significant contribution from both

https://orcid.org/0009-0000-4299-9957

https://orcid.org/0009-0009-4932-2047

https://orcid.org/0000-0002-7452-120X

intrinsic and extrinsic foot muscles, making footwear

may represent a possible alternative.

The choice of footwear for competition and

training may therefore impact technique and Current

World Athletics-endorsed throwing shoes have a

rigid, heavy structure, while minimalist footwear may

represent a possible alternative.

Minimalist footwear - characterized by minimal

cushioning, flexible soles, and wide toe boxes - aims

to replicate barefoot conditions with the potential to

enhance natural foot movement, proprioception, and

intrinsic muscle activation. Some research suggests

that minimalist shoes may increase plantar flexor and

intrinsic foot muscle strength compared to

conventional footwear (Ridge et al., 2018), although

Castaldi, G. M., Conci, S., Amodio, A., Goi, F., Camboni, S., Di Gregorio, A. and Camomilla, V.

Variation of Kinematic and Dynamic Parameters with the Use of Minimalist Shoes in the Entry Phase of the Hammer Throw.

DOI: 10.5220/0013739000003988

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 13th International Conference on Sport Sciences Research and Technology Support (icSPORTS 2025), pages 217-222

ISBN: 978-989-758-771-9; ISSN: 2184-3201

217

such evidence is context-dependent and not specific

to hammer throw.

While direct evidence regarding the use of

minimalist shoes in hammer throwing is limited, the

biomechanical demands of the entry phase suggest

that such footwear could offer potential benefits. This

phase requires precise footwork, rapid weight shifts,

and finely tuned postural control—all of which

depend heavily on foot muscle strength and sensory

input. Despite its biomechanical complexity and

critical role in initiating effective hammer

acceleration, the entry phase remains

underrepresented in the literature (Rozhkov et al.,

2020). A recent review has further highlighted the

scarcity of studies on this specific phase, underlining

the need for more focused investigations (Castaldi et

al., 2022).

It has been hypothesized that stronger foot

muscles might improve stability and force

transmission, while enhanced sensory feedback could

help throwers in maintaining posture and control

during the critical transition from preliminary swings

to rotational turns. However, these potential benefits

have not yet been verified in hammer throwers.

Indeed, posture and proprioceptive control in the

early phases of the throw are essential for maintaining

optimal hammer trajectory and velocity (Brice et al.,

2008; Bartonietz, 2008).

Additionally, by promoting more natural foot

placement, minimalist shoes could influence

elements such as the left foot's heel pivot and right

foot's toe positioning during entry. Whether this

translates into improved movement efficiency

remains to be determined.

Therefore, this study analyses whether two

different footwear types can modify technique or

efficiency during the hammer throw entry phase.

METHODS

2.1 Participants

This research was approved by the University of

Rome “Foro Italico” local institution Review Board

(CAR 194/2024). Six hammer throwers (three men

and three women, height 1.78 ± 0.08 m; body mass

80.7 ± 13.5 kg; age 21.0 ± 4.9 years) included in the

top ten positions of the Italian U20, U23, or senior

category rankings participated in the study. Data

acquisition took place at the University of Rome

“Foro Italico” laboratory (Rome) and at the Vibram

Connection Lab (Milan).

2.2 Protocol

Two types of entry phases were analysed, without

performing the throwing phase. The first (3gr)

involved no pre-start of the hammer before the

preliminary rotations, no displacement of the right

foot at the end of the preliminaries, and an initial

rotation on the heel of the left foot. The second (4gr)

included a hammer pre-start before the preliminary

swings, with the displacement of the right foot at the

end of the preliminary swings and an initial rotation

on the left forefoot. Each type of start was performed

twice with both World Athletics approved throwing

footwear (WA) and Vibram Fivefingers KSO Evo

minimalist footwear (MS). MS is a very light and

flexible minimalist shoe, while WA is a heavy and

rigid shoe (fig. 1). Throwing with MS therefore

allows more efficient use of the muscles of the foot

and promotes the thrower's sensitivity. In contrast,

with WA the sensitivity and use of the intrinsic foot

muscles are less, but due to the greater stiffness of the

shoe, reaction forces from the ground are transferred

more and more efficiently to the thrower's body.

Figure 1: Marker protocol and shoes.

2.3 Data Acquisition

Two motion-capture system were used to measure

movement kinematics: in lab1, an 8-cameras

SMART-DX 4000 (BTS Sp.a.; @250 frame/s); in

lab2, a 4-Vero and 5-Bonita infrared cameras

(VICON®, Oxford Metrics, Oxford, UK; @200

frame/s). Two floor-embedded force plates were used

to assess ground reaction force - GRF (lab1: BTS

S.p.a 40x60cm., Milano, IT, lab2: Bertec Corp.,

Columbus OH USA, 40x40cm, both @1000 Hz).

Data were processed using Vicon Nexus 2.10 (Vicon,

Oxford, UK). Athletes were equipped with the

Clinical Gait Model (CGM, v.2.5) protocol, while the

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Figure 2: Key instants of the entry phase: the beginning of the active phase after the last preliminary turn Instant 1), the

descending phase of the hammer on the right side of the thrower (Instant 2), the passage of the hammer in front of the thrower's

right foot (Instant 3), the reaching of the low point of the hammer's path (Instant 4), and the end of the entry phase with the

landing of the right foot from the ground (Instant 5).

hammer carried 4 markers: one at the beginning of the

wire connected to the handle, and three applied on the

maximal circumference at 120 deg respective

separation (fig. 1). To minimize inter-laboratory

differences, the same experimenter performed the

anatomical calibration and sensors\markers

placement in both laboratories.

2.4 Data Analysis

Raw marker trajectories and analogue signals were

imported using ezc3d and organized into a nested

structure grouped by subject, footwear condition

("WA" for World Athletics shoe, "MS" for minimal

shoe), trial type (3gr, with rotation in the entry on the

heel of the left foot and usually used for a three turn

throw technique, or 4gr, with rotation on forefoot and

usually used for a three turn throw technique), and

repetition.

2.5 Key Instants

In the research five critical moments were defined to

analyze motion (fig. 2): the point where HAMMER is

furthest to the left of the thrower on the frontal plane

(Instant 1, I1), the point at which LFMH, RFMH and

HAMMER are on the same line (Instant 2, I2), the

point at which LFMH, RFMH and HAMMER form a

right angle on RFMH (Instant 3, I3), the lowest point

of HAMMER relative to the ground (Instant 4, I4)

and the point where the right foot loses contact with

the ground (Instant 5, I5). The five key instants (I1–

I5) were determined for each repetition using a

combination of velocity thresholds and temporal

heuristics using data from force platforms, right and

left feet heel (RHEE, LHEE) and first metatarsal

heads (RFMH, LFMH) and the hammer marker

cluster, used to compute the implement’s centroid.

2.6 Key Parameters

For every repetition, the CGM2.5 model was used to

determine the plantar-dorsiflexion of both ankles

(LAnkleAngles and RAnkleAngles) and the athlete’s

centre of mass (COM). The hammer centroid

tangential velocity was computed relative to subject

COM, along the X, Y, and Z axes. Ground reaction

forces under the right (Rfoot) and left foot (Lfoot)

were represented in a body frame perspective along

the anteroposterior (AP), mediolateral (ML), and

vertical (VERT) directions (i.e. force plate axes were

assigned to anteroposterior or medio-lateral

according to the feet orientation), and computed at the

5 key instants.

2.7 Statistical Analysis

Statistical analyses were conducted using Python

libraries (statsmodels, scipy, and pandas). For each

dependent variable, normality of residuals was tested

using the Shapiro-Wilk test and the homogeneity of

variances was evaluated using Levene’s test.

Descriptive statistics were computed using mean and

standard deviation, for variables meeting both

assumptions, and median and interquartile ranges

(IQR) for non-normally distributed ones.

Prior to inferential analysis, extreme outliers were

removed using a z-score threshold of ±3, and trials

with missing data were excluded on a per- variable

basis. Variables meeting Shapiro-Wilk and Levene

assumptions were analysed using a two-way

ANOVA, with shoe (WA vs MS) and trial (3gr vs

4gr) as fixed factors (table 1). If assumptions were

violated, the non-parametric Scheirer–Ray–Hare test

was applied. When main effects or interactions were

statistically significant (p < 0.05), pairwise post-hoc

comparisons were conducted using the Tukey HSD

test to identify specific condition differences.

Variation of Kinematic and Dynamic Parameters with the Use of Minimalist Shoes in the Entry Phase of the Hammer Throw

219

3 RESULTS

The analysis of ground reaction forces revealed

significant differences for footwear type only for the

left foot in the vertical direction at instants I1 and I4,

AP direction at I3 and ML direction at I4 (fig. 3).

More significant differences were found across

tasks in GRF, always for the left foot, at the instant I1

along the AP and vertical direction; at instant I2 along

the ML and vertical ones; at instant I4 and I5 along the

AP direction. In all cases 4gr task entailed greater

forces (fig. 3).

Figure 3: a. anterior-posterior (ap), b. medio-lateral, and c. vertical components of ground reaction force (GRF, normalized

to body weight, BW) during contact of the right foot (Rfoot) and left foot (Lfoot) at the five moments of support (I1–I5). Four

types of footwear are reported: Minimal Shoe (MS) and World Athletics approved footwear (WA), each tested on three (3gr)

and four turns (4gr). The bars represent the median and interquartile range, while dots show the outlier. The symbols ‘*’

highlight statistically significant differences between conditions (p < 0.05).

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Table 1: Statistically significant differences.

variable Test p shoe p trial descriptive

Lfoot_I2_ml

[N/BW]

Two-way

ANOVA

0.17

0.01

mean=-0.18

sd=0.51

Lfoot_I4_ml

[N/BW]

Two-way

ANOVA

0.01 0.32

mean=-0.24

sd=0.47

Lfoot_I1_ap

[N/BW]

Two-way

ANOVA

0.20

0.00

mean=-0.17

sd=0.51

Lfoot_I3_ap

[N/BW]

Two-way

ANOVA

0.01 0.34

mean=-0.24

sd=0.47

Lfoot_I4_ap

[N/BW]

Two-way

ANOVA

0.67

0.00

mean=-0.41

sd=0.44

Lfoot_I5_ap

[N/BW]

Two-way

ANOVA

0.63

0.00

mean=-0.40

sd=0.44

Lfoot_I1_vert

[N/BW]

Two-way

ANOVA

0.02 0.02

mean=-0.43

sd=0.20

Lfoot_I2_vert

[N/BW]

Scheirer-

Ray-Hare

0.58

0.02

median= -0.23

IQR=0.68

Lfoot_I4_vert

[N/BW]

Scheirer-

Ray-Hare

0.04 0.15

median= -0.37

IQR=0.47

Lank_I5

[deg]

Scheirer-

Ray-Hare

0.82 0.24

median=3.8

IQR=4.8

Rank_I1

[deg]

Two-way

ANOVA

0.04 0.41

mean=14.1

sd=15.6

Rank_I2

[deg]

Two-way

ANOVA

0.03 0.50

mean=16.1

sd=14.8

Rank_I3

[deg]

Two-way

ANOVA

0.05 0.70

mean=14.1

sd=14.8

Rank_I4

[deg]

Scheirer-

Ray-Hare

0.04 0.40

mean=14.5

sd=17.5

Rank_I5

[deg]

Two-way

ANOVA

0.04 0.15

mean=14.7

sd=14.3

vel_I3

[m/s]

Scheirer-

Ray-Hare

0.57

0.05

median=44.1

IQR=15.6

The analysis of the velocity modulus revealed

differences in velocities only at instant I3, which were

higher during the 4gr task.

The right ankle presented significantly wider

ranges of planta-flexion when using the MS shoes at

all instants of time, irrespective to the test condition.

DISCUSSION

This pilot study compared the impact of using two

different footwear types on the hammer throw entry

phase technique and efficiency. Results on ankle

angles, force exchanged with the ground, and hammer

tangential velocity suggest that the effects of footwear

are context-dependent and should not be generalized

without considering specific surfaces, movements,

and individual factors.

As no throwing phase was performed,

performance outcomes such as release velocity or

distance were not available in the present analysis.

Therefore, no speculation can be made regarding the

potential effects of these differences on overall

performance. The limited sample size did not allow

neither to observe general traits, nor to cluster athletes

across different behaviour and certainly requires

expansion.

Some athletes presented a tendency worth further

investigation. In some of them the use of MS, being a

more flexible footwear than WA, promotes more

excursion of the right ankle joint and induces a start

in which the vertical components of force are

predominant over the horizontal ones. With WA

footwear, the thrower compensates with more

horizontal expressions of force, especially in the

second part of the entry phase with the left foot

(Instants 3, 4 and 5). Considering that from instant 4

the hammer is in the ascending phase of the orbit, it

is important that the footwear allows for an active

action on the hammer in the most effective way

possible, and therefore a greater efficiency in the

development of horizontal components of the force

could better support the tangential velocity of the

hammer in this phase of the entry. In this phase of the

throw, the rotary components of the throw are

predominant over the translatory ones.

This study suggests that the contribution to speed

generation in the entry phase may be greater with

WA, in accordance with the evolution of footwear

used in competition, which in the 1980s was light and

flexible and over the years has been replaced by

increasingly rigid models, that enhance the return of

energy from the ground. The importance of footwear

in enabling ground reaction force transmission and

rotational efficiency has been discussed in relation to

foot-ground interaction dynamics (Murofushi et al.,

2007; Wang et al., 2014). Conversely, it is likely that

the greater stresses to which the intrinsic and extrinsic

musculature of the foot is subjected make the use of

MS in training more proficient in the quest to improve

the muscular capabilities of throwers.

Future research could investigate differences in

muscle recruitment using a larger number of subjects

and using EMG. They could also investigate with

longitudinal studies the potential effects of

habituation on muscle recruitment using different

footwear.

CONCLUSION

Preliminary analyses of the hammer throw entry

phase with two footwear types show that minimalist

shoes can promote greater vertical force components,

while World Athletics shoes favour horizontal forces.

These effects appear context-dependent and

preliminary due to the limited sample and the absence

of performance outcomes. Overall, the results suggest

Variation of Kinematic and Dynamic Parameters with the Use of Minimalist Shoes in the Entry Phase of the Hammer Throw

221

complementary roles for the two footwear types, with

rigid shoes suited to competition and minimalist

shoes potentially useful in training.

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