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

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

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