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Citation: Sekulovi´c, V.;
Jezdimirovi´c-Stojanovi´c, T.; Andri´c,
N.; Elizondo-Donado, A.; Martin, D.;
Miki´c, M.; Stojanovi´c, M.D.M. Effects
of In-Season Velocity-Based vs.
Traditional Resistance Training in
Elite Youth Male Soccer Players. Appl.
Sci. 2024,14, 9192. https://doi.org/
10.3390/app14209192
Academic Editor: Isaac López-Laval
Received: 25 August 2024
Revised: 3 October 2024
Accepted: 5 October 2024
Published: 10 October 2024
Copyright: © 2024 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
applied
sciences
Article
Effects of In-Season Velocity-Based vs. Traditional Resistance
Training in Elite Youth Male Soccer Players
Veselin Sekulovi´c 1, Tatjana Jezdimirovi´c-Stojanovi´c 2, Nikola Andri´c 1,2 , Andoni Elizondo-Donado 3,
Diego Martin 4, Mladen Miki´c 1and Marko D. M. Stojanovi´c 1,2 ,*
1Faculty of Sport and Physical Education, University of Novi Sad, 21000 Novi Sad, Serbia;
veselinsekulovic@gmail.com (V.S.); nikola.trenaznaekspertiza18@gmail.com (N.A.);
mmmikac@gmail.com (M.M.)
2Training Expertise, 21000 Novi Sad, Serbia; tatjanaj.ns@gmail.com
3Faculty of Education and Sport, University of the Basque Country, UPV/EHU, 01007 Vitoria-Gasteiz, Spain;
2c.andonie@gmail.com
4Department of Physical Activity and Health, Osasuna Mugimendua Kontrola S.L. Mugikon, 48450 Bilbao,
Spain; diegomartin9640@gmail.com
*Correspondence: marko.ns.stojanovic@gmail.com
Abstract: The objectives of this study were to compare the effects of two in-season velocity loss
training methods (VBT) on performance outcomes and to evaluate the effects of velocity-based
training compared to traditional resistance training (TRT) on performance outcomes in young elite
soccer players. VBT utilized the same relative load but varied in the extent of velocity loss during the
set: 15% (VL15%) and 30% (VL30%). Thirty-four players were recruited and randomly distributed
into three groups: the VL15% group (n = 12; age = 18.50
±
0.67 years; stature = 183.41
±
4.25 cm; body
mass = 75.08
±
5.57 kg), the VL30% group (n = 11; age = 17.91
±
0.60 years; stature =
181.21 ±6.56 cm
,
body mass = 73.58
±
6.22 kg), and the traditional strength training group TRT (n = 11; age =
18.14 ±0.74
years; stature = 182.17
±
5.52 cm; body mass = 74.86
±
6.68 kg). Alongside regular soccer sessions
and matches, the groups underwent a four-week (2 sesions per week) resistance training intervention
with back squats involved. Changes in leg strength (SQ1RM), 20 m sprint time (SPR 20 m), counter-
movement jump height (CMJ), reactive strength index (RSI), and change of direction (COD) from
before and after were evaluated using a 3
×
2 ANOVA. While no significant interaction was found
for SQ1RM and SPR20, all of the groups showed significant pre to post improvements. Significant
interactions were observed for CMJ (F = 38.24, p= 0.000), RSI (F = 8.33; p= 0.001), and change of
direction agility test (COD) (F = 3.64; p= 0.038), with a post hoc analysis showing differences between
the VL15 (6.0%) and TRT (1.7%) groups (p= 0.034); VL15 (12.2%) and VL30 (3.2%) groups (p= 0.004);
VL15 and TRT (0.4%) (p= 0.018); VL15 (2.4%) and VL30 (1.5%) (p= 0.049); and between the VL15
and TRT (0.4%) groups (p= 0.015). Four weeks of VL15% training during the season induced similar
strength increases to VL30% and TRT, superior improvements in RSI and COD compared to VL30%,
and superior improvements in CMJ, RSI, and COD tests compared to TRT. Thus, incorporating the
VL15% training method may be recommended to improve power-related performance metrics in
elite young soccer players.
Keywords: velocity-based training; strength training; vertical jump; change of direction ability
1. Introduction
Resistance training (RT) is well established as an integral component of soccer training
and as a powerful training stimulus for soccer players’ performance improvement [
1
]. It
has been consistently reported that actions critical to winning in soccer are predominantly
executed at a high intensity, encompassing sprints, changes of direction, jumps, tackles,
and other movement patterns that demand increased lower body strength and power [
2
].
RT specific outcomes are largely influenced by several training variables, with relative
Appl. Sci. 2024,14, 9192. https://doi.org/10.3390/app14209192 https://www.mdpi.com/journal/applsci
Appl. Sci. 2024,14, 9192 2 of 12
intensity and volume considered to be determining factors of resulting neurophysiological
adaptations [
3
]. Furthermore, optimizing the load and volume of time spent on resistance
training is a crucial concern during the season, considering a wide range of fitness attributes
and skills that must be consistently incorporated in the training process [
4
]. As a result,
there is an ongoing demand for identifying and integrating effective yet efficient strength
training methods into soccer training [
5
]. Various resistance training modalities aimed
at enhancing strength and power have been introduced over the years, with traditional
resistance training considered as a bencmark for prescribing training loads [
6
]. These
traditional resistance training methods are prescribed based on individuals’ 1RM (one
repetition maximum), not considering athletes’ daily fluctuations, and thus may lead to
loading them inappropriately while decreasing training efficacy [
7
]. In this context, several
resistance training methods, with the umbrella term, “autoregulative resistance training”,
were developed recently to enable real-time adjustment of the training intensity according
to an individual’s daily fluctuations in performance and training-induced fatigue [
8
]. The
recent availability of kinematic measuring devices and the established correlation between
relative load and barbell velocity—when the load is lifted at maximum intended velocity
in a non-fatigued state [
9
,
10
]—have driven the adoption of barbell velocity as a metric
for intensity; a practice referred to as velocity-based training. An increasing amount of
evidence suggests that VBT methods to load and volume prescription can induce significant
neuromuscular adaptations and physical performance improvements [
11
] in addition, the
term covers variety of approaches with velocity loss thresholds [
12
] found to be superior to
others in terms of strength and power performance outcomes [
13
]. The training load for
each session is defined by the velocity of the fastest repetition, with repetitions continued
until velocity falls below a predetermined threshold, indicating the percentage velocity loss
(%VL) for the set.
Numerous studies conducted over the past few decades have examined various per-
centages of velocity loss (%VL). Some research [
14
–
16
] indicates that a low %VL (
5–15%
)
leads to comparable or greater improvements in strength, sprint time, and jumping ability
than a higher %VL (greater than 20%), while not all studies have reached the same conclu-
sion [
17
,
18
]. Interestingly, two recently published reviews comparing the effectiveness of
velocity-based training (VBT) and traditional strength training presented conflicting results.
One review [
19
] indicated that lower velocity loss positively impacts strength, jumping,
and sprinting performance compared to traditional resistance training methods, while the
other found no evidence of any differences between VBT and traditional strength training
in these outcomes [20]. More studies about the topic are required.
Despite the current importance of resistance training prescription, only a few studies
using the velocity loss approach in soccer players have been published. In a 6-week (2 se-
sions per week) study with professional players, Pareja-Blanco et al. [
21
] found that group
training with a volume load of 15% (15% VL) resulted in significantly greater improvements
in strength (estimated one-rep maximum) and power (vertical jump) compared to group
training with 30% VL. However, no between-group differences were detected in terms of
sprinting and endurance gains. Similarly, Rojas-Jaramilo et al. [
22
] proved 10% velocity
loss training to be superior to 30% velocity loss training in improving strength, sprint, and
vertical jump in non-trained young soccer players. Finally, in a sample of strength-naïve
young female soccer players with three training sessions per week for 12 weeks during
the preseason period, velocity-based training was proven to be superior compared to
traditional strength training in countermovement jump and squat power but not maximal
squat strength [23].
It is evident that a notable gap remains in the understanding of VBT application
within soccer cohorts. Moreover, the lack of research focused on young elite soccer players
precludes insights into how effective well-established training modalities can be for highly
trained youth athletes. Understanding how different approaches impact strength and
power adaptations specifically in this demographic could provide valuable insights to
strength and conditioning coaches aiming to maximize performance in competitive settings.
Appl. Sci. 2024,14, 9192 3 of 12
The objectives of this research are two-fold: 1. To compare the effects of two in-season
velocity loss training methods on performance outcomes, and: 2. To evaluate the effects
of velocity-based training in comparison to traditional resistance training on performance
outcomes in young elite soccer players. According to a recent review [
19
], we hypothesized
that low velocity-based training (15% VL) would lead to greater improvements in power-
related fitness attributes.
2. Materials and Methods
2.1. Participants
Thirty-four elite youth soccer players volunteered to take part in this study and
were randomly divided (lottery method) into 3 groups: velocity-based training group
with 15% velocity loss alowed in each set—VL15 (n = 12; age = 18.50
±
0.67 years;
stature =
183.41 ±4.25 cm
; body mass = 75.08
±
5.57 kg), velocity-based training group
with 30% velocity loss allowed in each set—VL30 (n = 11; age = 17.91
±
0.60 years;
stature = 181.21
±
6.56 cm, body mass = 73.58
±
6.22 kg), and traditional resistance
training group—TRT (n = 11; age = 18.14
±
0.74 years; stature = 182.17
±
5.52 cm; body
mass = 74.86
±
6.68 kg), which took part in a traditional resistance training program. Mea-
surements were taken using an SECA measuring rod along with an SECA model scale (Seca
GmbH, Hamburg, Germany) with 1 mm and 0.1 kg precision for height and body mass,
respectively. Height was determined with the participant’s head held in the horizontal
Frankfort plane position. The technical error of measurement (TEM) for height and body
mass was under 0.02%.
All players were of an elite youth level, playing for two teams competing in the Serbia
youth quality league, finishing second and third during the season when the investigation
took place. The inclusion criteria for all players were as folows: (1) had at least 4 years
of soccer training experience; (2) were free from lower limb injuries or illnesses in the 3
months leading up to the study; and (3) had a minimum of two years of resistance training
experience from their time in previous age group squads. A typical in-season microcycle for
the teams consisted of 5 soccer sessions (90 min per session), 2 strength and conditioning
training sessions, and 1 game. The objectives, testing procedures, and responsibilities
during this study were thoroughly communicated to all the participants. Each individual
had the option to withdraw from the research at any point. All of the players were free
from injury through the study duration, and all finished with over 90% attendance. During
the study intervention, there were no reported musculoskeletal injuries or other medical
issues that could interfere with the training, and none of the players used medications or
dietary supplements. The procedures adhered to the Declaration of Helsinki, and the study
protocol was reviewed and approved by the ethics committee of the University of Novi
Sad, Serbia (Ref. No. 33-01-07/2021-3). All of the participants and/or their parents/legal
guardians received verbal information about the study during one meeting and were
provided with a detailed written document explaining this study. All of the participants or
their parents or legal guardians voluntarily provided written consent for their participation.
2.2. Study Design
A longitudinal and experimental study employing a between-subjects design was
conducted to evaluate the effects of load manipulation based on velocity loss or as a per-
centage of one-repetition maximum (1RM) within a 4-week resistance training program.
This study took place during the latter half of the season (March–April 2021/2022). One
week prior to the initial testing, the subjects became acquainted with all of the test pro-
cedures. After testing, the players from the VL15 and VL30 groups performed 3 to 4
sets of 3 to 4 repetitions of the squat exercise with varying weights to become familiar
with the training protocol. Three days before the program commenced, both the VL15
and VL30 groups participated in an additional familiarization training session. Both the
initial and final testing took place across two sessions. Prior to all tests, a standardized
warm up was introduced, consisting of a light jogging session, dynamic stretching, and
Appl. Sci. 2024,14, 9192 4 of 12
lower limb activation exercises. On day one, the subjects’ anthropometric characteristics
were recorded before a 20 m sprint, and 1RM squat tests were conducted, respectively.
Two days later, the subjects performed jumping tests, COD tests, and finished with an
incremental load–velocity squat test, respectively. Supervised strength training sessions for
the groups took place in the mornings at 9:00 a.m. at their respective clubs, equipped with
all necessary materials, including GymAware, bars, plates, and elastic bands. Each session
was led by three experienced strength and conditioning coaches with a strong background
in velocity-based training (VBT) to ensure high-quality training. The sessions were held
on Tuesdays and Thursdays, occurring 75–90 min before the regular soccer practice. Final
testing was conducted no less than three days after the intervention period, mirroring the
initial testing in terms of timing, order, protocols, and examiners. The participants were
strongly advised to refrain from any strenuous activities for 24 h prior to testing.
2.3. Measurements
One repetition maximum—1RMSQ
The participants underwent one-repetition maximum (1RM) testing for the free-weight
squat following guidelines established by the National Strength and Conditioning Associa-
tion [
24
]. The process started with a standardized warm-up including dynamic stretching
and preparatory exercises. This was followed by a series of warm-up sets: five repetitions
at approximately 50% of their estimated 1RM, three repetitions at around 70% of 1RM, and
two repetitions at about 80% of 1RM. Afterward, the participants attempted their 1RM with
progressively heavier weights. A research team member monitored their squat depth to
ensure that the participants reached a parallel position (thighs parallel to the floor). The
participants were permitted up to five attempts, with their highest successful lift recorded
as their one-rep max (1RM).
Individualized load–velocity relationships
A linear encoder was utilized to assess the mean velocity (MV) during free-weight
back squats (GymAware (GYM), Kinetic Performance Technologies, Canberra, Australia).
The participants carried out the half-squat exercise starting from an upright stance. They
descended at a self-regulated average speed of approximately 0.50–0.70 m
·
s
−1
until the
thighs were parallel with the floor. Then, they immediately reversed the movement to
ascend back to the upright position at their maximum intended velocity. Before the main
exercise, the participants completed a standardized warm-up like that performed in the
one-repetition maximum (1RM) test. They then executed three repetitions at 30% of their
baseline 1RM, followed by three at 60%, two at 80%, and one at 90%. Earlier studies verified
that GYM provides excellent reliability of MV measurements within the range of 40–90%
of 1RM [
24
]. The participants received verbal encouragement and velocity feedback to
achieve maximal concentric velocity on each repetition. A three-minute rest period was
allowed between each load. Only the quickest repetition achieved for each absolute load
was retained for future analysis. Individualized load–velocity profiles were developed by
plotting mean velocities (MVs) against their corresponding loads and applying a line of
best fit. The MVs for 60% and 80% of the one-rep max (1RM) were subsequently used to
modify the training loads in the velocity-based training (VBT) groups.
Drop jump—RSI index test
In the DJ test, thevparticipants descended from a 30 cm box using their preferred leg,
landed on a contact mat with both feet, and then jumped as high as possible. They were
instructed to maximize their jump height while minimizing the time spent in contact with
the mat during the transition from landing to jumping. Each participant completed the test
three times, taking a 30 s rest between jumps, and the highest result was noted for further
analysis. The reactive strength index was determined by calculating the flight time/contact
time (in seconds) ratio. The highest score was used for analysis.
The Countermovement Jump Test (CMJ) was conducted following the Bosco pro-
tocol [
25
] using a contact platform (Just Jump, Probotics, USA). The participants were
directed to place their hands on their hips and maintain an upright position as they dy-
Appl. Sci. 2024,14, 9192 5 of 12
namically lowered themselves to a depth of their choosing before jumping upward with
maximal effort and landing with their knees fully extended. Each participant was allowed
three attempts, with a passive rest period of 45 s between repetitions. The highest jump
performance recorded from these attempts was used for subsequent analysis.
20 m Sprint Test (SPR20)
The participants underwent a 20 m sprint test, which was timed using light gates
(Witty; Microgate, Bolzano, Italy). After a designated warm-up that featured two submaxi-
mal efforts, each subject completed two trials. They began from a crouched position with
their front foot positioned 0.5 m before the first timing gate, and they started voluntarily to
eliminate reaction time. Throughout the test, the subjects received verbal encouragement to
exert maximum effort. A two-minute passive recovery period was implemented between
trials. The best performance from the trials was selected for subsequent statistical analysis.
In the 505 change of direction tests, light gates were positioned 5 m from a specified
turning point. The players began from a starting position 10 m away from the timing gates
(15 m from the turning point). Each subject started with their front foot 0.5 m before the
timing gate. They were instructed to accelerate through the timing gates as quickly as
possible, decelerate at the 15 m mark, and then re-accelerate to return through the timing
gates with maximum intention. Two trials were completed with 120 s of passive rest, with
the better result used for further analysis.
2.4. Training Interventions
The participants took part in two resistance training sessions to familiarize themselves
with the training method, thereby optimizing their training adaptations. All three groups
completed a total of 4 weeks of individually supervised strength training, consisting of 2
sessions per week (on Tuesdays and Thursdays), which amounted to 8 training sessions
overall. All of the groups also had their usual weekly competitive microcycle, consisting of
a recovery day, four soccer field practices, game day, and a day off (Table 1).
Table 1. Microcycle.
Mon Tue Wed Thu Fri Sat Sun
AM
RT
Soccer field
practice
Soccer field
practice
RT
Soccer field
practice
Soccer field
practice
PM Off Off Off Off Off Match day Recovery
AM—morning; PM—afternoon; RT—resistance training.
During the 4-week intervention, the resistance training loads (expressed as a per-
centage of 1RM), the number of sets, and the rest periods between sets were consistently
maintained across all groups. The TRT group performed back squats at 80% and 60% of
their baseline 1RM during the first and second sessions of the week, respectively. These
loads were chosen because they are commonly used in strength training programs, effec-
tively target specific physical qualities along the strength–velocity continuum, and yield
reliable velocity data [
24
]. For the VL15 and VL30 groups, relative loads were established
based on the individual squat load–velocity relationship, as recent research has shown a
strong correlation between %1RM and mean velocity (MV). Consequently, a target MV
for the first repetition of the first exercise set in each session was determined as an esti-
mate of %1RM. The targeted MV for the VL15% group was 0.729
±
0.075 m/s at 80% of
1RM and 0.861
±
0.099 m/s at 60% of 1RM. For the VL30% group, the targeted MPV was
0.724 ±0.048 m/s at 80% of 1RM and 0.831 ±0.06 m/s at 60% of 1RM.
The absolute load (in kg) was adjusted for each participant to match the desired
velocity, maintaining a tolerance of
±
0.06 m
·
s
−1
in relation to the targeted %1RM for each
session. If the maximum movement velocity (MV) during a set of 5 repetitions deviated
by
±
0.06 m/s from the target velocity, the barbell load was modified by
±
5% of 1RM for
Appl. Sci. 2024,14, 9192 6 of 12
the next set. Alongside the back squat as the main compound movement, supplementary
exercises were incorporated into the training program (Table 2).
Table 2. Descriptive characteristics of the base training program.
Exercise Sets ×Reps Load
Training session 1
BB back squat 3 ×6
PBT 80% 1RM,
VBT: load that aligns with a 80%
of 1RM movement velocity.
Bench press 3 ×6 Body weight
Deadlift 3 ×6 2 RIR
BB bent-over row 3 ×6 1 RIR
OHP 3 ×6
Lunge † BM+
Training session 2
BB back squat 3 ×8
PBT 60% 1RM,
VBT: load that aligns with 60%
of 1RM movement velocity
Bench press 3 ×10 2 RIR
Deadlift 3 ×10 2 RIR
BB bent-over row 3 ×10 1 RIR
OHP 3 ×10 2 RIR
Hip thrust 3 ×10 2 RIR
RM—one repetition maximum; BB—barbell; BM—body mass; OHP—overhead press; RIR—repetitions in reserve;
† lunge load calculated [16]: 0.6 (6RM squat [kg; 0.52] + 14.82 kg).
To maintain consistency across the groups in these exercises, the sets and repetitions
were standardized, with the load calculated using specific equations related to body mass
or by using a repetitions-in-reserve method (refer to Table 2). All of the participants were
given strong verbal encouragement throughout their repetitions to inspire them to give
their best effort.
2.5. Statistical Analysis
All of the tested variables were expressed as means
±
standard deviations (SDs).
The assumption of normality was evaluated using the Shapiro–Wilk test, while Levene’s
test was utilized to assess homoscedasticity. Baseline differences between the groups
were determined through a univariate analysis of variance (ANOVA), considering the
factor group (VL15, VL30, and TRT). The differences between measurements taken before
and after the intervention were analyzed using paired samples t-tests for each group
individually, and between-group comparisons under the influence of the experimental
treatment were assessed using a two-way ANOVA (3x2). The level of significance was
established as p
≤
0.05. A post hoc Bonferroni test following the ANOVAs was performed
to determine the significance of the interactions between factors. The mean difference effect
size was determined using Cohen’s d, which was calculated by subtracting the means
and dividing the outcome by the pooled standard deviation. The Cohen’s d values were
interpreted according to Hopkins et al. [
26
] (small, 0.2; medium, 0.5; large, 0.8; very large,
1.3). Data analysis was executed using the SPSS statistical software package, version 20
(Chicago, IL, USA).
3. Results
No significant differences among the groups were found in the pretest for any of
the variables analyzed. Additionally, no significant interaction was identified for SQ1RM
(F = 1.96; p= 0.158) and SPR20 (F = 0.542; p= 0.578) (Table 3). Pre vs. post comparisons
showed significant improvements for SQ1RM in all groups, with 8,4% (moderate effect
size), 10.2% (moderate effect size), and 10.9% (large effect size) for the VL15, VL30, and TRT
groups, respectively. In addition, for SPR20m, significant differences from preintervention
to postintervention were seen for all the groups, although with a small improvement
Appl. Sci. 2024,14, 9192 7 of 12
percentage (1.6% for VL15 and VL30 and 1.2% for TRT) and trivial effect size for all
the groups.
Table 3. Pre–post and between-group differences between selected variables with % improvement
and Cohen’s effect size (d).
VL15 VL30 TRT
IN FIN % dIN FIN % dIN FIN % dp
SQ1RM
106.83
±
12.23 115.83
±
12.50
*8.4
0.72 101.09
±
9.89 111.45
±
9.07
*
10.2 1.09 105.00
±
7.51
116.45 ±7.64
*
10.9 1.49
0.000
CMJ 56.63 ±7.94 60.04 ±8.28
*6.0
0.42
50.51 ±4.72 53.65 ±4.97
*6.2
0.66
50.98 ±4.77 51.85 ±4.71 *
1.7 0.18
0.000 ‡
RSI 2.45 ±0.21 2.75 ±0.26 *
12.24 1.42
2.18 ±0.23 2.25 ±0.29 3.2
0.26
2.27 ±0.33 2.28 ±0.29
0.4 0.03
0.001 †‡
SPR20m
3.00 ±0.76 2.95 ±0.89 * 1.6
0.06
3.07 ±0.43 3.02 ±0.33 * 1.6
0.11
3.09 ±0.50 3.05 ±0.44 *
1.2 0.08
0.587
COD 2.20 ±0.09 2.10 ±0.06 * 2.4
1.11
2.27 ±0.10 2.22 ±0.10 * 1.5
0.50
2.29 ±0.09 2.24 ±0.11
0.6 0.55
0.038 †‡
SQ1RM—1RM squat test; CMJ—countermovement jump test; RSI—reactive strength index test SPR20m—20 m
sprint test; 505 test—change of direction test; IN—initial tests result ±standard deviation; FIN—final test result;
%—percent improvement; p—level of statistical significance; * statistically significant difference pre vs. post
p< 0.05
;
†
—statistically significant difference between VL15 and VL30 group;
‡
—statistically significant difference
between VL15 and TRT group.
A significant interaction was observed for the Countermovement Jump (CMJ) test
(F = 38.24, p= 0.000), with the post hoc analysis revealing differences between the VL15
and TRT groups (p= 0.034). When comparing the initial and final measurements, the VL15
group demonstrated a 6.0% improvement (moderate effect size), while the VL30 group
showed a 6.2% improvement (moderate effect size). In contrast, the TRT group had a
smaller improvement of 1.7% (trivial effect size). For the Reactive Strength Index (RSI), a
significant interaction was noted (F = 8.33; p= 0.001), with the post hoc analysis revealing
differences between the VL15 and VL30 groups (p= 0.004) as well as between the VL15 and
TRT groups (p= 0.018). The VL15 and VL30 groups achieved improvements of 12.2% (large
effect size) and 3.2% (small effect size), respectively, while the TRT group saw a minimal
improvement of 0.4% (trivial effect size). The COD test also showed a significant interaction
(F = 3.64; p= 0.038). The post hoc analysis indicated significant differences between the
VL15 and VL30 groups (p= 0.049) and between the VL15 and TRT groups (p= 0.015), but
no significant difference was found between the VL30 and TRT groups (p= 0.980). In terms
of percentage improvements from pre- to post-testing, the VL15 group improved by 2.4%
(moderate effect size), the VL30 group improved by 1.5% (moderate effect size), and the
TRT group improved by 0.6% (trivial effect size).
4. Discussion
Research indicates that velocity-based training can effectively improve various fitness
attributes in athletes. However, there is a scarcity of studies focused on its effectiveness in
soccer. Thus, this investigation aimed to compare the impacts of two in-season velocity loss
methods (VL15 and VL30) with traditional strength training (TRT) on leg strength, change
of direction ability, jumping, and sprinting performance in elite youth soccer players. The
present study results confirmed that all the groups significantly increased their strength
level, with no significant differences in strength-enhancing capacity between the groups.
VL15 was proved to be superior to both VL30 and TRT in developing the reactive strength
index (RSI) and COD test. In addition, all three groups significantly increased in their
countermovement jump pre vs. post (p< 0.05), only VL15 significantly improved in RSI,
and both VL 15 and VL30 significantly improved in their COD performance. In accordance
with the initial hypothesis, it seems that adding two sessions a week for four weeks of
velocity-based training with a relative load of 60–80% and velocity loss threshold of 15%
appears to be a more robust strategy than VL30 or traditional strength training for lower
body strength, jumping, and change of direction performance enhancement during the
competitive period in elite youth soccer players. Ultimately, neither training method was
shown to be effective in improving 20 m sprint performance.
A growing body of studies have recently emerged evaluating the impacts of different
%VLs on the set on performance outcomes in athletic populations, with the presented
Appl. Sci. 2024,14, 9192 8 of 12
data generally in line with this study’s findings. In an 8-week study involving 16 training
sessions conducted by Pareja-Blanco et al. [
15
], it was found that velocity-based training
(VBT) with a 20% velocity loss produced squat strength gains similar to those achieved
with a 40% velocity loss (18% and 13.4%, respectively). Additionally, the 20% velocity loss
group demonstrated significantly greater improvements in counter-movement jump (CMJ)
performance, showing an increase of 9.5% compared to just 3.5% in the 40% velocity loss
group (p< 0.05) among resistance-trained young athletes. The outcomes of the 8 weeks of
Rodriguez-Rosell et al.’s study [
27
] demonstrate that VL10% training conducted twice a
week resulted in larger percentage increases in Countermovement Jump (CMJ) performance
(9.2% compared to 5.4%) and sprint performance (
−
1.5% versus 0.4%) compared to VL30%
in resistance-trained young males. Three velocity-based groups (VL10%, VL30%, and
VL45%) underwent eight weeks of velocity-based training (VBT) with consistent training
parameters: a load of 55–70% of one-repetition maximum (1RM), a training frequency
of two sessions per week with three sets per session, and a four-minute recovery period
between sets. All of the groups demonstrated significant improvements in muscle strength
(VL10%: 6.4–58.6%; VL30%: 4.5–66.2%; VL45%: 1.8–52.1%; p< 0.05–0.001). Notably, the
VL10% group experienced a significantly greater improvement in counter-movement jump
(CMJ) performance (11.9%), as well as a larger percentage change in sprint performance
compared to the other two groups (VL10%:
−
2.4%; VL30%:
−
1.8%; VL45%:
−
0.5%).
Finally, two recently published reviews dealing with the effects of VBT on the performance
outcomes of elite athletes [
28
] and trained individuals [
29
] suggest that VBT may effectively
improve maximum leg strength, countermovement jump, and sprint ability. Furthermore,
it appears that implementing smaller velocity losses (up to 20%) promotes more beneficial
neuromuscular adaptations, decreases neuromuscular fatigue, and ensures a higher quality
of performance with a significantly lower total volume of training. Overall, the previously
mentioned study supports this study’s findings that low velocity loss training leads to
superior power-related performance while yielding similar strength outcomes compared to
high velocity loss training (30%) in athletes.
VBT appears to be an effective method for enhancing performance attributes in well-
trained individuals. This is widely supported by various studies that compare the effects
of VBT with traditional resistance training on performance outcomes. In a six-week (two
sessions/week) study of trained men by Dorelli et al. [
16
], the VBT group achieved similar
improvements in back squats (9% vs. 8%) and a significantly better jump height (5% vs. 1%)
when compared with a TRT approach, despite a significant 9% reduction in the total training
volume. Additionally, a comparison of six weeks of velocity-based training (VBT) versus
traditional resistance training (TRT), conducted with resistance-trained individuals [
30
],
demonstrated more favorable training outcomes for the VBT group in jump height (effect
size = 1.81), sprint performance (effect size = 1.27–1.35), and change of direction (effect
size = 0.67–0.97). However, it remained unclear if either training method was superior
for enhancing maximal strength (effect size =
−
0.57). The observed training effects were
greater than those reported in the present study, which could be attributed to the longer
study duration (6 weeks compared to 4 weeks) as well as the higher volume of lighter loads,
faster training repetitions, and consequently, more pronounced adaptations in the velocity
aspect of the force–velocity curve and high-speed actions such as the countermovement
jump, sprint, and change of direction [
14
]. Furthermore, the increases in maximal strength
observed for both groups in this study were nearly identical to the present study’s findings
for the VL30% and TRT groups (10.2%, ES = 1.09 and 10.9%, ES = 1.49, respectively). These
results were also slightly higher than those reported by Dorrell et al. (~9%, ES = 0.59 vs.
~8%, ES = 0.44 for VBT and TRT, respectively) and our VL15% group (8.4%, ES = 0.72). The
six-week study comprised two weekly sessions dedicated to free weight squats, with a
progressively increasing load that ranged from 65% to 90% of the 1RM, aimed to evaluate
the impact of velocity-based resistance training compared to traditional resistance training
on the athletic performance of college female basketball players [
31
]. Despite similar
strength gains (22.3%, ES = 1.39 vs. 19.4, ES = 3.09), velocity-based training was proved to
Appl. Sci. 2024,14, 9192 9 of 12
produce more favorable improvements in CMJ (7.3%, ES = 0.53), RSI (23.9%, ES = 0.85) and
the COD test (4.6%, ES = 0.87). In addition, no group-by-time interaction and no significant
improvements were found for sprint performance, altogether corroborating the present
study’s findings.
Interestingly, only a few studies have compared the effects of VBT with different
%VL and/or traditional resistance training on performance within a population of soccer
players [
21
–
23
]. Two previous studies, Pareja-Blanco et al. (2017) and Rojas-Jaramillo et al.
(2024), compared resistance training programs in male soccer players using similar %VL in
the set (10 vs. 30% and 15% vs. 30%, respectively). Although the range of relative loads
used was lower (50–70% 1RM and 45–60% 1RM), the results obtained were generally in line
with the present study’s findings: groups the lower velocity loss in both studies showed
larger improvements in countermovement jump (5.3%; ES: 0.40 and 8.0%, ES: 0.51) and
similar in 1RM strength (5.3%; ES: 0.45 and 22.2, ES: 1.65). In addition, while sprint time
showed no significant improvements pre vs. post in the Parejo-Blanco study (0.4%: ES 0.10),
being practically identical to the present study’s findings, Rojas-Jamarillo’s study reported
significant and large sprint time pre vs. post improvements (11.3%, ES: 1.85). This difference
could likely be attributed to both the younger age of this study’s participants compared to
both ours and Pareja-Blanco’s study, as well as the resistance training history (resistance
training naïve cohort). Finally, to the best of our knowledge, only one study compared
the effects of velocity-based training and traditional strength training. Ortega et al. [
23
]
examined the effects of VBT (20% velocity drop threshold with load equivalent to 65% of
1RM) vs. TRT (load equivalent to 80% of 1RM) on 30 sprint time, countermovement jump,
lower body maximum strength, and maximal squat power. The presented data indicate
that the VBT group, with a 42% lower volume of training, produced significant increases
in maximal strength (p< 0.000), squat power (p< 0.000), 30m sprint time (p< 0.000), and
countermovement jump (p< 0.001), with squat power and CMJ being meaningfully better
than the results of the TRT group (p< 0.008). Together, the aforementioned data support
the effectiveness of velocity-based training in enhancing strength and power performance
attributes in well-trained youth soccer players. However, it is essential to exercise caution
regarding the threshold load required to achieve the desired improvements. Clearly, further
research on this topic is needed.
It is noteworthy that we did not find significant effects of either velocity-based training
or traditional resistance training on the 20 m sprint time among our participants. This aligns
with the findings of Pareja-Blanco et al. (2017), who reported no change in 20 m sprint
times following lower load velocity-based training in professional soccer players. It can be
speculated that the obtained results may be partly due to the training status of the current
study’s participants (well-trained), as research has shown that trained adolescents tend to
improve less in sprint outcomes with resistance training than their untrained peers [
32
].
Furthermore, the training and testing specificity may influence outcomes, as the upward
force vector applied during this study training sessions is likely crucial for inducing specific
functional adaptations [33].
The present study results demonstrated significant changes in the performance param-
eters when utilizing velocity loss methods, with smaller velocity losses usually eliciting
greater neuromuscular adaptations compared to larger velocity losses. Although this study
does not address them, it is worth briefly hypothesizing the mechanisms that could explain
the observed improvements in the performance outcomes. Clearly, reducing velocity losses
allows for higher-quality repetitions, leading to greater speeds attained during the exercise
session.
Parejo-Blanco et al. [
18
] explored the effects of applying velocity losses of 20% and 40%
in young males on performance enhancements, changes in muscle fiber characteristics, and
cross-sectional area. Their findings revealed that the group experiencing a high velocity
loss of 40% exhibited a significant decrease in type IIX fibers, which could adversely affect
strength and power development as well as lengthen recovery times [
34
]. In addition,
Rodríguez-Rosell et al. [
14
] demonstrated that their low velocity loss group (VL10%)
Appl. Sci. 2024,14, 9192 10 of 12
experienced significant improvements in strength, jumping, and sprinting performance,
which were accompanied by increased neural activation of the agonist muscles involved in
the exercises. In contrast, neural activation remained unchanged for the VL30% and VL45%
groups. Collectively, these findings suggest that establishing a low velocity loss limit (5–
15%) during each exercise set leads to both effective and efficient training stimuli, promoting
significant neuromuscular adaptations while requiring fewer repetitions and inducing
lower levels of fatigue (mechanical and physiological stress) compared to training volumes
associated with higher velocity loss thresholds. This could be of particular importance
during soccer season, when the general objective of resistance training is to induce long-
term benefits on performance outcomes while maintaining peak performance during
subsequent field soccer practice. Indeed, resistance training with heavy loads and near
failure repetitions per set has been shown to induce greater short-term deterioration in jump,
sprint, and change of direction compared to lower repetitions or %VL in the set [
35
,
36
].
These physiological differences reinforce the present study’s findings and highlight the
advantageous use of velocity-based training to optimize strength and power adaptations
in elite youth soccer players.
Several limitations of this study should be noted. The participant sample is limited
to players from Serbia, and we do not know whether athletes from other countries have
the same characteristics. The training load was manipulated solely for the back squat;
however, this approach is consistent with previous velocity-based training (VBT) studies.
Adjusting the load for other lower-body exercises in the training routine, such as the deadlift,
forward lunge, and hip thrust, using velocity thresholds was not deemed appropriate, as
maximizing concentric velocity was not the primary training objective for these movements.
Additionally, we did not monitor the load used during regular soccer practice sessions
conducted among all three groups with their respective coaches, which could have impacted
the training adaptations. Lastly, this study only lasted four weeks, highlighting the need
for comparative investigations using strength modalities over longer durations.
5. Conclusions
It seems that adding two sessions a week for four weeks of velocity-based training
with a relative load of 60–80% and velocity loss threshold of 15% appears to be a more
robust strategy than VL30% or traditional strength training for jumping and change of
direction performance enhancement during the competitive period in elite youth soccer
players. In addition, all three resistance training modalities were comparably effective in
maximal strength gains. Strength and conditioning specialists may consider implementing
low velocity loss training modalities during the competitive season in elite youth soccer
players to achieve substantial improvements in the mentioned performance outcomes.
Author Contributions: M.D.M.S. and V.S. served as the study coordinators. M.D.M.S. and V.S.
conceived of and designed the experiments. T.J.-S., N.A. and M.M. assisted in data collection. A.E.-D.
and D.M. analyzed the data. T.J.-S., N.A. and M.M. assisted in the analysis and manuscript review.
M.D.M.S., V.S., and N.A. wrote the draft. T.J.-S., D.M., M.M., N.A. and A.E.-D. assisted in the statistics,
discussion analysis, and manuscript preparation. All authors have read and agreed to the published
version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: The institutional review board of the University of Novi Sad
approved of this research (Ref. No. 33-01-07/2021-3).
Informed Consent Statement: Informed consent was obtained from all subjects involved in this study.
Data Availability Statement: The data are available from the author upon reasonable request.
Acknowledgments: This article is dedicated to Z. Djindjic (1953–2003).
Conflicts of Interest: Author Tatjana Jezdimirovi´c-Stojanovi´c is co-owner the company Training
Expertise. The remaining authors declare that the research was conducted in the absence of any
commercial or financial relationships that could be construed as a potential conflict of interest.
Appl. Sci. 2024,14, 9192 11 of 12
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