Ítalo Santiago Alves Viana*

italo.viana@ufv.br

Marcela Siqueira Benjamim*

marcela.benjamim@ufv.br

Leonardo Silveira Goulart Silva*

leonardo.goulart@ufv.br

Jorman Alexis Londoño Bombo*

jorman.bombo@ufv.br

Daniela Alejandra Melo Lopez*

daniela.lopez@ufv.br

Alice Ribeiro Cutis Vaz**

alice.r.vaz@ufv.br

Alice Ferreira Mathias**

alice.mathias@ufv.br

Antonio Carlos Marques Pires**

antonio.c.pires@ufv.br

Pablo Augusto Garcia Agostinho***

pablo.agostinho@ufv.br

*Mestranda/o em Educação Física

pelo Programa de Pós Graduação em Educação Física

Universidade Federal de Viçosa (UPV)

**Graduanda/o em Educação Física (UFV)

***Doutorando em Educação Física

pelo Programa de Pós Graduação em Educação Física (UFV)

(Brasil)

Reception: 07/26/2025 - Acceptance: 01/02/2026

1st Review: 09/20/2025 - 2nd Review: 12/23/2026

Accessible document. Law N° 26.653. WCAG 2.0

Suggested reference: Viana, ISA, Benjamim, MS, Silva, LSG, Bombo, JAL, Lopez, DAM, Vaz, ARC, Mathias, AF, Pires, ACM, & Agostinho, PAG (2026). Eccentric Braking in the Squat with Varied Inertial Loads: a Case Study with 2D Analysis. Lecturas: Educación Física y Deportes, 30(333), 174-188. https://doi.org/10.46642/efd.v30i333.8489

 

Abstract

    Eccentric braking plays a key role in flywheel exercises, contributing to strength gains and neuromuscular control. This case study examined how different inertial loads (0.035, 0.050, and 0.075 kg·m²) affect eccentric braking during the squat, using two-dimensional kinematic analysis. The aim of the study was to examine eccentric overload during the squat exercise under different inertial loads. One participant performed three sets of eight repetitions per load, with two additional reps for flywheel acceleration. Movements were recorded laterally with a digital camera and analysed using Tracker software, referencing the hip joint. Vertical coordinates (Y-axis) were smoothed using a five-point moving average. Velocity and acceleration were derived from the first and second derivatives, respectively. Negative acceleration peaks at the end of the downward motion identified the eccentric braking phase. At 0.035 kg·m², a larger range of motion and higher negative acceleration peaks were found, but with irregular patterns, indicating reduced motor control. The intermediate load (0.050 kg·m²) produced similarly high peaks with greater consistency across cycles. At 0.075 kg·m², movement was more constrained, with slower execution and smaller peaks, but with greater stability and control, suggesting refined motor coordination. These findings demonstrate that increasing inertial load directly influences eccentric braking: lighter loads yield high eccentric force but less control; intermediate loads balance force and stability; heavier loads reduce peak force yet enhance control. This underscores the importance of progressive load selection in flywheel training to match the stimulus to specific training goals.

    Keywords: Muscle strength. Muscle power. Flywheel devices. Eccentric overload. Kinematics.

 

Resumo

    A frenagem excêntrica exerce papel fundamental em exercícios com plataformas inerciais (flywheel), contribuindo para ganhos de força e melhora no controle neuromuscular. Este estudo de caso investigou a influência de diferentes cargas inerciais (0,035, 0,050 e 0,075 kg•m²) sobre o padrão de frenagem excêntrica durante o agachamento, por meio de análise cinemática bidimensional. O objetivo do estudo foi verificar a sobrecarga excêntrica no agachamento com diferentes cargas inerciais. Um voluntário realizou três séries de oito repetições por carga, com filmagem lateral e análise no software Tracker, utilizando o quadril como ponto de referência. As coordenadas verticais foram suavizadas com média móvel de cinco pontos, e a velocidade e aceleração foram obtidas por derivadas sucessivas. A fase de frenagem excêntrica foi identificada pelos picos negativos de aceleração ao fim da fase descendente. Com 0,035 kg•m², houve maior amplitude e picos intensos de aceleração negativa, mas com padrão irregular, indicando menor controle motor. A carga intermediária (0,050 kg•m²) gerou picos elevados com maior regularidade e consistência. Já com 0,075 kg•m², o movimento foi mais contido, com menor velocidade e picos reduzidos, mas padrão mais estável, sugerindo maior refinamento motor. Os resultados indicam que a carga inercial afeta diretamente a estratégia de frenagem excêntrica: cargas leves favorecem força, mas com menor estabilidade; cargas intermediárias equilibram intensidade e controle; cargas altas reduzem a intensidade, mas aumentam a precisão. Tais achados reforçam a importância da progressão adequada de carga no treinamento com flywheel, conforme os objetivos do praticante.

    Unitermos: Força muscular. Potência muscular. Volantes inerciais. Sobrecarga excêntrica. Cinemática.

 

Resumen

    El frenado excéntrico juega un papel clave en ejercicios con plataformas inerciales (flywheel), contribuyendo a ganancias de fuerza y ​​al control neuromuscular. Este estudio de caso examinó cómo diferentes cargas inerciales (0,035, 0,050 y 0,075 kg•m²) afectan el frenado excéntrico durante la sentadilla, utilizando un análisis cinemático bidimensional. El objetivo fue examinar la sobrecarga excéntrica durante el ejercicio de sentadilla bajo diferentes cargas inerciales. Un participante realizó tres series de ocho repeticiones por carga, con dos repeticiones adicionales para la aceleración del volante de inercia. Los movimientos se registraron lateralmente con cámara digital y fueron analizados con el software Tracker, haciendo referencia a la articulación de cadera. Las coordenadas verticales (eje Y) se suavizaron utilizando una media móvil de cinco puntos. La velocidad y la aceleración se derivaron de la primera y la segunda derivada, respectivamente. Los picos de aceleración negativos al final del movimiento descendente identificaron la fase de frenado excéntrico. Con carga de 0,035 kg•m², se observó mayor rango de movimiento y picos de aceleración negativos más altos, pero con patrones irregulares, lo que indica un control motor reducido. La carga intermedia (0,050 kg•m²) produjo picos igualmente altos con mayor consistencia a lo largo de los ciclos. Con una carga de 0,075 kg•m², el movimiento fue más restringido, con ejecución más lenta y picos más pequeños, pero con mayor estabilidad y control, lo que sugiere una coordinación motora refinada. Estos hallazgos demuestran que el aumento de carga inercial influye directamente en el frenado excéntrico.

    Palabras clave: Fuerza muscular. Potencia muscular. Volante de inercia. Sobrecarga excéntrica. Cinemática.

 

Lecturas: Educación Física y Deportes, Vol. 30, Núm. 333, Feb. (2026)

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Introduction 

 

    The squat is a multi-joint exercise widely used in both sports training and rehabilitation, as it simultaneously involves flexion and extension of the hip, knee, and ankle joints. Its execution requires a high degree of inter muscular coordination, particularly during the eccentric phase (descent), where maximum joint flexion angles are typically reached nearly simultaneously (McKean et al., 2010; Schoenfeld, 2010). Loaded squats, such as those performed with a barbell, tend to increase hip and knee flexion and induce greater trunk inclination, especially at intensities near one-repetition maximum (Lorenzetti et al., 2018; Eriksson, 2022). These variations affect the relative effort of major extensor groups, influencing both training stimulus and injury risk. (Strömbäck et al., 2018)

 

    Recently, flywheel resistance training (FRT) has gained attention as an alternative to traditional weight training (WT), particularly due to its capacity to provide significant and adaptable eccentric overload (Moreira et al., 2025; Yánez, Mancera, & Suarez, 2022). Unlike WT, FRT relies on the inertial moment of a rotating disc to generate variable resistance, which depends on the system’s acceleration and deceleration rather than gravity. This characteristic allows for an accentuated eccentric demand during the braking phase of movement, potentially leading to substantial gains in strength, power, hypertrophy, and neuromuscular control. (Maroto-Izquierdo et al., 2017)

 

    FRT has been applied in diverse contexts, from athletic performance to the prevention of muscle atrophy in astronauts during spaceflight (Tesch et al., 2004; Agostinho et al., 2025). However, most studies have focused on single-joint exercises, such as knee extensions, with limited investigation into joint kinematics during multi-joint movements like the squat. In particular, the effects of varying inertial load on eccentric braking patterns and their biomechanical implications remain poorly understood.

 

    In this context, two-dimensional (2D) kinematic analysis emerges as an accessible and effective tool to quantify parameters such as position, velocity, and acceleration throughout the movement, offering indirect insights into motor control and eccentric overload. Evaluating these variables under different inertial loads may help elucidate how the neuromuscular system adapts its braking strategy during exercise.

 

    Therefore, this case study aimed to investigate the effects of different inertial load levels on eccentric braking patterns during the squat exercise, using 2D kinematic analysis. It is suggested that higher loads promote greater stability and motor control, while lighter loads induce greater acceleration peaks but less consistency, contributing to more precise training prescriptions based on specific objectives.

Based on the aforementioned considerations, the objective of the present study is to examine the eccentric overload during the squat exercise under different inertial loads.

 

Methods 

 

    The participant attended a single data collection session at the biomechanics analysis laboratory of the Federal University of Viçosa during their habitual waking hours (between 9:00 and 11:00 a.m.), following a typical night of sleep. Volunteers are instructed to maintain their usual diet and ensure adequate fluid intake in the 24 hours prior to the session to support consistent physiological conditions throughout the experimental protocol.

 

    The study was carried out in the Laboratory for Human Morphophysiology Analysis (Human Lab), part of the Department of Physical Education at the Federal University of Viçosa, after being approved in accordance with all Ethical Guidelines for Research in Exercise and Sport Sciences (Resolution 510/2016) and aligned with the principles of the Declaration of Helsinki. Furthermore, the ethical procedures were reviewed and approved by the Human Research Ethics Committee of the Federal University of Viçosa under protocol number CAAE: 93793118.1.0000.5153. Data collection only began after approval from the aforementioned committee.

 

    The participant was already familiar with the flywheel device, minimizing potential learning effects and ensuring greater consistency in movement execution. Kinematic data were collected during the performance of squats using the flywheel system.

 

    The exercise was performed on a flywheel device (T-One, Physical Solution, São Paulo, Brazil). The equipment consists of a platform with a vertically oriented flywheel mounted at the front. A cord, attached to a belt or vest worn by the participant, is connected to the flywheel axle through an opening in the platform. The exercise begins from a fully flexed position (deep squat), corresponding to the lowest point of the range of motion. During the concentric phase, the participant stands up, initiating the rotation of the flywheel (see x 1). Subsequently, during the eccentric phase, the rotating flywheel maintains its accumulated momentum, requiring the participant to decelerate the movement via eccentric muscle contractions. The following repetition occurs continuously, with the flywheel spinning in the opposite direction.

 

Source: Kinematic Data Collection

 

    Kinematic data were collected through video recording of the exercise. A digital camera was positioned laterally (sagittal plane) on a fixed tripod, perpendicular to the direction of movement. The recording aimed to capture the vertical displacement of the participant’s hip, which was used as the reference point for tracking. The video was then imported into Tracker, an open-source software designed for motion analysis in videos.

 

    Before tracking, a scale calibration was performed using a reference object (1 meter in length) visible on the wall within the frame, allowing the conversion of pixel values to meters.

 

    Manual frame-by-frame tracking was carried out to register the vertical position of the hip over time. Time and position data were exported in .csv format for further analysis in Microsoft Excel. From these data, derived variables of velocity and acceleration were calculated. Vertical velocity was obtained by computing the change in position between two consecutive frames divided by the time interval, while acceleration was derived from the change in velocity over time.

 

    To reduce noise resulting from manual tracking, the data were smoothed using a simple moving average over five consecutive points. Additionally, extreme values deemed non-physiological (e.g., those exceeding 12 m/s or m/s²) were identified and removed using conditional formulas, with these points replaced by blank cells (see Figure 2).

 

Note: Vertical velocity calculation (v): v = vertical velocity (m/s), ΔS = change in vertical position (m), Δt = time interval between frames (s); Vertical acceleration calculation (a): a = vertical acceleration (m/s²), ΔV = change in velocity (m/s), Δt = time interval between frames (s); Data smoothing (simple moving average): x̄ᵢ = smoothed value at point i, xᵢ₋₂, xᵢ₋₁, xᵢ, xᵢ₊₁, xᵢ₊₂ = values of position, velocity, or acceleration from the five adjacent frames used in the moving average.

 

    Using the processed data, graphs were generated to represent position, velocity, and acceleration as functions of time. The analysis focused on the eccentric phase of the movement (downward phase of the squat), identified by the negative sign of vertical velocity. Eccentric braking capacity was assessed based on the peak of positive acceleration following a phase of increasingly negative velocity, indicating the effort required to decelerate the downward movement. The time between the peak negative velocity and the subsequent positive acceleration peak (braking time), as well as the magnitude of acceleration within this interval, were evaluated as indicators of eccentric motor control efficiency.

 

Results 

 

    The following figures present the analysis of kinematic variables (position, velocity, and acceleration) as functions of time under different inertial load conditions applied to the squat platform. The aim was to observe how a gradual increase in load influenced movement behaviour across the executed cycles.

 

Source: Research data

 

    Figure 3 shows the graphs obtained using the inertial load of 0.035 kg•m². The velocity displays well-defined cyclic variations, with abrupt directional changes characteristic of repetitive movement. In contrast, the acceleration exhibits more irregular and higher-intensity peaks, suggesting greater sensitivity to small variations in motor control. These data indicate an active, dynamic behaviour, with significant variation in the forces involved, even under a light load.

 

Source: Research data

 

    In Figure 4, the graphs refer to the 0.050 kg•m² load. The velocity displays more moderate peaks and greater symmetry between cycles, suggesting improved control of the movement. Acceleration, in turn, shows a reduction in peak values and a smoother overall pattern compared to the graph for the 0.035 kg•m² load. This may indicate a neuromuscular adaptation to the slightly higher load, promoting greater stability in the motor pattern.

 

Source: Research data

 

    Finally, Figure 5 presents the results obtained with the load of 0.075 kg•m². The velocity curve shows broader and more defined variations, indicating higher demand during the movement. The acceleration reveals peaks of greater intensity, both positive and negative, suggesting increased oscillation in the forces generated. These findings indicate that the higher inertial load imposed greater demand on the motor system, resulting in more pronounced variations in the analysed variables.

 

Discussion 

 

    The present case study aimed to investigate the influence of different magnitudes of inertial load on the eccentric braking pattern during the squat exercise performed on a flywheel platform, through two-dimensional kinematic analysis. The main findings showed that inertial load significantly impacts the eccentric deceleration strategy, altering the magnitude, regularity, and control of the movement.

 

    Light loads (0.035 kg•m²) favoured the generation of high peaks of negative acceleration, albeit with a more irregular pattern, suggesting lower motor control. Intermediate loads (0.050 kg•m²) maintained high acceleration peaks but with greater regularity, while higher loads (0.075 kg•m²) showed lower magnitudes of negative acceleration but a more stable and controlled braking pattern.

 

    The literature partially supports these findings, indicating that increasing inertial load tends to reduce the maximum angular velocity at the knee and hip joints without significantly altering the maximum joint angles in the sagittal plane during flywheel resistance training squats (Brien et al., 2022; Ryan et al., 2023). This suggests that despite the speed reduction, joint range of motion is maintained, which may benefit technique and joint safety under higher loads.

 

    The observed decrease in velocity with increased inertia in this study, evidenced by the derivative of the vertical coordinates, aligns with previous studies reporting reductions in mean power and vertical velocity with higher inertial loads (Spudić et al., 2021). This behaviour seems to reflect slower joint rotations at the hip and knee, while trunk inclination remains stable (Faigenbaum, & Myer, 2010; Myer et al., 2014; Sjöberg et al., 2022), which may indicate less lumbar overload compared to barbell squats, where axial load is higher.

 

    The more stable braking pattern with the 0.075 kg•m² load may be related to the need for more refined neuromuscular control in the final eccentric phase, where the greatest deceleration occurs. Although maximum joint angles did not change significantly, the lower variability in negative acceleration peaks may indicate better eccentric control, a key aspect for the safe prescription and efficacy of FRT in rehabilitation or athletic performance contexts.

 

    Thus, the evidence suggests that intermediate loads (around 0.050 kg•m²) offer a balance between power production, kinematic stability, and motor control. This result aligns with studies showing that light to moderate loads optimize power output in flywheel exercises, while very low loads favour velocity but with greater variability, and very high loads reduce total power. (Norrbrand et al., 2008; Petré et al., 2018)

 

    The choice of inertial load should be guided by training objectives: Lower loads can be used for maximal eccentric force stimuli and neural adaptations; higher loads favour stability, postural control, and movement precision, contributing to muscle strength development.

 

    Our work presents an important limitation: the lack of monitoring of velocity during the concentric phase of the movement, a critical factor for neuromuscular and hypertrophic adaptations, especially in inertia-based training. As highlighted by Wang et al. (2025), real-time monitoring technologies are strongly recommended to ensure greater precision in exercise execution.

 

Conclusion 

 

    This case study demonstrated that different inertial loads significantly influence the eccentric braking strategy during squats on a flywheel platform, affecting movement speed and regularity without altering maximum joint angles. Light loads produced higher peaks of negative acceleration but with less control, while higher loads provided greater stability. These findings highlight the importance of individualized load prescription in FRT according to strength, power, or motor control goals, further suggesting its potential as a safe tool in rehabilitation and injury prevention contexts.

 

Practical applications 

 

    Based on the observed results, the appropriate selection of inertial load in flywheel resistance training squats should consider the balance between eccentric demand and motor control. The sagittal plane mechanics were largely preserved within the range of 0.050-0.075 kg•m², even with variation in execution speed. This indicates that the exercise can be safely applied in contexts requiring postural control and segmental stability, such as rehabilitation or return to sport.

 

    Interventions aimed at developing joint velocity, especially at the knee and hip, may optimize power performance without compromising movement safety, particularly with intermediate loads that provide a good combination of eccentric demand and kinematic consistency.

 

Acknowledgments 

 

    This work was supported by the Pro-Rectory of People Management (PGP), with two scholarships, and we thank the Human Lab and Lab Biomechanics Analysis UFV laboratories for their support throughout this work.

 

Study limitations 

 

    As study limitations, the following can be noted: the use of a single-participant sample; the performance of only one data collection session, which may limit the measurement and interpretation of the velocity factor; and the lack of more illustrative images of the movement.

 

References 

 

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Brien, J., Browne, D., Earls, D., & Lodge, C. (2022). The effects of varying inertial loadings on power variables in the flywheel Romanian deadlift exercise. Biology of Sport, 39(3), 499-503. https://doi.org/10.5114/biolsport.2022.106159

 

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Lecturas: Educación Física y Deportes, Vol. 30, Núm. 333, Feb. (2026)