Joint-level determinants of the dynamic strength index: implications for testing and monitoring.

The aims of this study were to determine the associations and differences between the traditional dynamic strength index (DSI, calculated from ground reaction force [GRF] data) and joint-level dynamic strength indices (DSI, calculated from net joint moment [NJM] data). Eight female NCAA Division I lacrosse players performed three maximal effort isometric mid-thigh pulls (IMTP) and countermovement jumps (CMJ). GRF and motion capture data were recorded and used to calculate hip, knee, and ankle NJM.

Maximal Strength in Relation to Force and Velocity Patterns During Countermovement Jumps.

Unlabelled: Maximal strength is important for the performance of dynamic athletic activities, such as countermovement jumps (CMJ). Although measures of maximal strength appear related to discrete CMJ variables, such as peak ground reaction forces (GRF) and center-of-mass (COM) velocity, knowledge about the association between strength and the time series patterns during CMJ will help characterize changes that can be expected in dynamic movement with changes in maximal strength.

Purpose: To investigate the associations between maximal strength and GRF and COM velocity patterns during CMJ.

Influence of the Bar Position on Joint-Level Biomechanics During Isometric Pulling Exercises.

Ahn, N, Kim, H, Krzyszkowski, J, Roche, S, and Kipp, K. Influence of the bar position on joint-level biomechanics during isometric pulling exercises. J Strength Cond Res 35(6): 1484-1490, 2021-The purpose of this study was to investigate the influence of the bar position on ankle, knee, and hip net joint moments (NJMs), relative muscular effort (RME), and vertical ground reaction forces (GRFs) during isometric pulling exercises, such as the isometric midthigh pull.

Impulse-Based Dynamic Strength Index: Considering Time-Dependent Force Expression.

Haischer, MH, Krzyszkowski, J, Roche, S, and Kipp, K. Impulse-based dynamic strength index: considering time-dependent force expression. J Strength Cond Res 35(5): 1177-1181, 2021-The dynamic strength index (DSI) is a useful tool to assess an athlete's capacity to effectively use maximum strength during dynamic tasks.

Assessment of the Contractile Properties of Permeabilized Skeletal Muscle Fibers.

Permeabilized individual skeletal muscle fibers offer the opportunity to evaluate contractile behavior in a system that is greatly simplified, yet physiologically relevant. Here we describe the steps required to prepare, permeabilize and preserve small samples of skeletal muscle. We then detail the procedures used to isolate individual fiber segments and attach them to an experimental apparatus for the purpose of controlling activation and measuring force generation.

Stromal vascular stem cell treatment decreases muscle fibrosis following chronic rotator cuff tear.

Purpose: Rotator cuff injuries are associated with atrophy and fat infiltration into the muscle, commonly referred to as "fatty degeneration." As the poor function of chronically torn muscles may limit recovery after surgical repair, there is considerable interest in finding therapies to enhance muscle regeneration. Stromal vascular fraction stem cells (SVFCs) can improve muscle regeneration in other chronic injury states, and our objective was to evaluate the ability of SVFCs to reduce fibrosis and fat accumulation, and enhance muscle fibre specific force production after chronic rotator cuff tear.

Measurement of Maximum Isometric Force Generated by Permeabilized Skeletal Muscle Fibers.

Analysis of the contractile properties of chemically skinned, or permeabilized, skeletal muscle fibers offers a powerful means by which to assess muscle function at the level of the single muscle cell. Single muscle fiber studies are useful in both basic science and clinical studies. For basic studies, single muscle fiber contractility measurements allow investigation of fundamental mechanisms of force production, and analysis of muscle function in the context of genetic manipulations.

Changes in skeletal muscle and tendon structure and function following genetic inactivation of myostatin in rats.

Myostatin is a negative regulator of skeletal muscle and tendon mass. Myostatin deficiency has been well studied in mice, but limited data are available on how myostatin regulates the structure and function of muscles and tendons of larger animals. We hypothesized that, in comparison to wild-type (MSTN(+/+) ) rats, rats in which zinc finger nucleases were used to genetically inactivate myostatin (MSTN(Δ/Δ) ) would exhibit an increase in muscle mass and total force production, a reduction in specific force, an accumulation of type II fibres and a decrease and stiffening of connective tissue.

Inhibition of 5-LOX, COX-1, and COX-2 increases tendon healing and reduces muscle fibrosis and lipid accumulation after rotator cuff repair.

Background: The repair and restoration of function after chronic rotator cuff tears are often complicated by muscle atrophy, fibrosis, and fatty degeneration of the diseased muscle. The inflammatory response has been implicated in the development of fatty degeneration after cuff injuries. Licofelone is a novel anti-inflammatory drug that inhibits 5-lipoxygenase (5-LOX), as well as cyclooxygenase (COX)-1 and COX-2 enzymes, which play important roles in inducing inflammation after injuries.

Reduced muscle fiber force production and disrupted myofibril architecture in patients with chronic rotator cuff tears.

Background: A persistent atrophy of muscle fibers and an accumulation of fat, collectively referred to as fatty degeneration, commonly occur in patients with chronic rotator cuff tears. The etiology of fatty degeneration and function of the residual rotator cuff musculature have not been well characterized in humans. We hypothesized that muscles from patients with chronic rotator cuff tears have reduced muscle fiber force production, disordered myofibrils, and an accumulation of fat vacuoles.

Aging-associated exacerbation in fatty degeneration and infiltration after rotator cuff tear.

Background: Rotator cuff tears are one of the most common musculoskeletal complaints and a substantial source of morbidity in elderly patients. Chronic cuff tears are associated with muscle atrophy and an infiltration of fat to the area, a condition known as "fatty degeneration." To improve the treatment of cuff tears in elderly patients, a greater understanding of the changes in the contractile properties of muscle fibers and the molecular regulation of fatty degeneration is essential.