Analysis of the Load on the Knee Joint and Vertebral Column with Changes in Squatting Depth and Weight Load

Combined Accentuated Eccentric Loading and Rest Redistribution in High-Volume Back Squat: Acute Kinetics and Kinematics

ABSTRACT

Chae, S, Long, SA, Lis, RP, McDowell, KW, Wagle, JP, Carroll, KM, Mizuguchi, S, and Stone, MH. Combined accentuated eccentric loading and rest redistribution in high-volume back squat: Acute kinetics and kinematics. J Strength Cond Res 38(4): 640-647, 2024-The purpose of this study was to explore acute kinetic and kinematic responses to combined accentuated eccentric loading and rest redistribution (AEL + RR). Resistance-trained men ( n = 12, 25.6 ± 4.4 years, 1.77 ± 0.06 m, and 81.7 ± 11.4 kg) completed a back squat (BS) 1 repetition maximum (1RM) and weight releaser familiarization session. Three BS exercise conditions (sets × repetitions × eccentric/concentric loading) consisted of (a) 3 × (5 × 2) × 110/60% (AEL + RR 5), (b) 3 × (2 × 5) × 110/60% (AEL + RR 2), and (c) 3 × 10 × 60/60% 1RM (traditional sets [TS]). Weight releasers (50% 1RM) were attached to every first repetition of each cluster set (every first, third, fifth, seventh, and ninth repetition in AEL + RR 5 and every first and sixth repetition in AEL + RR 2). The AEL + RR 5 resulted in significantly ( p < 0.05) greater concentric peak velocity (PV) (1.18 ± 0.17 m·s -1 ) and peak power (PP) (2,304 ± 499 W) compared with AEL + RR 2 (1.11 ± 0.19 m·s -1 and 2,148 ± 512 W) and TS (1.10 ± 0.14 m·s -1 and 2,079 ± 388 W). Furthermore, AEL + RR 5 resulted in significantly greater PV and PP across all 10 repetitions compared with TS. Although AEL + RR 5 resulted in significantly greater concentric mean force (MF) (1,706 ± 224 N) compared with AEL + RR 2 (1,697 ± 209 N) and TS (1,685 ± 211 N), no condition by set or repetition interactions existed. In conclusion, AEL + RR 5 increases PV and PP but has little effect on MF. Coaches might consider prescribing AEL + RR 5 to increase especially peak aspects of velocity and power outcomes.

Biomechanical comparisons of back and front squats with a straight bar and four squats with a transformer bar

The purpose was to quantify trunk and lower extremity biomechanics among back and front squats with a straight bar and four squats with different anterior-posterior load placements imposed by a transformer bar. Ten males and eight females performed six squat conditions: back and front squats with a straight bar, back and front squats with a transformer bar, and squats with more posteriorly or anteriorly placed loads with a transformer bar. A constant load of 70% of the participant's one-repetition maximum in the straight-bar front squat was used. Kinematic and kinetic data were collected to quantify joint biomechanics at an estimated parallel squat position in the descending and ascending phases. Squats with more anteriorly placed load significantly decreased trunk flexion and pelvis anterior tilt angles with large effect sizes but increased low-back extension moments with medium to large effect sizes. Hip, knee, and ankle extension moments were generally similar among most conditions. Participants adjusted their trunk and pelvis to mediate the effects of load placements on low-back and lower extremity moments. While lower extremity loading was similar among different squats, the different trunk and pelvis angles and low-back moments should be taken into consideration for people with low-back impairment.

Finding the Goldilocks Zone of Mechanical Loading: A Comprehensive Review of Mechanical Loading in the Prevention and Treatment of Knee Osteoarthritis

In this review, we discuss the interaction of mechanical factors influencing knee osteoarthritis (KOA) and post-traumatic osteoarthritis (PTOA) pathogenesis. Emphasizing the importance of mechanotransduction within inflammatory responses, we discuss its capacity for being utilized and harnessed within the context of prevention and rehabilitation of osteoarthritis (OA). Additionally, we introduce a discussion on the Goldilocks zone, which describes the necessity of maintaining a balance of adequate, but not excessive mechanical loading to maintain proper knee joint health. Expanding beyond these, we synthesize findings from current literature that explore the biomechanical loading of various rehabilitation exercises, in hopes of aiding future recommendations for physicians managing KOA and PTOA and athletic training staff strategically planning athlete loads to mitigate the risk of joint injury. The integration of these concepts provides a multifactorial analysis of the contributing factors of KOA and PTOA, in order to spur further research and illuminate the potential of utilizing the body's own physiological responses to mechanical stimuli in the management of OA.

The magnitude of correlation between deadlift 1RM and jumping performance is sports dependent

Introduction

Based on the assumption of maximal strength as a basic ability, several studies show a high influence of maximum strength on jumping performance in several sport athletes. However, there is a wide range of correlations from r = 0.17-0.9 between squat 1RM and jumping performance in different sports. Additionally, there are only a few studies investigating the influence of deadlift one repetition maximum (1RM) on jumping performance. Thus, this study aimed to investigate the correlations between 1RM in the deadlift on jumping performance using the countermovement jump height (CMJ) and squat jump height (SJ) considering different sports.

Methods

103 athletes with experience in the deadlift from soccer, basketball, American football, powerlifting as well as participants from different sports without any deadlift experience (control group) were included to this study.

Results

Overall statistics showed a significant moderate influence of deadlift 1RM (r = 0.301-0.472) on jumping performance. However, subgroup analysis showed no significant correlation between deadlift 1RM and jumping performance in control participants, while moderate correlations could be detected in powerlifters (r = 0.34-0.39), soccer players (r = 0.437-0.46), American football players (0.584-0.62) and high correlations in basketball players (r = 0.809-0.848) showing significant influence of type of sport on correlations between deadlift maximum strength and jumping performance.

Discussion

Presented results underline movement velocity- and task specificity of strength training routines which is discussed in the light of the respective sports.

Joint knee loads during squat with constant or variable resistance in males. A clinical trial

BACKGROUND

In the squat movement, the use of constant resistance (CR) generates greater compression and shear forces close to 90° of knee flexion, increasing joint overload. However, when used variable resistance (VR) there is no consensus about the effect of knee joint load. The aim of this study was to compare knee torques using constant or variable resistance during the squat exercise.

METHODS

Twenty-one healthy male subjects (mean age, 24 [SD, 3] years; height, 1.76 [SD, 0.04] m), who practice squats during strength training routine. Were simultaneously record data from the platform force and tridimensional kinematic to obtain torques around knee. 15 repetitions were performed up to maximum knee flexion with the use of variable (RV) or constant (CR) resistance in a single session.

RESULTS

Significant differences regarding the angles only in the sagittal plane at the end of the ascending phase of the squat, with less knee extension in the VR condition. In the sagittal and frontal planes, lower values of extensor and abductor torque were found in the VR condition at the angles of greater knee flexion.

CONCLUSION

The use of variable resistance compared to constant resistance seems to be an alternative to be considered when the objective is to minimize the internal loads on the knee joint in exercises such as the squat in amplitudes of greater flexion. This study indicated that VR helps subjects who are learning the squat movement, enabling the application of this knowledge in physical therapy or physical training clinics.

Movement Velocity as an Indicator of Mechanical Fatigue and Resistance Exercise Intensity in Cross Modalities

Purpose: This study analyzed the acute mechanical response to three workouts of the day (WOD) protocols in as many repetitions as possible (AMRAP), every minute on the minute (EMOM), and for time (FT) models by quantifying the degree of mechanical fatigue induced by popular resistance exercises in the Cross modalities, front squat (FS), and shoulder press (SP). We also analyzed whether the exercises' fastest velocity (Vfastest) could be an objective indicator of relative intensity (%1RM). Methods: Nine trained men performed three FS and SP exercises protocols. The degree of fatigue was quantified by the velocity loss (VL) achieved in both exercises and the velocity loss achieved in the WOD (VLWOD). Results: The VLWOD in the AMRAP, EMOM, and FT protocols was 73.2 ± 10.9%, 61.6 ± 15.1%, and 76.1 ± 8.8%, respectively. In the AMRAP and FT protocol, the Vfastest showed very strong relationships with the %1RM for FS and SP (r = -0.83, -0.75, respectively, p < .01); while in the EMOM protocol, there was a strong relationship between these variables, only for the SP (r = -0.61, p < .05). In the FT protocol, we observed an extremely strong relationship for FS (r = -0.91, p < .001) and very strong (r = -0.71, p < .05) for SP between these variables. Conclusion: Therefore, the AMRAP and FT training models induce the highest degrees of mechanical fatigue in the FS and SP exercises, and the Vfastest is a reliable tool for estimating relative intensity in resistance exercises of Cross modalities.

Prevalence and Pattern of Injuries Across the Weight-Training Sports

Background The prevalence and pattern of injury among weightlifters are insufficiently documented despite these research works. Understanding the injury pattern is crucial for minimizing side effects and maximizing the advantages of weight training. Therefore, the purpose of this study is to determine the frequency and pattern of musculoskeletal injury among weightlifters and to investigate the associations between the prevalence of injury and sociodemographic and training characteristics variables. Methods A descriptive cross-sectional, questionnaire-based study was conducted. An online questionnaire was designed by Google Forms to collect the data by using a self-administered questionnaire. From all health clubs in Taif city, Saudi Arabia, one club was chosen by simple random sampling methodology, where all attendant weightlifters during the study period were contacted to participate in the study. Data was entered on the computer using Microsoft Office Excel 2016 for Windows. Qualitative data was expressed as numbers and percentages, and the Chi-squared test (χ2) was used to assess the relationship between variables. A p-value < 0.05 was considered statistically significant. Results The study included 393 participants, and most respondents fall within the age range of 18-29, accounting for 60.1% of the total. About 27% of participants had a weightlift injury during the last six months. The body parts most injured during weightlifting include the shoulder (7.4%), knee (4.6%), and wrist (3.6%). In terms of the type of injuries sustained, inflammation and pain in the bending of the body (5.9%), torsion (3.6%), ligament tear/muscle tear (3.8%), and stripped-off injuries (2.3%) were reported. Conclusion Musculoskeletal injuries are prevalent among weightlifters due to the nature of the sport and the demands it places on the body. There was no significant association between the injury occurrence with gender, age, or body mass index. However, there was a significant association between the occurrence of injury and weight carried while lifting weights.

Self-Massage Techniques for the Management of Pain and Mobility With Application to Resistance Training: A Brief Review

ABSTRACT

MacLennan, M, Ramirez-Campillo, R, and Byrne, PJ. Self-massage techniques for the management of pain and mobility with application to resistance training: a brief review. J Strength Cond Res 37(11): 2314-2323, 2023-Fascial restrictions that occur in response to myofascial trigger points (MTrP), exercise-induced muscle damage (EIMD), and delayed onset of muscle soreness (DOMS) cause soft tissue to lose extensibility, which contributes to abnormal muscle mechanics, reduced muscle length, and decrements in joint range of motion (ROM) and actively contributes to musculoskeletal pain. Resistance training and in particular, weightlifting movements have unique mobility requirements imperative for movement efficacy and safety with ROM restrictions resulting in ineffective volume and intensity tolerance and dampened force output and power, which may lead to a failed lift or injury. Self-massage (SM) provides an expedient method to promote movement efficiency and reduce injury risk by improving ROM, muscular function, and reducing pain and allows athletes to continue to train at their desired frequency with minimal disruption from MTrPs-associated adverse effects. Thus, the aim of this review was to determine the efficacy of various self-massage tools in managing pain and mobility and to explore the potential benefits of SM on resistance training performance. Many SM devices are available for athletes to manage ROM restrictions and pain, including differing densities of foam rollers, roller massagers, tennis balls, and vibrating devices. To attenuate adverse training effects, a 10-to-20-minute bout consisting of 2-minute bouts of SM on the affected area may be beneficial. When selecting a SM device, athletes should note that foam rollers appear to be more effective than roller massagers, with vibrating foam rollers eliciting an increased reduction to pain perception, and tennis balls and soft massage balls were shown to be efficacious in targeting smaller affected areas.

The Emerging Role of the Mitochondrial Respiratory Chain in Skeletal Aging

Maintenance of mitochondrial homeostasis is crucial for ensuring healthy mitochondria and normal cellular function. This process is primarily responsible for regulating processes that include mitochondrial OXPHOS, which generates ATP, as well as mitochondrial oxidative stress, apoptosis, calcium homeostasis, and mitophagy. Bone mesenchymal stem cells express factors that aid in bone formation and vascular growth. Positive regulation of hematopoietic stem cells in the bone marrow affects the differentiation of osteoclasts. Furthermore, the metabolic regulation of cells that play fundamental roles in various regions of the bone, as well as interactions within the bone microenvironment, actively participates in regulating bone integrity and aging. The maintenance of cellular homeostasis is dependent on the regulation of intracellular organelles, thus understanding the impact of mitochondrial functional changes on overall bone metabolism is crucially important. Recent studies have revealed that mitochondrial homeostasis can lead to morphological and functional abnormalities in senescent cells, particularly in the context of bone diseases. Mitochondrial dysfunction in skeletal diseases results in abnormal metabolism of bone-associated cells and a secondary dysregulated microenvironment within bone tissue. This imbalance in the oxidative system and immune disruption in the bone microenvironment ultimately leads to bone dysplasia. In this review, we examine the latest developments in mitochondrial respiratory chain regulation and its impacts on maintenance of bone health. Specifically, we explored whether enhancing mitochondrial function can reduce the occurrence of bone cell deterioration and improve bone metabolism. These findings offer prospects for developing bone remodeling biology strategies to treat age-related degenerative diseases.

Thoracolumbar and Lumbopelvic Spinal Alignment During the Barbell Back Squat: A Comparison Between Men and Women

Background

Maintaining neutral spinal alignment is considered important when performing the barbell back squat exercise. Since male and female lifters may differ in injury location it is important to examine whether they differ in spinal alignment during the back squat.

Objectives

The study aimed to quantify the spinal alignment in the upper and lower lumbar spine during the barbell back squat exercise in male and female lifters. Secondary aims were to compare alignment during the back squat to standing habitual lumbar spine alignment and determine whether male and female lifters differ in these aspects.

Study Design

Observational, Cross-sectional.

Methods

Competitive power- and weightlifters were recruited and performed three repetitions of the barbell back squat exercise using a load equivalent to 70% of their one-repetition maximum. Spinal alignment and range of motion were measured using inertial measurement units placed on the thoracic, lumbar and sacral spine. Data was presented descriptively and comparisons between men and women as well as spinal alignment in four different positions were done with a factorial repeated measures analysis of variance.

Results

Twenty-three (14 males, 9 females) were included. During execution of the squat, spinal alignment adjustments in the lumbar spine were made in all three planes of movement, compared to the start position, in both male and female lifters. Compared to their standing habitual posture, all lifters adjusted their upper lumbar spine to a less lordotic position when in the start position of the back squat (standing upright with the barbell on their back). Only male lifters assumed a less lordotic alignment in their lower lumbar spine in the start position compared their habitual posture.

Conclusions

Adjustments of spinal alignment, predominantly in the sagittal plane, are made during execution of the back squat in both male and female lifters. Further, lifters adopt a less lordotic alignment with a heavy barbell on their upper back, more so in male than female lifters. In conclusion, it seems that spinal alignment changes noticeably during the barbell back squat.

Level of Evidence

3©The Author(s).

First Insights in the Relationship between Lower Limb Anatomy and Back Squat Performance in Resistance-Trained Males and Females

Identifying key criteria of squat performance is essential to avoiding injuries and optimizing strength training outcomes. To work towards this goal, this study aimed to assess the correlation between lower limb anatomy and back squat performance during a set-to-exhaustion in resistance-trained males and females. Optical motion captures of squat performance and data from magnetic resonance imaging (MRI) of the lower limbs were acquired in eight healthy participants (average: 28.4 years, four men, four women). It was hypothesized that there is a correlation between subject-specific musculoskeletal and squat-specific parameters. The results of our study indicate a high correlation between the summed volume of the hamstrings and quadriceps and squat depth normalized to thigh length (r = -0.86), and a high correlation between leg size and one-repetition maximum load (r = 0.81), respectively. Thereby, a marked difference was found in muscle volume and one-repetition maximum load between males and females, with a trend of females squatting deeper. The present study offers new insights for trainers and athletes for targeted musculoskeletal conditioning using the squat exercise. It can be inferred that greater muscle volume is essential to achieving enhanced power potential, and, consequently, a higher 1RM value, especially for female athletes that tend to squat deeper than their male counterparts.

Immediate and Delayed Effects of Joint Loading Activities on Knee and Hip Cartilage: A Systematic Review and Meta-analysis

BACKGROUND

The impact of activity-related joint loading on cartilage is not clear. Abnormal loading is considered to be a mechanical driver of osteoarthritis (OA), yet moderate amounts of physical activity and rehabilitation exercise can have positive effects on articular cartilage. Our aim was to investigate the immediate effects of joint loading activities on knee and hip cartilage in healthy adults, as assessed using magnetic resonance imaging. We also investigated delayed effects of activities on healthy cartilage and the effects of activities on cartilage in adults with, or at risk of, OA. We explored the association of sex, age and loading duration with cartilage changes.

METHODS

A systematic review of six databases identified studies assessing change in adult hip and knee cartilage using MRI within 48 h before and after application of a joint loading intervention/activity. Studies included adults with healthy cartilage or those with, or at risk of, OA. Joint loading activities included walking, hopping, cycling, weightbearing knee bends and simulated standing within the scanner. Risk of bias was assessed using the Newcastle-Ottawa Scale. Random-effects meta-analysis estimated the percentage change in compartment-specific cartilage thickness or volume and composition (T2 relaxation time) outcomes. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system evaluated certainty of evidence.

RESULTS

Forty studies of 653 participants were included after screening 5159 retrieved studies. Knee cartilage thickness or volume decreased immediately following all loading activities investigating healthy adults; however, GRADE assessment indicated very low certainty evidence. Patellar cartilage thickness and volume reduced 5.0% (95% CI 3.5, 6.4, I² = 89.3%) after body weight knee bends, and tibial cartilage composition (T2 relaxation time) decreased 5.1% (95% CI 3.7, 6.5, I² = 0.0%) after simulated standing within the scanner. Hip cartilage data were insufficient for pooling. Secondary outcomes synthesised narratively suggest knee cartilage recovers within 30 min of walking and 90 min of 100 knee bends. We found contrasting effects of simulated standing and walking in adults with, or at risk of, OA. An increase of 10 knee bend repetitions was associated with 2% greater reduction in patellar thickness or volume.

CONCLUSION

There is very low certainty evidence that minimal knee cartilage thickness and volume and composition (T2 relaxation time) reductions (0-5%) occur after weightbearing knee bends, simulated standing, walking, hopping/jumping and cycling, and the impact of knee bends may be dose dependent. Our findings provide a framework of cartilage responses to loading in healthy adults which may have utility for clinicians when designing and prescribing rehabilitation programs and providing exercise advice.

Chronic Lower Back Pain in Weight Lifters: Epidemiology, Evaluation, and Management

» Chronic lower back pain (LBP) is common in both nonathletes and weight lifters, but the diagnosis and treatment should be approached differently in these 2 populations based on the unique movement patterns causing the pain.» Injury rates of weight lifters are far less than those of contact sports, ranging from 1.0 to 4.4 injuries per 1,000 workout hours. However, the lower back was consistently one of the top 2 injury sites for weight lifters, accounting for anywhere from 23% to 59% of all injuries. LBP was most often associated with the squat or deadlift.» Guidelines for evaluating general LBP are applicable to weight lifters, including a thorough history and physical examination. However, the differential diagnosis will change based on the patient's lifting history. Of the many etiologies of back pain, weight lifters are most likely to be diagnosed with muscle strain or ligamentous sprain, degenerative disk disease, disk herniation, spondylolysis, spondylolisthesis, or lumbar facet syndrome.» Traditional recommended therapies include nonsteroidal anti-inflammatory drugs, physical therapy, and activity modification, which are often insufficient to resolve pain and prevent injury recurrence. Because most athletes will want to continue to lift weights, lifting-specific behavior modifications focused on improved technique and correcting mobility and muscular imbalances are important aspects of management in this patient population.

Musculoskeletal Injuries and Risk Factors in Spanish CrossFit® Practitioners

CrossFit^® Training is a physical and sports-conditioning system based on constantly varied functional movements performed at high intensity. CrossFit^® has been shown to significantly improve general physical performance and body composition. Although there seems to be an association between the practice of CrossFit^® and musculoskeletal injuries, the relationship between CrossFit^® and injury risks has been poorly studied. The main objective of this study was to establish the relationship between CrossFit^® and musculoskeletal injuries. Secondary objectives were the analysis of various risk factors and injury and the comparison of the incidence of CrossFit^® injuries to that of other sports. An online questionnaire was distributed to gyms affiliated with CrossFit^®, Inc. in the Principality of Asturias, Spain in order to carry out a retrospective transversal descriptive study. The frequency of injuries in CrossFit^® is similar to most sports. Injuries are often minor and of short duration, with the shoulder being the most affected joint complex.

The Limitations of Anterior Knee Displacement during Different Barbell Squat Techniques: A Comprehensive Review

Based on seminal research from the 1970s and 1980s, the myth that the knees should only move as far anterior during the barbell squat until they vertically align with the tips of the feet in the sagittal plane still exists today. However, the role of both the hip joint and the lumbar spine, which are exposed to high peak torques during this deliberate restriction in range of motion, has remained largely unnoticed in the traditional literature. More recent anthropometric and biomechanical studies have found disparate results regarding anterior knee displacement during barbell squatting. For a large number of athletes, it may be favorable or even necessary to allow a certain degree of anterior knee displacement in order to achieve optimal training outcomes and minimize the biomechanical stress imparted on the lumbar spine and hip. Overall, restricting this natural movement is likely not an effective strategy for healthy trained individuals. With the exception of knee rehabilitation patients, the contemporary literature suggests it should not be practiced on a general basis.

Efficacy of Perilla frutescens (L.) Britton var. frutescens extract on mild knee joint pain: A randomized controlled trial

Objectives: This study aimed to evaluate the clinical efficacy and safety of PE extracts developed for the purpose of relieving pain and improving knee joint function on semi-healthy people with mild knee joint pain.

Methods: A randomized, double-blind, two-arm, single-center, placebo-controlled clinical trial was conducted. Individuals with knee joint pain and a visual analogue scale (VAS) score &lt; 50 mm were included in the study, and participants with radiological arthritis were excluded. Participants were administered either PFE or a placebo capsule (700 mg, twice a day) orally for eight weeks. The comparisons of the changed VAS score and Western Ontario and McMaster Universities Osteoarthritis (WOMAC) scores between the PFE and placebo groups were primary outcomes, while the five inflammation-related laboratory tests including cartilage oligomeric matrix protein, cyclooxygenase-2, neutrophil and lymphocyte ratio, high sensitive C-reactive protein, and erythrocyte sedimentation rate were secondary outcomes. Also, a safety assessment was done.

Results: Eighty participants (mean age, 38.4 ± 14.0, male: female, 28:52) were enrolled; 75 completed the trial (PFE 36 and placebo 39). After eight weeks, both VAS and WOMAC scores were reduced in the PFE and placebo groups. The changed scores were significantly higher in the PFE group compared to the placebo group: 19.6 ± 10.9 vs. 6.8 ± 10.5; VAS scores (p &lt; 0.001), and 20.5 ± 14.7 vs. 9.3 ± 16.5; total WOMAC scores (p &lt; 0.01) including the sub-scores for pain, stiffness, and functions. No significant changes were reported in the five inflammation-related laboratory parameters. All adverse events were considered minor and unlikely to result from the intervention.

Conclusion: Eight weeks of PFE intake was more effective than placebo in reducing knee joint pain and improving knee joint function in sub-healthy people with mild knee joint pain, and there were no major safety concerns.

Clinical Trial Registration:https://cris.nih.go.kr/cris/search/detailSearch.do?search_lang=E&amp;focus=reset_12&amp;search_page=M&amp;pageSize=10&amp;page=undefined&amp;seq=23101&amp;status=5&amp;seq_group=19745, identifier CRIS: KCT0007219

Clustered Associations between Musculoskeletal Fitness Tests and Functional Movement Screen in Physically Active Men

Functional Movement Screen (FMS) is a tool used to assess fundamental movement patterns. There are relationships between musculoskeletal fitness (MSF) and a FMS. However, there is limited data regarding the multidimensional associations between these two constructs. This study is aimed at investigating the associations and detailed structures of FMS components and MSF components and identifying a deeper detailed structure of their relations to physical fitness. The study sample included 114 physically active men with an average body height of 1.81 ± 0.07 (cm), body weight of 80.61 ± 9.49 (kg), and a BMI of 24.65 ± 2.46 (kg/m²). Each participant performed a FMS test, sit-and-reach (S&R) test, sit-ups (ABS) evaluation, balance evaluation on an AMTI platform, handgrip strength (HG) testing, and standing broad jump (SBJ) ability. The Kendall's Tau correlation was performed to identify simple associations between FMS and MSF. Cluster analysis was used to determine the multidimensional nature of the relationships. In the vast majority, a positive correlation was observed suggesting that a high level of MSF improved FMS test results. A cluster analysis revealed 4 separate clusters. Shoulder mobility (SM) was identified as a single cluster. A strong similarity was observed between SBJ and trunk stability push-up (TSPU) forming a second cluster. This cluster joined to another consisting of the S&R test and active straight leg raise (ASLR) test. The last cluster consisted of HG and hurdle step (HS). These results confirmed that FMS and MSF tests measure the same constructs-a foundation for an individual's motor coordination, muscle strength, postural stability, and dynamic balance. This knowledge could be helpful in effectively enhancing physical performance based on combining similar constructs to accelerate the achievement of established goals.

Effects of Knee Extension Joint Angle on Quadriceps Femoris Muscle Activation and Exerted Torque in Maximal Voluntary Isometric Contraction

This study investigated the effects of knee joint angle on muscle activation, exerted torque, and whether the knee angle affects the muscle activation−torque ratio. Nine healthy adult male participants participated in the study. They performed maximal voluntary isometric contraction (MVIC) at six (80°, 90°, 100°, 110°, 120°, and 130°) different knee joint angles (i.e., angles between the thigh and shin bones). Their maximal torque was assessed utilizing an isokinetic chair, while their muscle activation (root mean square [RMS]) was assessed using an eight-channel single differential surface EMG sensor. For the purposes of the torque−knee angle relationship and muscle activation−knee angle relationship, the torque and RMS were normalized relative to the maximal value obtained by each participant. To evaluate the muscle activation−torque ratio in function of knee angle, RMS was normalized relative to the corresponding torque obtained at each knee angle. Repeated measure analysis of variance was used to investigate the effects of knee angle on muscle activation, torque, and muscle activation−torque ratio. There was a significant effect of knee joint angle on normalized torque (F = 27.521, p < 0.001), while the activation of vastus lateralis and vastus medialis remained unchanged. The changes in knee angle affected the muscle activation−torque ratio of vastus lateralis (Chi-square = 16.246, p = 0.006) but not the vastus medialis. These results suggest that knee joint angles from 80° to 130° provide a stable milieu for muscle electrification, while mechanical factor such as knee joint angle (i.e., lever arm length) affect the torque output when one needs to contract quadriceps maximally during the isometric contraction.

Relationship between Dynamic and Isometric Strength, Power, Speed, and Average Propulsive Speed of Recreational Athletes

The purpose of this study was to examine the type of relationship between measures of maximal force (dynamic and isometric), maximal power, and mean propulsive velocity. In total, 355 recreational athletes, 96 women (age 20.5 ± 2.5 years; height 158.2 ± 17.3 cm; weight 61.8 ± 48.4 kg) and 259 men (age 21.0 ± 2.6 years; height 170.5 ± 12.6 cm; weight 65.9 ± 9.2 kg) were evaluated in three sessions separated by 72 h each in isometric midthigh pull exercise (ISOS) (kg), bench press maximum strength (1RM MSBP) (kg), jump height (CMJ) (m), and maximum pedaling power (WT) the maximum squat strength (1RM MSS) (kg), the mean propulsive velocity in the bench press (MPVBP) (m·s^-1), and the peak power (PPBP) (w), mean propulsive squat velocity (MPVS) (m·s^-1), peak power (PP) (w), maximum handgrip force (ISOHG) (kg), and 30 m movement speed (V30) (s). Significant correlations (p ≤ 0.01) were identified between 95% of the various manifestations of force, and only 5% presented a significance of p ≤ 0.05; however, when the magnitude of these correlations is observed, there is great heterogeneity. In this sense, the dynamic strength tests present the best correlations with the other strength and power tests used in the present study, followed by PPBP and PP. The results of this study complement what is reported in the literature regarding the correlation between different types of force manifestations being heterogeneous and contradictory.

Different squatting positions after total knee arthroplasty: A retrospective study

BACKGROUND

Total knee arthroplasty (TKA) has been shown to improve quality of life and reduce pain. High-flexion activities such as squatting, kneeling, and floor transfers are mainly listed as demanding tasks. Among them, squatting is an important position.

AIM

To provide a new squat position classification and evaluate the different squatting positions of a series of patients after primary TKA.

METHODS

From May 2018 to October 2019, we retrospectively reviewed 154 video recordings of the squatting-related motions of patients after TKA. Among the included patients, 119 were women and 35 were men. Their mean age at the index surgery was 61.4 years (range, 30 to 77).

RESULTS

The median follow-up was 12 mo (range, 6 to 156 mo). We classified those squatting-related motions into three major variations according to squatting depth: Half squat, parallel squat, and deep squat. The angles of hip flexion, knee flexion, and ankle dorsiflexion were measured in the screenshots captured from the videos at the moment of squatting nadir. A total of 26 patients were classified as half squats, 75 as parallel squats, and 53 as deep squats. The angles of hip flexion, knee flexion, and ankle dorsiflexion all differed significantly among the three squatting positions (P < 0.001). In the parallel squat group, the mean knee flexion angle (°) was 116.5 (SD, 8.1; range, 97 to 137). In the deep squat group, the mean knee flexion angle (°) was 132.5 (SD, 9.3; range, 116 to 158).

CONCLUSION

Among the three squatting positions, deep squat showed the highest hip, knee, and ankle flexion angles, followed by the parallel squat. With the improvement of squatting ability, the patient's postoperative satisfaction rate was also significantly enhanced. However, the different squatting abilities of the patients cannot be effectively distinguished from the scoring results (P > 0.05). Our squatting position classification offers a pragmatic approach to evaluating patients’ squatting ability after TKA.

Bar Load-Velocity Profile of Full Squat and Bench Press Exercises in Young Recreational Athletes

The purpose of this study was to determine the mean propulsive velocity (MVP) at various percentages of one repetition maximum (1RM) in the full squat and chest press exercises. A total of 96 young women and 256 young men (recreational athletes) performed an incremental test (50−60−70−80% 1RM) comprising the bench press and full squat exercises in two different sessions. The individual load and velocity ratios were established through the MPV. Data were analyzed using SPSS software version 25.0, with the significance level set at 5%. The following findings were revealed: highly linear load-velocity relationships in the group of women (r = 0.806 in the squat, and r = 0.872 in the bench press) and in the group of men (r = 0.832 and r = 0.880, respectively); significant differences (p < 0.001) in the MPV at 50−70−80% 1RM between the bench press and the full squat in men and at 70−80% 1RM in women; and a high variability in the MPV (11.49% to 22.63) in the bench press and full squat (11.58% to 25.15%) was observed in women and men (11.31% to 21.06%, and 9.26% to 24.2%) at the different percentages of 1RM evaluated. These results suggest that the load-velocity ratio in non-strength-trained subjects should be determined individually to more precisely establish the relative load to be used in a full squat and bench press training program.

Maximal strength training in patients with inflammatory rheumatic disease: implications for physical function and quality of life

PURPOSE

Patients with inflammatory rheumatic disease (IRD) have attenuated muscle strength in the lower extremities, resulting in impaired physical function and quality of life. Although maximal strength training (MST), applying heavy resistance, is documented to be a potent countermeasure for such attenuation, it is uncertain if it is feasible in IRD given the pain, stiffness, and joint swelling that characterize the population.

METHODS

23 patients with IRD (49 ± 13 years; 20 females/3 males), diagnosed with spondyloarthritis, rheumatoid arthritis, or systemic lupus erythematosus, were randomized to MST or a control group (CG). The MST group performed four × four repetitions dynamic leg press two times per week for 10 weeks at ~ 90% of one repetition maximum (1RM). Before and after training 1RM, rate of force development (RFD), and health-related quality of life (HRQoL) were measured.

RESULTS

Session attendance in the MST group was 95%, of which 95% conducted according to MST protocol. Furthermore, MST increased 1RM (29 ± 12%, p = 0.001) and early and late phase RFD (33-76%, p < 0.05). All improvements were different from the CG (p < 0.05). MST also resulted in HRQoL improvements in the dimensions; physical functioning, general health, and vitality (p < 0.05). Physical functioning was associated with 1RM (rho = 0.55, p < 0.01) and early phase RFD (rho = 0.53-0.71, p < 0.01; different from CG p < 0.05).

CONCLUSIONS

Despite being characterized by pain, stiffness, and joint swelling, patients with IRD appear to tolerate MST well. Given the improvements in 1RM, RFD, and HRQoL MST should be considered as a treatment strategy to counteract attenuated muscle strength, physical function, and HRQoL.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04998955, retrospectively registered.

An EMG-Based Constitutive Law for Force Generation in Skeletal Muscle - Part II: Model Validation On the Ankle Joint Complex

This study evaluates the predictive ability of the skeletal muscle force model derived previously within the ankle joint complex. The model is founded in dimensional analysis, using electromyography and the muscle force-length, force-velocity, and force-frequency curves as inputs. Seventeen subjects (8 males, 9 females) performed five different exercises that activated the primary muscles crossing the ankle joint. Motion capture, force plate, and electromyography data were collected during these exercises. A constant, Km, was calculated for each muscle of each subject using four of the five exercises. The fifth exercise was used to validate the results by treating the moments due to muscle forces as known and all other components in Euler's second law as unknown. While muscle forces cannot be directly validated in vivo, methods can be developed to test these values with reasonable confidence. This study compared moments about the ankle joint due to the calculated muscle forces to the sum of the moments due to all other sources and the kinematic terms in the second Newton-Euler equation of rigid body motion. Average percent errors for each subject ranged from 4.2% to 15.5% with an average percent error across all subjects of 8.2% while maximum percent errors for each subject ranged from 33.3% to 78.0% with an overall average maximum of 52.4%. Future work will examine sensitivity analyses to identify potential simplifications to the model and solution process and will validate the model on a more complex joint.

Injury in CrossFit®: A Systematic Review of Epidemiology and Risk Factors

OBJECTIVE

To review the characteristics of the injuries among CrossFit® practitioners, including prevalence and incidence, nature, location, and risk factors.

METHODS

PubMed/MEDLINE, EMBASE, Web of Science, Scopus, and SPORTDiscus databases were searched from inception through August 2020, and English-language articles reporting on CrossFit®-related injuries were included. Data including sample (sex, age, and demographics) and injuries' characteristics (prevalence, incidence rate, nature, location, percentage of injuries requiring surgery and risk factors) were extracted.

RESULTS

Overall, twenty-five studies involving a total of 12,079 CrossFit® practitioners met the inclusion criteria. The mean prevalence of injuries among the included studies was 35.3%, with an incidence rate varying between 0.2 and 18.9 per 1000 hours of training. The most injured areas were shoulder (26%), spine (24%), and knee (18%). Among the studies that reported the injuries requiring surgery, the mean percentage was 8.7%. Regarding the risk factors associated with injuries, older age, male sex, a greater body mass index, the existence of previous injuries, the lack of coach supervision, the experience on CrossFit® and the participation in competitions were reported by the studies.

CONCLUSIONS

CrossFit® training has an injury incidence rate similar to weightlifting and powerlifting. Findings from the studies suggest that the most affected areas are shoulder, spine, and knee. The limited quality of the studies prevents us from drawing solid conclusions about injury risk factors.

Variation characteristics of stress distribution in the subchondral bone of the knee joint of judo athletes with long-term stress changes

OBJECTIVE

To investigate the distribution of bone density in the subchondral bone tissue of the knee joint due to the mechanical stress load generated by judo, the bone tissue volume of different densities and the bone remodeling characteristics of the subchondral bone of the knee joint.

METHODS

CT imaging data of the knee joint were collected from 15 healthy individuals as controls and 15 elite judo athletes. Firstly, they were processed by the CTOAM technique, and secondly, the distribution pattern of high-density areas of the knee joint was localized using nine anatomical regions. In addition, three tomographic images were selected in the sagittal, coronal, and axial 2D image windows to observe the distribution of different densities of bone tissue. Finally, the percentage of bone tissue volume (%BTV) and bone remodeling trend of bone tissues with different densities were determined.

RESULTS

In this study, high-density areas were found in the 4th, 5th, and 6th regions of the articular surface of the distal femur and the 1st, 2nd, 3rd, 4th, 5th, 6th, 7th and 8th regions of the tibial plateau in judo athletes; the distribution of high-density areas on the articular surface of the distal femur in control subjects was similar with judo athletes, and high-density areas were mainly found in the 4th and 5th regions of the tibial plateau. The %BTV of low (401-500HU in the distal femur; 301-400 HU and 401-500HU in the tibial plateau), moderate, and high bone density was higher in judo athletes than in controls in the subchondral bone of the distal femur and tibial plateau (P< 0.05).

CONCLUSION

The history of compressive stresses, struck stresses, soft tissue tension and pull, self-gravity and intra-articular stress loading generated by the lower limb exercise technique of judo leads to specific forms of stress distribution and bone tissue remodeling in the subchondral bone tissue within the distal femur and tibia plateau.

Sagittal spine disposition and pelvic tilt during outdoor fitness equipment use and their associations with kinanthropometry proportions in middle-aged and older adults

BACKGROUND

Outdoor fitness training has become popular as a tool for improving the health, especially middle-aged and older adults. For this purpose, outdoor fitness equipment (OFE) have been installed in public areas. However, their safety and effectiveness are still unknown. The aim of the present research was to analyze the sagittal disposition of the spine and pelvic tilt during the use of OFE, and to determine the influence of anthropometric variables on these factors in middle-aged and older adults.

METHODS

Seventy healthy volunteers, 56 women and 14 men (age: 63.14 ± 8.19 years) participated in the study. Sagittal spine disposition and pelvic tilt were measured using a Spinal Mouse®, in the relaxed standing position, and during the use of the OFE. In addition, kinanthropometry variables were also measured according to the guidelines of the International Society for the Advancement of Kinanthropometry.

RESULTS

Regarding thoracic kyphosis, a significant decrease was found in thoracic kyphosis in the initial position (IP) in single bonny rider (SBR) (p = 0.006) and row (p = 0.046), and a significant increase in the final position (FP) in the row (p = 0.011), surfboard (p < 0.001) and air walker (p = 0.027) machines. In relation to the lumbar curvature and pelvic tilt, a significant decrease in lumbar lordosis and a decrease in pelvic anteversion were observed in the IP and FP in SBR and row; and in the bike (p < 0.001) machine. In the surfboard machine, a significant decrease in lumbar lordosis was found (p = 0.002), with no changes in pelvic tilt. According to the multiple linear regression analysis, the subjects with a higher cormic index and height were more at risk of increasing their thoracic kyphosis, decreasing lumbar lordosis and/or decreasing pelvic anteversion towards pelvic retroversion.

CONCLUSIONS

Middle-aged and older adults show spinal misalignments when using the OFE with respect to the standing position, showing a decrease in the thoracic kyphosis in IP of SBR and ROW, and a significant increase in the surfboard and air walker, and in the FP of Row, in the lumbar lordosis in all the OFE in sitting and some in standing, and in the pelvic anteversion in all the OFE in sitting. The variables height and the cormic index explained most of the changes in sagittal spine disposition.

Factors Affecting Squatting Ability in Total Knee Arthroplasty Using High Flexion Prosthesis

Purpose

Total knee arthroplasty (TKA) is widely used as a treatment for knee osteoarthritis. Few studies have analysed the factors affecting the squatting ability of patients after TKA. The purpose of this study was to comprehensively analyse the factors affecting squatting ability after TKA and to determine which ones are important.

Patients and Methods

Three hundred primary TKA cases with a minimum 3-year follow-up were retrospectively analysed. All patients received a conventional posterior-stabilized TKA implant and underwent a standard perioperative care pathway. The patients were divided into two groups according to the squatting position and knee flexion angle while weight-bearing (Group I – inability to squat group, Group II – ability to squat group). Demographic, operative, and clinical data were collected. Radiographic assessment included joint line elevation, patellar position, posterior condylar offset (PCO), etc. Statistical analysis of the effect of all the above factors on squatting ability was performed.

Results

The preoperative range of motion and joint line of Group I were 82.9±12.6 and 3.24±1.07, respectively, and those of Group II were 107±9.6 and 1.83±0.89 respectively. The univariate analysis showed that age, prosthesis size, preoperative ROM and joint line position were correlated with squatting ability. But in the final multivariate analysis, joint line position and preoperative ROM were independent influencing factors that affected squatting ability after TKA (p value < 0.01).

Conclusion

Preoperative ROM and joint line position were independent influencing factors affecting squatting ability after TKA. Patients should be counseled accordingly and be made to understand these factors. To ensure that patients can squat postoperatively, we should improve surgical techniques to control joint line elevation.

Novice Female Exercisers Exhibited Different Biomechanical Loading Profiles during Full-Squat and Half-Squat Practice

Simple Summary

This study adapted a customized OpenSim model aiming to analyze the loadings difference between full-squat and half-squat in novice females. The joint moment and joint angle of the hip, knee, and ankle increase significantly in the full-squat, which might increase the risks of potential injury. In the case of training, the cohort of young females could perform half-squat practice when muscle strength is insufficient. This study may present implications for the design of novice strength training programs and the formulation of rehabilitation plans.

Abstract

Background: Females with different practice experience may show different body postures and movement patterns while squatting in different depths, which may lead to changes of biomechanical loadings and increase the risks of injuries. Methods: Sixteen novice female participants without squat training experience participated in this study. A 3D motion capture system was used to collect the marker trajectory and ground reaction force data during bodyweight squatting in different depths. The participants’ kinematic data and joint moment were calculated using OpenSim’s inverse kinematics and inverse dynamics algorithm. In this study, authors adapted a model especially developed for squatting and customized the knee joint with extra Degree-of-Freedom (DoF) in the coronal and horizontal plane with adduction/abduction and internal/external rotation. A paired-sample t-test was used to analyze the difference of joint range of motions (ROM) and peak moments between full-squat (F-SQ) and half-squat (H-SQ). One-Dimensional Statistical Parametric Mapping (SPM1D) is used to analyze the difference of joint angle and moment between the process of squatting F-SQ and H-SQ. Results: (1) Compared with H-SQ, F-SQ showed larger ROM in sagittal, coronal, and transverse planes (p < 0.05). (2) SPM1D found that the difference in joint angles and joint moments between F-SQ and H-SQ was mainly concentrated in the mid-stance during squatting, which suggested the difference is greatly pronounced during deeper squat. (3) Peak hip extension moment, knee extension moment, hip adduction moment, and plantar flexion moment of F-SQ were significantly higher than H-SQ (p < 0.05). (4) Difference of hip and knee extension moments and rotation moments between the F-SQ and H-SQ were exhibited during descending and ascending. Conclusions: The study found that novice women had larger range of joint motion during the F-SQ than H-SQ group, and knee valgus was observed during squatting to the deepest point. Greater joint moment was found during F-SQ and reached a peak during ascending after squatting to the deepest point. Novice women may have better movement control during H-SQ. The findings may provide implications for the selection of lower limb strength training programs, assist the scientific development of training movements, and provide reference for squat movement correction, thus reducing the risk of injury for novice women in squatting practice.

Association of markers of patellofemoral maltracking to cartilage damage and bone marrow lesions on MRI: Data from the 2016 Olympic Games of Rio De Janeiro

Background

Patellofemoral joint (PFJ) disease is a common ailment in elite athletes. Our aim is to report the frequency of superolateral Hoffa’s fat pad (SHFP) edema, and PFJ cartilage damage and bone marrow lesions (BML), among Olympian athletes, and to study the association between measurements of trochlear morphology and vertical patellar position and a) PFJ cartilage damage or BML, and b) SHFP edema.

Methods

All knee MRI, performed in the Olympic Village and polyclinics, of participating athletes in the 2016 Olympic Games of Rio de Janeiro were included. MRI were scored for PFJ cartilage damage and BML, and SHFP edema. Trochlear morphology measurements included sulcus angle, trochlear angle, lateral trochlear inclination, and medial trochlear inclination. Insall-Salvati ratio was also assessed.

Results

One hundred twenty-one knee MRIs were included (62 female, 51.2 %). The highest frequencies of PFJ cartilage damage, combination of PFJ cartilage damage and BML, and SHFP edema were found among Beach Volleyball and Volleyball athletes. SHFP edema was more common among female compared to male Olympian athletes. We found no statistically significant associations between different measurements of trochlear morphology/vertical patellar position, and 1. SHFP edema, and 2. PFJ cartilage damage/BML.

Conclusion

SHFP edema and the combination of PFJ cartilage damage and BML are highly frequent among Olympic athletes especially those competing in Beach volleyball and Volleyball. SHFP edema is more common among female athletes. Further studies are needed to determine whether PFJ cartilage damage has a stronger association to sports disciplines rather than trochlear morphology.

Comparison of Joint and Muscle Biomechanics in Maximal Flywheel Squat and Leg Press

The aim was to compare the musculoskeletal load distribution and muscle activity in two types of maximal flywheel leg-extension resistance exercises: horizontal leg press, during which the entire load is external, and squat, during which part of the load comprises the body weight. Nine healthy adult habitually strength-training individuals were investigated. Motion analysis and inverse dynamics-based musculoskeletal modelling were used to compute joint loads, muscle forces, and muscle activities. Total exercise load (resultant ground reaction force; rGRF) and the knee-extension net joint moment (NJM) were slightly and considerably greater, respectively, in squat than in leg press (p ≤ 0.04), whereas the hip-extension NJM was moderately greater in leg press than in squat (p = 0.03). Leg press was performed at 11° deeper knee-flexion angle than squat (p = 0.01). Quadriceps muscle activity was similar in squat and leg press. Both exercise modalities showed slightly to moderately greater force in the vastii muscles during the eccentric than concentric phase of a repetition (p ≤ 0.05), indicating eccentric overload. That the quadriceps muscle activity was similar in squat and leg press, while rGRF and NJM about the knee were greater in squat than leg press, may, together with the finding of a propensity to perform leg press at deeper knee angle than squat, suggest that leg press is the preferable leg-extension resistance exercise, both from a training efficacy and injury risk perspective.

Effects of range of motion on resistance training adaptations: A systematic review and meta-analysis

BACKGROUND

Nowadays, there is a lack of consensus and high controversy about the most effective range of motion (ROM) to minimize the risk of injury and maximize the resistance training adaptations.

OBJECTIVE

To conduct a systematic review and meta-analysis of the scientific evidence examining the effects of full and partial ROM resistance training interventions on neuromuscular, functional, and structural adaptations.

METHODS

The original protocol (CRD42020160976) was prospectively registered in the PROSPERO database. Medline, Scopus, and Web of Science databases were searched to identify relevant articles from the earliest record up to and including March 2021. The RoB 2 and GRADE tools were used to judge the level of bias and quality of evidence. Meta-analyses were performed using robust variance estimation with small-sample corrections.

RESULTS

Sixteen studies were finally included in the systematic review and meta-analyses. Full ROM training produced significantly greater adaptations than partial ROM on muscle strength (ES = 0.56, p = 0.004) and lower-limb hypertrophy (ES = 0.88, p = 0.027). Furthermore, although not statistically significant, changes in functional performance were maximized by the full ROM training (ES = 0.44, p = 0.186). Finally, no significant superiority of either ROM was found to produce changes in muscle thickness, pennation angle, and fascicle length (ES = 0.28, p = 0.226).

CONCLUSION

Full ROM resistance training is more effective than partial ROM to maximize muscle strength and lower-limb muscle hypertrophy. Likewise, functional performance appears to be favored by the use of full ROM exercises. On the contrary, there are no large differences between the full and partial ROM interventions to generate changes in muscle architecture.

How accurate are visual assessments by physical therapists of lumbo-pelvic movements during the squat and deadlift?

OBJECTIVES

To investigate the accuracy of visual assessments made by physical therapists of lumbo-pelvic movements during the squat and deadlift and how much movement is considered injurious.

DESIGN

Quantitative Cross-sectional.

PARTICIPANTS

14 powerlifters, 10 Olympic weightlifters and six physical therapists.

SETTING

The lifters were recorded simultaneously by video and an inertial measurement unit (IMU) system while performing squats and deadlifts. The physical therapists assessed the videos and rated whether specific lumbo-pelvic movements were visible during the lifts and whether the movement amplitude was considered injurious.

MAIN OUTCOME MEASURES

The nominal visual assessments, if there was a movement and if it was considered injurious, were compared to the degrees of movement attained from the IMU system.

RESULTS

During the squat, a posterior pelvic tilt of ≥34° was required to visually detect the movement. For other lumbo-pelvic movements, there was no significant difference in the amount of movement between those who were assessed as moving or not moving their lumbo-pelvic area, nor was there a difference in movement amplitude between those who were assessed as having an increased risk of injury or not.

CONCLUSIONS

Physical therapists did not consistently detect lumbo-pelvic movements during squats and deadlifts when performed by competitive lifters.

Assessment of Back-Squat Performance at Submaximal Loads: Is the Reliability Affected by the Variable, Exercise Technique, or Repetition Criterion?

This study aimed to compare the between-session reliability of different performance variables during 2 variants of the Smith machine back-squat exercise. Twenty-six male wrestlers performed 5 testing sessions (a 1-repetition maximum [1RM] session, and 4 experimental sessions [2 with the pause and 2 with the rebound technique]). Each experimental session consisted of performing 3 repetitions against 5 loads (45-55-65-75-85% of the 1RM). Mean velocity (MV), mean power (MP), peak velocity (PV), and peak power (PP) variables were recorded by a linear position transducer (GymAware PowerTool). The best and average scores of the 3 repetitions were considered for statistical analyses. The coefficient of variation (CV) ranged from 3.89% (best PV score at 55% 1 RM using the pause technique) to 10.29% (average PP score at 85% 1 RM using the rebound technique). PP showed a lower reliability than MV, MP, and PV (CV_ratio ≥ 1.26). The reliability was comparable between the exercise techniques (CV_ratio = 1.08) and between the best and average scores (CV_ratio = 1.04). These results discourage the use of PP to assess back-squat performance at submaximal loads. The remaining variables (MV, MP, or PV), exercise techniques (pause or rebound), and repetition criteria (best score or average score) can be indistinctly used due to their acceptable and comparable reliability.

Lower limb muscle and joint forces during front and back squats performed on a Smith machine

BACKGROUND: Comparison of knee loads on a Smith machine, which is utilised for maintenance of health and rehabilitation, has not been attempted. OBJECTIVE: This study compared lower limb muscle and knee joint forces during front and back squats performed on a Smith Machine. METHODS: Eleven participants performed front and back squats with loads at 40%, 60% and 80% of their back squat 1-RMs. Ground reaction forces and three-dimensional full body motion were collected and used for modelling lower limb muscle and knee joint forces. RESULTS: Larger loads increased tibiofemoral compressive force during back squat at 80% compared to 40% (p< 0.01; d= 1.58) and to 60% (p< 0.01; d= 1.37). Patellofemoral compressive (p= 0.96) and tibiofemoral shear forces (p= 0.55) were not influenced by external load or type of squat. Gluteus medius and minimus produced more force at 80% compared to 60% (p= 0.01; d= 1.10) and to 40% (p< 0.01; d= 1.87) without differences for other muscles (p= 0.09–0.91). CONCLUSIONS: Greater external load was associated with increase in gluteus medius and minimus force and with increased tibiofemoral compressive force without effects on tibiofemoral shear force, patellofemoral compressive force or other lower limb muscle forces.

Selection of Resistance Exercises for Older Individuals: The Forgotten Variable

Resistance training has been widely recommended as a strategy to enhance the functional autonomy and quality of life in older individuals. Among the variables that comprise a training session, the selection of exercises stands out as an important consideration for the elderly. Although a wide range of resistance exercise options exists, current guidelines generally do not indicate which exercises should be included and which muscles should be prioritized when prescribing training for older individuals. Therefore, given the lack of evidence-based information on the topic, this paper endeavors to establish recommendations to help guide the prescription of resistance exercises for older adults.

Relationship Between Maximal Dynamic Force in the Deep Back Squat and Sprinting Performance in Consecutive Segments Up to 30 m

ABSTRACT

Möck, S, Hartmann, R, Wirth, K, Rosenkranz, G, and Mickel, C. Relationship between maximal dynamic force in the deep back squat and sprinting performance in consecutive segments up to 30 m. J Strength Cond Res 35(4): 1039-1043, 2021-The sprint (in track and field athletics) is characterized by a fluent transition from predominantly knee extending musculature during the initial acceleration phase toward dominance of the hamstring muscle group thereafter. Because of this change in technique, it can be assumed that there is a decrease of correlation of the maximal dynamic force of the deep back squat and sprinting performance with increasing distance. Therefore, sprinting performance for consecutive intervals (0-5, 5-10, 10-15, 15-20, 20-25, and 25-30 m) as well as the 1 repetition maximum (1RM) were determined. Our results show statistically significant (p < 0.01) correlations for both the relationships with the absolute 1RM (r = -0.614 to -0.808) and the relative 1RM (r = -0.646 to -0.749). However, the expected decrease in correlation over distance was not found. The results show that the maximal dynamic force of hip and knee extensors are a basic performance requirement in short-distance sprinting and should be considered in training recommendations.

Jumping with barbell load: Assessment of lower limb joint kinematics and kinetics during landing

Loaded jumps are commonly used to improve leg muscle power. However, the additional load during jump-landing might increase the potential for overuse injury. Therefore, the aims of this study were to evaluate the effect that barbell load has on lower limb joint kinematics and kinetics during jump-landing and to evaluate the effect of arresting the barbell load at flight apex prior to landing on joint kinematic and kinetic variables. Barbell-loaded squat jumps (20, 40, and 60 kg) were investigated during two jump-landing conditions: 1) barbell-loaded (landing with barbell load) and 2) barbell-arrested (barbell load arrested at flight apex prior to jump-landing). Lower body kinematics and joint kinetics were assessed during jump-landing. In the barbell-loaded jump-landing condition, joint angles at initial contact decreased with increasing barbell load. Knee and hip peak power decreased (knee: -38%; hip: -46%), while ankle joint work increased with increasing barbell load. Joint moments, powers and work were decreased in the barbell-arrested condition compared to the barbell-loaded condition. Barbell-loaded jump-landings do not pose increased demands on the knee and the hip joint compared to bodyweight only jump-landings, due to the load-based reductions in jump height and joint kinematic adaptions. However, ankle joint contribution in energy dissipation is increased, possibly resulting in an increased overuse injury risk at this joint. Arresting the barbell load at flight apex prior to jump-landing substantially reduces the joint kinetics, hence serving as valuable training tool for athletes returning to sport after injuries.

Effect of Pause Versus Rebound Techniques on Neuromuscular and Functional Performance After a Prolonged Velocity-Based Training

PURPOSE

A variation of the traditional squat (SQ) rebound technique (REBOUND) including a momentary pause ∼2 seconds (PAUSE) between eccentric and concentric phases has been proposed. Although there is a consensus about the lower acute effects on performance of this PAUSE variant compared with traditional REBOUND technique, no information exists about the differences in longitudinal adaptations of these SQ executions.

METHODS

A total of 26 men were randomly assigned into the PAUSE (n = 13) or REBOUND (n = 13) groups and completed a 10-week velocity-based training using the SQ exercise, only differing in the technique. Neuromuscular adaptations were assessed by the changes in the 1-repetition maximum strength and mean propulsive velocity achieved against the absolute loads (in kilograms) common to pretest and posttest. Functional performance was evaluated by the following tests: countermovement jump, Wingate, and sprint time at 0 to 10, 10 to 20, and 0 to 20 m.

RESULTS

Whereas both groups showed significant increases in most of the neuromuscular tests (P < .05), the PAUSE (effect size [ES] = 0.76-1.12) presented greater enhancements than REBOUND (ES = 0.45-0.92). Although not significant, improvements in Wingate and sprint time at 0 to 10 and 0 to 20 m were higher for PAUSE (ES = 0.31-0.46) compared with REBOUND (ES = 0.10-0.29). Conversely, changes on countermovement jump and sprint time at 10 to 20 m were superior for REBOUND (ES = 0.17-0.88) than for PAUSE (ES = 0.09-0.75).

CONCLUSION

Imposing a pause between eccentric and concentric phases in the SQ exercise could be an interesting strategy to increase neuromuscular and functional adaptations in sport actions that mainly depend on concentric contractions. Moreover, sport abilities highly dependent on the stretch-shortening cycle could benefit from the REBOUND or a combination of the 2 techniques.

Vibroarthrographic analysis of patellofemoral joint arthrokinematics during squats with increasing external loads

Background

The patellofemoral joint (PFJ) provides extremely low kinetic friction, which results in optimal arthrokinematic motion quality. Previous research showed that these friction-reducing properties may be diminished due to the increase in articular contact forces. However, this phenomenon has not been analyzed in vivo during functional daily-living activities. The aim of this study was the vibroarthrographic assessment of changes in PFJ arthrokinematics during squats with variated loads.

Methods

114 knees from 57 asymptomatic subjects (23 females and 34 males) whose ages ranged from 19 to 26 years were enrolled in this study. Participants were asked to perform 3 trials: 4 repetitions of bodyweight squats (L0), 4 repetitions of 10 kg barbell back loaded squats (L10), 4 repetitions of 20 kg barbell back loaded squats (L20). During the unloaded and loaded (L10, L20) squats, vibroarthrographic signals were collected using an accelerometer placed on the patella and were described by the following parameters: variation of mean square (VMS), mean range (R4), and power spectral density for frequency of 50–250 Hz (P1) and 250–450 Hz (P2).

Results

Obtained results showed that the lowest values were noted in the unloaded condition and that the increased applied loads had a significant concomitant increase in all the aforementioned parameters bilaterally (p < 0.05).

Conclusion

This phenomenon indicates that the application of increasing knee loads during squats corresponds to higher intensity of vibroacoustic emission, which might be related to higher contact stress and kinetic friction as well as diminished arthrokinematic motion quality.

Patellofemoral joint kinetics in females when using different depths and loads during the barbell back squat

Back squats are a common strengthening exercise for knee and hip musculature. However, repetitive loaded movements like backs squats result in high patellofemoral joint loading and therefore may contribute to the development of common overuse injuries. Thus, it is important to understand how changing parameters such as squat depth or load influences patellofemoral loading. This study investigated differences in patellofemoral loading when experienced female lifters squatted to three depths (above parallel, parallel, and below parallel) and with three loads (unloaded, 50%, and 85% of depth-specific one repetition maximums). Patellofemoral joint reaction forces (pfJRF) and stresses (pfJS) were calculated from biomechanical models incorporating knee extensor moments (KEM) and joint angles. Peak KEMs displayed a depth-by-load interaction such that within each depth, as load increased so did peak KEM. However, within each load, the effects of depth were different. Peak pfJRF also increased with load and was higher at below parallel than above or parallel depths. Peak pfJS also displayed a depth-by-load interaction, increasing with load within a given depth, and being greatest at the below parallel depths within a given load. If patellofemoral joint loading is a concern, clinicians or coaches should carefully monitor the depth and load combinations being used.

A Comparison Between the Squat and the Deadlift for Lower Body Strength and Power Training

The aim of this study was to compare the effects of two resistance training programs including either a deadlift or a parallel squat on lower body maximal strength and power in resistance trained males. Twenty-five resistance trained men were randomly assigned to a deadlift group (DE; n = 14; age = 24.3 ± 4.1 y; body mass = 84.8 ± 14.2 kg; body height = 180.3 ± 6.8 cm) or to a squat group (SQ; n = 11; age = 22.3 ± 1.6 y; body mass = 83.0 ± 13.6 kg; body height 179.9 ± 6.1 cm). Both groups trained 3 times per week for 6 weeks. The deadlift and the squat were the only lower body maximal strength exercises performed by DE and SQ groups, respectively, while both training programs included jumps. A significantly (p = 0.017) greater increase in deadlift 1RM was observed in the DE compared to the SQ group, while the SQ group obtained a significantly (p = 0.049) greater increase in squat 1RM. A significant increase in jump performance (p = 0.010), without significant interactions between groups (p = 0.552), was observed in both groups. Three participants of the DE group developed lower back pain and were excluded from the study. Results indicate that both the squat and the deadlift can result in similar improvement in lower body maximal strength and jump performance and can be successfully included in strength training programs. The incidence of back pain in the DE group may suggest a marked stress of this exercise on the lower back. Proper technique should be used to minimize the risk of injury, especially when the deadlift is performed.

A Novel Strategy to Determine the 1-Repetition Maximum in the Jump Squat Exercise

Loturco, I, McGuigan, MR, Rodríguez-Rosell, D, Pereira, LA, and Pareja-Blanco, F. A novel strategy to determine the 1-repetition maximum in the jump squat exercise. J Strength Cond Res XX(X): 000-000, 2020-This study aimed to determine the maximum relative load of the half-squat (HS; i.e., % HS 1-repetition maximum [1RM]) that can be used in its ballistic variation, namely, the jump squat (JS) exercise, and to examine whether this reference value varies in subjects with different strength levels. In total, 186 elite athletes from 10 distinct sport disciplines participated in this study. A progressive loading test up to HS 1RM was performed during the competitive phase of the season for all athletes. Mean propulsive velocity and propulsive phase duration were also assessed during the 1RM test. Athletes were divided into 3 distinct subgroups: "low," "middle," and "high" strength levels, based on their relative HS 1RM values (kg·kg). A 1-way analysis of variance was used to compare the variables assessed between the groups. Significance level was set at p < 0.05. The high group demonstrated the highest relative HS 1RM values, followed by the middle and low groups (all p < 0.05). No significant differences were observed between the groups for the remaining variables (p > 0.05). It was observed that at 86.0 ± 5.4% 1RM, the full concentric action can already be considered as entirely propulsive in the HS exercise for all subjects, independent of their strength levels. Therefore, this relative strength value may be used as a reference for the 1RM in the JS exercise.

Effects of 120 vs. 60 and 90 g/h Carbohydrate Intake during a Trail Marathon on Neuromuscular Function and High Intensity Run Capacity Recovery

BACKGROUND

Current carbohydrate (CHO) intake recommendations for ultra-trail activities lasting more than 2.5 h is 90 g/h. However, the benefits of ingesting 120 g/h during a mountain marathon in terms of post-exercise muscle damage have been recently demonstrated. Therefore, the aim of this study was to analyze and compare the effects of 120 g/h CHO intake with the recommendations (90 g/h) and the usual intake for ultra-endurance athletes (60 g/h) during a mountain marathon on internal exercise load, and post-exercise neuromuscular function and recovery of high intensity run capacity.

METHODS

Twenty-six elite trail-runners were randomly distributed into three groups: LOW (60 g/h), MED (90 g/h) and HIGH (120 g/h), according to CHO intake during a 4000-m cumulative slope mountain marathon. Runners were measured using the Abalakov Jump test, a maximum a half-squat test and an aerobic power-capacity test at baseline (T1) and 24 h after completing the race (T2).

RESULTS

Changes in Abalakov jump time (ABKJT), Abalakov jump height (ABKH), half-squat test 1 repetition maximum (HST1RM) between T1 and T2 showed significant differences by Wilcoxon signed rank test only in LOW and MED (p < 0.05), but not in the HIGH group (p > 0.05). Internal load was significantly lower in the HIGH group (p = 0.017) regarding LOW and MED by Mann Whitney u test. A significantly lower change during the study in ABKJT (p = 0.038), ABKH (p = 0.038) HST1RM (p = 0.041) and in terms of fatigue (p = 0.018) and lactate (p = 0.012) within the aerobic power-capacity test was presented in HIGH relative to LOW and MED.

CONCLUSIONS

120 g/h CHO intake during a mountain marathon might limit neuromuscular fatigue and improve recovery of high intensity run capacity 24 h after a physiologically challenging event when compared to 90 g/h and 60 g/h.

A Comparative Study on Loadings of the Lower Extremity during Deep Squat in Asian and Caucasian Individuals via OpenSim Musculoskeletal Modelling

Populations of different ethnicities may present different movement capacities and muscular function adaptations. The purpose of this study was to investigate the differences of motion and loading in the lower extremity during dynamic deep squats between Asian and Caucasian individuals using OpenSim modelling technique with a customized squat-specific musculoskeletal model. Twenty-four participants joined the test performing the step-squat test, with right foot stepping side, squatting, and returning. The one-dimensional statistical parametric mapping package was used for statistical analysis. The main findings of the current study were as follows: (1) significant lower squat depth was observed in the Asian individuals, (2) the greater knee range of motion and contact forces were found in the Asian individuals, and (3) the greater ankle contact forces in the Caucasian individuals were notable while performing the deep squat compared to the Asian group. Knowledge found in the current study may provide implication for exercise practitioners and physiotherapists while designing schemes for the prevention of loading accumulation in the lower extremity.

Influence of gravity on biomechanics in flywheel squat and leg press

Resistance exercise on Earth commonly involves both body weight and external load. When developing exercise routines and devices for use in space, the absence of body weight is not always adequately considered. This study compared musculoskeletal load distribution during two flywheel resistance knee-extension exercises, performed in the direction of (vertical squat; S) or perpendicular to (horizontal leg press; LP) the gravity vector. Eleven participants performed these two exercises at a given submaximal load. Motion analysis and musculoskeletal modelling were used to compute joint loads and to simulate a weightless situation. The flywheel load was more than twice as high in LP as in S (p < 0.001). Joint moments and forces were greater during LP than during S in the ankle, hip and lower back (p < 0.01) but were similar in the knee. In the simulated weightless situation, hip and lower-back loadings in S were higher than corresponding values at Earth gravity (p ≤ 0.01), whereas LP joint loads did not increase. The results suggest that LP is a better terrestrial analogue than S for knee-extension exercise in weightlessness and that the magnitude and direction of gravity during resistance exercise should be considered when designing and evaluating countermeasure exercise routines and devices for space.

Statistical Modeling of Lower Limb Kinetics During Deep Squat and Forward Lunge

Purpose

Modern statistics and higher computational power have opened novel possibilities to complex data analysis. While gait has been the utmost described motion in quantitative human motion analysis, descriptions of more challenging movements like the squat or lunge are currently lacking in the literature. The hip and knee joints are exposed to high forces and cause high morbidity and costs. Pre-surgical kinetic data acquisition on a patient-specific anatomy is also scarce in the literature. Studying the normal inter-patient kinetic variability may lead to other comparable studies to initiate more personalized therapies within the orthopedics.

Methods

Trials are performed by 50 healthy young males who were not overweight and approximately of the same age and activity level. Spatial marker trajectories and ground reaction force registrations are imported into the Anybody Modeling System based on subject-specific geometry and the state-of-the-art TLEM 2.0 dataset. Hip and knee joint reaction forces were obtained by a simulation with an inverse dynamics approach. With these forces, a statistical model that accounts for inter-subject variability was created. For this, we applied a principal component analysis in order to enable variance decomposition. This way, noise can be rejected and we still contemplate all waveform data, instead of using deduced spatiotemporal parameters like peak flexion or stride length as done in many gait analyses. In addition, this current paper is, to the authors’ knowledge, the first to investigate the generalization of a kinetic model data toward the population.

Results

Average knee reaction forces range up to 7.16 times body weight for the forwarded leg during lunge. Conversely, during squat, the load is evenly distributed. For both motions, a reliable and compact statistical model was created. In the lunge model, the first 12 modes accounts for 95.26% of inter-individual population variance. For the maximal-depth squat, this was 95.69% for the first 14 modes. Model accuracies will increase when including more principal components.

Conclusion

Our model design was proved to be compact, accurate, and reliable. For models aimed at populations covering descriptive studies, the sample size must be at least 50.