The Influence of Strength in Load-Velocity Relationships in the Back Squat

Load-velocity relationships may vary between people of different strength levels and across different loads. The purpose of this dissertation was to investigate how external loads influence the velocity characteristics of the back squat exercise, and the influence of strength on these variables. Healthy male students with a history of resistance training completed repetitions at specified intensities of their estimated one-repetition maximum (1RM) until they reached 1RM. Back squat 3D motion analysis was captured using four Vicon T010 cameras (Vicon Motion Systems Ltd.; Oxford, UK) and Vicon Nexus 1.8.5 software. Data were transported into R custom coding statistical analysis software (version 3.5.2; The R Foundation) to calculate velocity analyses which determined mean and peak concentric (MCV, PCV) and eccentric (MEV, PEV) values. Participants were grouped by their relative strength (body mass/1RM) in the back squat, as well as their ability to move often prescribed loads with greater speed (63-70%1RM, 83-87%1RM). Between-groups comparisons were made for MCV at all loading conditions, and correlational relationships between all velocity measures (MEV, PEV, MCV, PCV) were examined for each group. For all subjects, there was a significant effect for relative intensity (%1RM) on MCV, but only for the groups organized by MCV at 63-70%1RM and 83-87%1RM was there a between-subjects effect for group. Correlational analyses between velocity measurements during concentric and eccentric phase of the back squat showed a tendency for high relationships (r = 0.5-0.69) between all phases that weakened as the relative intensity increased. These differences were illustrated uniquely between subject grouping conditions. These results indicate that load-velocity characteristics of the back squat cannot necessarily be positively related to strength level in the movement, and that profiling athletes by their velocities at specific relative intensities could be an effective means of organization

Lumbar spine kinematics and kinetics during heavy barbell squat and deadlift variations

Purpose: The primary purpose of this research was to compare barbell deadlifts and squats, as well as two technique variations within each lift, for their effects on lumbar spine kinematics and kinetics. The techniques compared within the deadlift condition were the low-hip deadlift (LHDL) and the high-hip deadlift (HHDL). The techniques compared within the squat condition were the high-bar squat (HBS) and low-bar squat (LBS). The outcome variables measured were peak lumbar flexion, L4-L5 and L5-S1 moments, and L5-S1 joint reaction force. Methods: Data were collected and reported on 17 healthy competitive strength athletes (male = 12, female = 5, age = 26.5 ± 4.7 years, height = 176.1 ± 4.6 cm, body mass = 97.7 ± 22.3 kg). Participants completed three single lifts at 85% of their estimated one-repetition maximum using each lifting technique during a single session. Data were collected using an 8-camera 3D motion capture system and two in-ground force plates then processed using custom Matlab routines. Lumbar flexion was calculated using a custom kinematic driven lumbar spine model. Joint moments were calculated using inverse dynamics. Joint reaction force calculations were based on an equilibrium approach using a single-equivalent muscle model. A 2×2 factorial ANOVA with the factors of lift type (deadlift vs squat) and bar position (anterior vs posterior) was used to determine the effect of each main lift on the outcome variables. Significance for the ANOVA was set at p<.01. Planned paired samples t-test’s were used to compare the effects of lift technique (LHDL vs HHDL and HBS vs LBS) on the outcome variables. Significance was set at p<01. Results: Peak lumbar flexion, expressed as a percentage of maximal voluntary flexion, was significantly greater during the deadlift condition (76.76 ± 16.07%) in comparison to the squat condition (64.2 ± 19.8%, p = .005). Within the squat condition, peak lumbar flexion was significantly greater for the LBS technique (67.9 ± 19.7%) when compared to the HBS technique (60.43% ± 19.79, p<.001). Normalized L5-S1 joint reaction force results displayed that within the deadlift condition, there was significantly greater average shear force during the LHDL technique (2.02 ± 0.23N) in comparison to the HHDL technique (1.98 ± 0.22N, p=.004). Within the squat condition, there was significantly greater peak shear force during the HBS technique (2.59 ± 0.42N) in comparison to the LBS technique (2.47 ± 0.40N, p<.001). Significant differences were not observed between or within lifting conditions for any of the other variables. Conclusion: This is the first study to directly compare lumbar flexion and L5-S1 joint reaction forces between the barbell deadlift and squat, as well as the HHDL/LHDL and HBS/LBS technique variations within each lift. Results suggest that if normalized to barbell load, barbell squats create equivalent loading at the L5-S1 joint when compared to the deadlift. They also suggest significant differences in peak lumbar flexion and peak shear joint reaction force when comparing the HBS and LBS. Past research on barbell squat kinematics have perpetuated the assumption that the torso remains relatively rigid during this exercise; however, these findings indicated the lumbar spine undergoes considerable flexion when squatting to a depth slightly below parallel. Furthermore, the amount of lumbar flexion taking place seems to be influenced by the squat technique used and this can lead to significant differences in peak L5-S1 shear joint reaction force, a variable believed to be related to low back injury

The Validity of The VmaxPro during Countermovement Jump and Back Squat Performance

Background: Advances in technology have resulted in an increase in the utilization of velocity-based training in the strength and conditioning field while utilization of inertia measurement units (IMUs) shows promise. Methods: Recreationally trained participants (N=25, 28.3 ± 2.9 years) were recruited to determine the validity of the VmaxPro device for measuring performance variables in the back squat and countermovement jump (CMJ) against a gold standard force plate. Squat variables assessed included mean concentric velocity (MCV), mean concentric power (MCP), depth, and duration while CMJ variables assessed included MCV, MCP, depth, duration, and jump height. Squat variables were assessed across 3 conditions: BW, 50% BW, and 100% BW. Results: MCV demonstrated strong correlations in the BW, 50% and 100% conditions (r= 0.965; r=.907; r= 0.827, pp pConclusion:The VmaxPro is a reasonably valid device for assessing duration and jump height when assessing CMJ performance as compared to the force plate while demonstrating overestimation bias. For back squat performance variables, the VmaxPro proves as a reasonably valid device for assessing MCV, MCP, depth, and duration while demonstrating overestimation bias in MCV and MCP

Analysis of the backpack loading efects on the human gait

Gait is a simple activity of daily life and one of the main abilities of the human being. Often during leisure, labour and sports activities, loads are carried over (e.g. backpack) during gait. These circumstantial loads can generate instability and increase biomechanicalstress over the human tissues and systems, especially on the locomotor, balance and postural regulation systems. According to Wearing (2006), subjects that carry a transitory or intermittent load will be able to find relatively efficient solutions to compensate its effects.info:eu-repo/semantics/publishedVersio

Acute effects of suspension training and other perturbative sources on lower limb strength tasks

Actualment, els dispositius de suspensió són un dels materials més utilitzats per produir pertorbació i enfortir de forma global la majoria de grups musculars. Encara que, manquen evidències dels seus efectes sobre l’extremitat inferior. Així, l’objectiu principal d’aquesta tesi doctoral va ser quantificar la producció de força, l’activitat muscular i la magnitud de la pertorbació a l’esquat búlgar i altres exercicis de l’extremitat inferior en condicions d’inestabilitat. Es van analitzar 18 estudis per dur a terme una revisió sistemàtica (estudi 1) i 75 participants físicament actius van ser reclutats per realitzar els diferents estudis transversals sobre els efectes dels dispositius de suspensió, les superfícies inestables i les vibracions mecàniques (plataforma vibratòria i vibració superposada) en exercicis de l’extremitat inferior (estudis 2-6). Es va confirmar que l’activació a la part inferior del cos només va ser investigada en el concentrat d’isquiosurals en suspensió (estudi 1). La posició i el ritme d’execució (70 bpm) van ser determinants per la producció de força exercida sobre el tirant de suspensió a l’esquat búlgar (estudi 2). El dispositiu de suspensió a l’esquat búlgar va augmentar les forces verticals contra el terra (estudi 3). Sobre el dispositiu la producció de força va ser major quan el nivell d’inestabilitat era baix (estudi 3 i 4), però a nivell muscular el dispositiu va ser igual de demandant que l’exercici tradicional (estudi 3). Un augment de la pertorbació, va incrementar l’activació muscular (estudis 3, 4, 5) i la magnitud de la inestabilitat per l’esquat búlgar i el mig squat amb barra (estudis 4 i 5). Així, la vibració superposada en un dispositiu de suspensió esdevé un repte per incrementar el nivell de pertorbació i millorar la força, la resistència muscular i l’estabilització (estudi 6). A més, els sensors de força són una eina adequada i usable per valorar les forces exercides sobre els dispositius de suspensió, i l’ús de l’acceleròmetre permet determinar la magnitud de la pertorbació que ofereixen els diferents materials desestabilitzadors mesurant l’acceleració del centre de masses corporal.Actualmente, los dispositivos de suspensión son uno de los materiales más utilizados para producir perturbación y fortalecer globalmente la mayoría de los músculos. Aunque, faltan evidencias de sus efectos sobre la extremidad inferior. Así, el objetivo principal de esta tesis doctoral fue cuantificar la producción de fuerza, la actividad muscular y la magnitud de la perturbación en la sentadilla búlgara y otros ejercicios de la extremidad inferior en condiciones de inestabilidad. Se analizaron 18 estudios para llevar a cabo una revisión sistemática (estudio 1) y 75 participantes físicamente activos fueron reclutados para realizar los diferentes estudios transversales sobre los efectos de los dispositivos de suspensión, las superficies inestables y las vibraciones mecánicas (plataforma vibratoria y vibración superpuesta) en ejercicios de la extremidad inferior (estudios 2-6). Se confirmó que la activación en la parte inferior del cuerpo sólo fue investigada en el concentrado de isquiosurales en suspensión (estudio 1). La posición y el ritmo de ejecución (70 bpm) fueron determinantes para la producción de fuerza ejercida sobre el tirante de suspensión en la sentadilla búlgara (estudio 2). El dispositivo de suspensión en la sentadilla búlgara aumentó las fuerzas verticales contra el suelo (estudio 3). Sobre el dispositivo la producción de fuerza fue mayor cuando el nivel de inestabilidad era bajo (estudio 3 y 4), pero a nivel muscular el dispositivo fue igual de demandante que el ejercicio tradicional (estudio 3). Un aumento de la perturbación incrementó la activación muscular (estudios 3, 4, 5) y la magnitud de la inestabilidad en la sentadilla búlgara y la media sentadilla con barra (estudios 4 y 5). Así, la vibración superpuesta en un dispositivo de suspensión se convierte en un reto para incrementar el nivel de perturbación y mejorar la fuerza, la resistencia muscular y la estabilización (estudio 6). Además, los sensores de fuerza son una herramienta adecuada y usable para valorar las fuerzas ejercidas sobre los dispositivos de suspensión, y el uso del acelerómetro permite determinar la magnitud de la perturbación que ofrecen los diferentes materiales desestabilizadores midiendo la aceleración del centro de masas corporal.Nowadays, suspension devices are one of the most widely used pieces of equipment to produce perturbation and strengthen most muscle groups globally. However, there is a lack of evidence of their effects on the lower limb. Thus, the main objective of this doctoral thesis was to quantify force production, muscle activity and the magnitude of perturbation in the Bulgarian squat and other lower extremity exercises under unstable conditions. Eighteen studies were analysed for a systematic review (study 1) and 75 physically active participants were recruited to perform the different cross-sectional studies on the effects of suspension devices, unstable surfaces, and mechanical vibrations (vibration platform and superimposed vibration) on lower limb exercises (studies 2-6). It was confirmed that lower body activation had only been previously investigated in the suspended hamstring curl (study 1). Position and pace (70 bpm) were determinants for the force exerted on the suspension strap in the Bulgarian squat (study 2). The suspension device in the Bulgarian squat increased the vertical ground reaction forces (study 3). The force production was higher on the device when the level of instability was low (study 3 and 4), but for muscle activity the device was just as demanding as a traditional exercise (study 3). Increased perturbation enhanced muscle activation (studies 3, 4, 5) and the magnitude of instability in the Bulgarian squat and barbell half-squat (studies 4 and 5). Thus, superimposed vibration on a suspension device becomes a challenge to increase the level of perturbation and improve strength, muscular endurance, and stabilisation (study 6). In addition, load cells are a suitable and practical tool to assess the forces exerted on suspension devices, and the use of an accelerometer makes it possible to determine the magnitude of the perturbation offered by different equipment providing instability by measuring the acceleration of the body's centre of mass

The efficacy of the load-velocity profile to predict one repetition maximum

Autoregulation is the process of acutely manipulating training variables in response to an individual’s fluctuations in strength and fatigue and is vital for optimising programming. Load-velocity profiles (LVPs) have been proposed as effective flexible programming strategies to optimise resistance training load (kg), often through the daily estimation of one repetition maximum (1RM). This PhD, therefore, adopted a pragmatic, mixed methods research design and followed an applied research model (ARMSS) to devise a series of studies to ascertain a novel, efficient, and valid approach to LVP-based 1RM prediction. Prior to choosing an autoregulatory method, strength and conditioning (S&C) practitioners must first determine an appropriate non-flexible programming strategy. A systematic review of literature revealed percentages of 1RM (% 1RM) as the superior method for increasing maximal strength (study one). After thematic analyses (study two) revealed barriers such as inaccurate 1RM predictions, time-costly protocols, and “iPad coaching” to the implementation of LVPs within practice; common velocity-based technology used by coaches; and the combination of ballistic and non-ballistic exercise when profiling, a new LVP method addressing these factors was devised in a key training, but under-researched exercise, the free-weight back squat. The new approach to LVP-based 1RM prediction developed from this thesis utilised the Gymaware linear-position transducer given its superior reliability and validity (study three); individualised profiling due to stronger load-velocity relationships and large between-participant variability observed (study four); ballistic (jump squat) exercise after larger mechanical output was revealed in 0-60% 1RM when compared to non-ballistic (back squat) (study five); a submaximal point of extrapolation (80% 1RM mean velocity) due to poor within-participant reliability of loads > 85% 1RM (study four); quadratic modelling (study four); and as few as four incremental loads. Results revealed this combination to be an effective method for estimating 1RM and autoregulating daily load for S&C coaches

The EMG profiles of 3 lower body resistance exercises

Introduction: Resistance training has previously been demonstrated to contribute to the improvement of athletic performance. The back squat and deadlift have both been heavily researched in the field of sEMG but remain complex exercises. The hip thrust however is a much simpler exercise, which loads the bar in a different movement plane. The sEMG activity of these three lifts have previously never been compared against one another in the one study. Aim: The primary aim of the study was to establish and compare sEMG profiles of the lower leg musculature. During the concentric phase of the back squat, deadlift and hip thrust, in non - resistance trained individuals (n=22), in maximal and sub – maximal efforts. Methods: Participants completed 2 separate testing sessions, 7 days apart. The first, acted as a normalisation to testing procedures with no data collection, where participants underwent 1RM testing with sEMG electrodes placed at 4 regions of the lower limb musculature: the upper and lower Gluteus Maximus, Vastus Lateralis and Bicep Femoris. The second session again required 1RM testing, but this time also recorded sEMG data in maximal and submaximal efforts. Results: Analysis of peak sEMG in the 1RM and 85 % of 1RM found there to be no difference in gluteal activation between the three lifts. Further analysis through coding split the concentric phase of the lift into three equal tertiles. This allowed for the comparison of sEMG amplitude throughout the concentric phase. Analysis of the 1RM tertiles data found that the deadlift had a significantly greater level of sEMG activity when compared to the squat and hip thrust. Conclusions: The data suggests that any of these 3 exercises would effectively target the gluteus muscles. However, the deadlift seems to result in greater electrical activity at the selected sites out of the three exercises