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

Lower Serum Creatinine Is a New Risk Factor of Type 2 Diabetes: The Kansai Healthcare Study

OBJECTIVE—Because skeletal muscle is one of the target tissues for insulin, skeletal muscle mass might be associated with type 2 diabetes. Serum creatinine is a possible surrogate marker of skeletal muscle mass. The purpose of this study was to determine whether serum creatinine level is associated with type 2 diabetes

Current guidelines for the implementation of flywheel resistance training technology in sports:a consensus statement

BackgroundFlywheel resistance training has become more integrated within resistance training programs in a variety of sports due to the neuromuscular, strength, and task-specific enhancements reported with this training.ObjectiveThis paper aimed to present the consensus reached by internationally recognized experts during a meeting on current definitions and guidelines for the implementation of flywheel resistance training technology in sports.MethodsNineteen experts from different countries took part in the consensus process; 16 of them were present at the consensus meeting (18 May 2023) while three submitted their recommendations by e-mail. Prior to the meeting, evidence summaries were developed relating to areas of priority. This paper discusses the available evidence and consensus process from which recommendations were made regarding the appropriate use of flywheel resistance training technology in sports. The process to gain consensus had five steps: (1) performing a systematic review of systematic reviews, (2) updating the most recent umbrella review published on this topic, (3) first round discussion among a sample of the research group included in this consensus statement, (4) selection of research group members—process of the consensus meeting and formulation of the recommendations, and (5) the consensus process. The systematic analysis of the literature was performed to select the most up-to-date review papers available on the topic, which resulted in nine articles; their methodological quality was assessed according to AMSTAR 2 (Assessing the Methodological Quality of Systematic Review 2) and GRADE (Grading Recommendations Assessment Development and Evaluation). Statements and recommendations scoring 7–9 were considered appropriate.ResultsThe recommendations were based on the evidence summary and researchers’ expertise; the consensus statement included three statements and seven recommendations for the use of flywheel resistance training technology. These statements and recommendations were anonymously voted on and qualitatively analyzed. The three statements reported a score ranging from 8.1 to 8.8, and therefore, all statements included in this consensus were considered appropriate. The recommendations (1–7) had a score ranging from 7.7 to 8.6, and therefore, all recommendations were considered appropriate.ConclusionsBecause of the consensus achieved among the experts in this project, it is suggested that practitioners and researchers should adopt the guidelines reported in this consensus statement regarding the use of flywheel resistance technology in sports

Reduced firing rates of high threshold motor units in response to eccentric overload

Acute responses of motor units were investigated during submaximal voluntary isometric tasks following eccentric overload (EO) and constant load (CL) knee extension resistance exercise. Ten healthy resistance-trained participants performed four experimental test sessions separated by 5 days over a 20 day period. Two sessions involved constant load and the other two used eccentric overload. EO and CL used both sessions for different target knee eccentric extension phases; one at 2 sec and the other at 4 sec. Maximal voluntary contractions (MVC) and isometric trapezoid efforts for 10 sec at 70% MVC were completed before and after each intervention and decomposed electromyography was used to measure motor unit firing rate. The firing rate of later recruited, high-threshold motor units declined following the 2-sec EO but was maintained following 2sec CL (P < 0.05), whereas MUFR for all motor units were maintained for both loading types following 4-sec extension phases. MVC and rate of force development where maintained following both EO and CL and 2 and 4 sec phases. This study demonstrates a slower firing rate of high-threshold motor units following fast eccentric overload while MVC was maintained. This suggests that there was a neuromuscular stimulus without cost to the force-generating capacity of the knee extensors. © 2017 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society

Injury prevention programs based on flywheel vs. body weight resistance in recreational athletes

This study compares the effect of an isoinertial flywheel technology vs. a traditional gravity-dependent exercise protocol on modifiable factors associated with the incidence of hamstring strain (HAM) and anterior cruciate ligament (ACL) injuries. Furthermore, the effect on repeated sprint ability was also considered. Eighteen recreationally trained volleyball players completed one of the following 6-week protocols: (a) flywheel (FY) included 3 exercises using a YoYo isoinertial-squat machine and 3 exercises with a Versa-Pulley isoinertial device, and (b) gravity-dependent (GT) involved 6 similar exercises with no external resistance (participants' body weight). Both programs consisted in 2 sessions·wk−1 performing 2 sets of 8 repetitions with 2 minutes of rest. Outcomes included a 10-second tuck jump assessment (TJA), landing knee valgus score, hamstring and quadriceps concentric and eccentric isokinetic 60°·s−1 peak torque, optimal peak torque localization, conventional and functional hamstring-to-quadriceps ratio, and 10-m repeated shuttle sprint ability (RSSA) test. FY improved TJA (−2, interquartile range [IQR] = −3 to −1) and valgus (−1, IQR = −1 to 0) scores, hamstring eccentric (20.37, 95% confidence interval [CI] = 9.27–31.47 N·m) and concentric (17.87, 95% CI = 0.40–35.34 N·m) peak torque, as well as the RSSA (−0.28, 95% CI = −0.45 to −0.10 seconds), whereas GT only improved hamstring eccentric peak torque (21.41, 95% CI = 9.00–33.82 N·m). A 6-week protocol using flywheel technology seems to elicit better positive adaptations to protect athletes from HAM and ACL injuries and to enhance RSSA performance compared to exercising with no external resistance other than athletes' body weight

Genetic variation and exercise-induced muscle damage: implications for athletic performance, injury and ageing.

Prolonged unaccustomed exercise involving muscle lengthening (eccentric) actions can result in ultrastructural muscle disruption, impaired excitation-contraction coupling, inflammation and muscle protein degradation. This process is associated with delayed onset muscle soreness and is referred to as exercise-induced muscle damage. Although a certain amount of muscle damage may be necessary for adaptation to occur, excessive damage or inadequate recovery from exercise-induced muscle damage can increase injury risk, particularly in older individuals, who experience more damage and require longer to recover from muscle damaging exercise than younger adults. Furthermore, it is apparent that inter-individual variation exists in the response to exercise-induced muscle damage, and there is evidence that genetic variability may play a key role. Although this area of research is in its infancy, certain gene variations, or polymorphisms have been associated with exercise-induced muscle damage (i.e. individuals with certain genotypes experience greater muscle damage, and require longer recovery, following strenuous exercise). These polymorphisms include ACTN3 (R577X, rs1815739), TNF (-308 G>A, rs1800629), IL6 (-174 G>C, rs1800795), and IGF2 (ApaI, 17200 G>A, rs680). Knowing how someone is likely to respond to a particular type of exercise could help coaches/practitioners individualise the exercise training of their athletes/patients, thus maximising recovery and adaptation, while reducing overload-associated injury risk. The purpose of this review is to provide a critical analysis of the literature concerning gene polymorphisms associated with exercise-induced muscle damage, both in young and older individuals, and to highlight the potential mechanisms underpinning these associations, thus providing a better understanding of exercise-induced muscle damage

Acute and early chronic responses to resistance exercise using flywheel or weights

Weight training typically offers constant external load during coupled shortening (concentric) and lengthening (eccentric) muscle actions in sets of consecutive repetitions until failure. However, skeletal muscle inherently has the capability to produce greater force in the eccentric compared with the concentric action, which allows for greater loading during the eccentric action, i.e. eccentric overload . Thus, traditional weight training uses a loading strategy, which appears to result in incomplete motor unit recruitment and muscle use during most concentric actions and all eccentric actions of a set. In contrast, the flywheel device, using the inertia of flywheel(s) to generate resistance, allows for maximal voluntary force to be produced throughout each concentric action with brief episodes of eccentric overload. This type of loading may potentially increase motor unit recruitment and muscle use during acute resistance exercise, and as a result may induce greater training adaptations when bouts are repeated. The aim of the present thesis was to explore the fatigue response of the quadriceps muscle during flywheel exercise, and to compare quadriceps muscle use and adaptations to training in response to acute or chronic resistance exercise using traditional free weights/weight stack machine or a flywheel apparatus. Multichannel surface electromyographic (EMG) signals were recorded from the quadriceps muscle of nine men, to assess fatigue during consecutive concentric-eccentric actions performed using the flywheel device. There was marked fatigue during both the concentric and eccentric actions. Results further showed a discrepancy between normalized rate of decrease of instantaneous mean power spectral frequency (iMNF) and conduction velocity (CV), which may imply that iMNF will not accurately reflect changes in CV during dynamic actions. Furthermore, to assess and compare quadriceps muscle use in the two loading features, five resistance trained men performed free weight and flywheel resistance exercise on separate days. Flywheel exercise induced greater over all muscle use, showing greater over all EMG activity and increase in transverse relaxation time (T2) of magnetic resonance images, compared with free weight exercise. The greater muscle use shown with flywheel exercise appeared to result from the greater forces produced during the flywheel compared with free weight exercise. Furthermore, when fifteen healthy men were assigned to five weeks of unilateral knee extension training using either a flywheel device or a weight stack machine, flywheel training induced more robust muscular adaptations, i.e. increased volume of all four individual quadriceps muscles and increased maximal isometric strength, compared with weight stack training. In summary, flywheel resistance exercise resulted in more robust muscular adaptations compared with traditional resistance exercise using weights. Furthermore, the flywheel device induced greater forces and muscle use during acute exercise. The marked fatigue response during the coupled concentric-eccentric flywheel exercise is supported of near maximal effort and hence muscle use, which is further suggested to, at least in part, explain the more robust muscular adaptations following chronic flywheel resistance exercise compared with traditional weight training