Dynamic Strength Index: Relationships with Common Performance Variables and Contextualization of Training Recommendations

The purposes of this study were to examine the relationships between dynamic strength index (DSI) and other strength-power performance characteristics and to contextualize DSI scores using case study comparisons. 88 male and 67 female NCAA division I collegiate athletes performed countermovement jumps (CMJ) and isometric mid-thigh pulls (IMTP) during a pre-season testing session as part of a long-term athlete monitoring program. Spearman\u27s correlations were used to assess the relationships between DSI and CMJ peak force, height, modified reactive strength index, peak power and IMTP peak force and rate of force development (RFD). Very large relationships existed between DSI and IMTP peak force (r = -0.848 and -0.746), while small-moderate relationships existed between DSI and CMJ peak force (r = 0.297 and 0.313), height (r = 0.108 and 0.167), modified reactive strength index (r = 0.174 and 0.274), and IMTP RFD (r = -0.341 and -0.338) for men and women, respectively. Finally, relationships between DSI and CMJ peak power were trivial-small for male (r = 0.008) and female athletes (r = 0.191). Case study analyses revealed that despite similar DSI scores, each athlete\u27s percentile rankings for each variable and CMJ force-time characteristics were unique, which may suggest different training emphases are needed. Based on the explained variance, an athlete\u27s IMTP performance may have a larger influence on their DSI score compared to the CMJ. DSI scores should be contextualized using additional performance data to ensure each individual athlete receives the appropriate training stimulus during different training phases throughout the year

Mechanical Properties of Molybdenum Disulfide and the Effect of Doping: An in Situ TEM Study

Direct observations on nanopillars composed of molybdenum disulfide (MoS₂) and chromium-doped MoS₂ and their response to compressive stress have been made. Time-resolved transmission electron microscopy (TEM) during compression of the submicrometer diameter pillars of MoS₂- and Cr-doped MoS₂ (Cr: 0, 10, and 50 at %) allow the deformation process of the material to be observed and can be directly correlated with mechanical response to applied load. The addition of chromium to the MoS₂ changed the failure mode from plastic deformation to catastrophic brittle fracture, an effect that was more pronounced as chromium content increased

Persistent frequent attenders in primary care: costs, reasons for attendance, organisation of care and potential for cognitive behavioural therapeutic intervention

<p><b>Abstract</b></p> <p>Background</p> <p>The top 3% of frequent attendance in primary care is associated with 15% of all appointments in primary care, a fivefold increase in hospital expenditure, and more mental disorder and functional somatic symptoms compared to normal attendance. Although often temporary if these rates of attendance last more than two years, they may become persistent (persistent frequent or regular attendance). However, there is no long-term study of the economic impact or clinical characteristics of regular attendance in primary care. Cognitive behaviour formulation and treatment (CBT) for regular attendance as a motivated behaviour may offer an understanding of the development, maintenance and treatment of regular attendance in the context of their health problems, cognitive processes and social context.</p> <p>Methods/design</p> <p>A case control design will compare the clinical characteristics, patterns of health care use and economic costs over the last 10 years of 100 regular attenders (≥30 appointments with general practitioner [GP] over 2 years) with 100 normal attenders (6–22 appointments with GP over 2 years), from purposefully selected primary care practices with differing organisation of care and patient demographics. Qualitative interviews with regular attending patients and practice staff will explore patient barriers, drivers and experiences of consultation, and organisation of care by practices with its challenges. Cognitive behaviour formulation analysed thematically will explore the development, maintenance and therapeutic opportunities for management in regular attenders. The feasibility, acceptability and utility of CBT for regular attendance will be examined.</p> <p>Discussion</p> <p>The health care costs, clinical needs, patient motivation for consultation and organisation of care for persistent frequent or regular attendance in primary care will be explored to develop training and policies for service providers. CBT for regular attendance will be piloted with a view to developing this approach as part of a multifaceted intervention.</p

Effect of Traditional Vs. Modified Bent-Knee Sit-Up On Abdominal and Hip Flexor Muscle Electromyographic Activity

The traditional sit-up may be a poor choice for core strength training due to its focus on hip flexion. The purpose of this study was to determine differences in abdominal and hip flexor muscle activation and trunk and hip kinematics between the traditional U.S. Army sit-up and a modified sit-up focusing on trunk flexion. Eighteen trained males performed 30 seconds of repetitions of each sit-up style, while muscle activation of the rectus abdominis (RA), external oblique (EO), and rectus femoris (RF) was recorded using electromyography (EMG). Trunk and hip kinematics were measured using 2-D videography. Maximum and mean muscle activation, integrated EMG (iEMG), and trunk and hip flexion were compared using a repeated-measures design. Maximum EMG of the RF and EO and mean EMG and iEMG of the RF were greater during the traditional sit-up. In contrast, mean EMG and iEMG of the RA and EO were greater during the modified sit-up. Peak trunk flexion was greater during the modified sit-up, and peak hip flexion was greater during the traditional sit-up. The greater RF EMG activity and peak hip flexion during the traditional sit-up suggest a greater emphasis on hip flexion during this sit-up style, which may result in lumbar hyperextension. The greater RA and EO activity and peak trunk flexion during the modified sit-up suggest a greater emphasis on trunk flexion during this exercise, which may decrease the lumbar spine load. Therefore, the modified sit-up may be a better exercise selection to train the abdominal muscles

The importance of muscular strength: Training considerations

This review covers underlying physiological characteristics and training considerations that may affect muscular strength including improving maximal force expression and time-limited force expression. Strength is underpinned by a combination of morphological and neural factors including muscle cross-sectional area and architecture, musculotendinous stiffness, motor unit recruitment, rate coding, motor unit synchronization, and neuromuscular inhibition. Although single- and multi-targeted block periodization models may produce the greatest strength-power benefits, concepts within each model must be considered within the limitations of the sport, athletes, and schedules. Bilateral training, eccentric training and accentuated eccentric loading, and variable resistance training may produce the greatest comprehensive strength adaptations. Bodyweight exercise, isolation exercises, plyometric exercise, unilateral exercise, and kettlebell training may be limited in their potential to improve maximal strength but are still relevant to strength development by challenging time-limited force expression and differentially challenging motor demands. Training to failure may not be necessary to improve maximum muscular strength and is likely not necessary for maximum gains in strength. Indeed, programming that combines heavy and light loads may improve strength and underpin other strength-power characteristics. Multiple sets appear to produce superior training benefits compared to single sets; however, an athlete’s training status and the dose–response relationship must be considered. While 2- to 5-min interset rest intervals may produce the greatest strength-power benefits, rest interval length may vary based an athlete’s training age, fiber type, and genetics. Weaker athletes should focus on developing strength before emphasizing power-type training. Stronger athletes may begin to emphasize power-type training while maintaining/improving their strength. Future research should investigate how best to implement accentuated eccentric loading and variable resistance training and examine how initial strength affects an athlete’s ability to improve their performance following various training methods

Strength Training for Endurance Athletes: Theory to Practice

The purpose of this review is twofold: to elucidate the utility of resistance training for endurance athletes, and provide the practitioner with evidenced-based periodization strategies for concurrent strength and endurance training in athletic populations. Both low-intensity exercise endurance (liee) and high-intensity exercise endurance (hiee) have been shown to improve as a result of maximal, high force, low velocity (hflv) and explosive, low-force, high-velocity strength training. Hflv strength training is recommended initially to develop a neuromuscular base for endurance athletes with limited strength training experience. A sequenced approach to strength training involving phases of strength-endurance, basic strength, strength, and power will provide further enhancements in liee and hiee for high-level endurance athletes

Defining the Early, Mid, and Late Sub-Sections of Sprint Acceleration in Division I Men’s Soccer Players

The purpose of this study was to investigate whether the acceleration phase of sprinting could be split into subphases specific to the competitive demands of a soccer match by comparing sprint metrics at various sprint distances in Division I men\u27s soccer players. Twenty-three Division I men\u27s soccer athletes completed 2 maximal-effort 20-m sprints from a standing start position through an optical measurement system. Sprint metrics measured included sprint velocity (SV), step length (SL), step frequency (SF), and ground contact time (GCT). Each metric was recorded at approximately 2.5, 6, and 12 m. Sprint metrics at each distance were compared using a 2-tailed, 1-way repeated-measures analysis of variance. The results indicated that SV, SL, and SF were statistically greater at 12 m in comparison with 6 m (p \u3c 0.001) and 2.5 m (p \u3c 0.001), whereas GCT was statistically shorter at 12 m compared with 6 m (p \u3c 0.001) and 2.5 m (p \u3c 0.001). In addition, sprint metrics at 6 m also displayed the same relationships when compared to 2.5 m, with SV, SL, and SF being statistically greater (p \u3c 0.001) at this distance, and GCT being statistically shorter (p \u3c 0.001) as well. These results suggest that the acceleration phase may effectively be differentiated into early, mid, and late subphases based on differences in key sprint metrics at distances of 2.5, 6, and 12 m, respectively, in Division I men\u27s soccer athletes

Training for muscular strength: Methods for monitoring and adjusting training intensity

Linear loading, the two-for-two rule, percent of one repetition maximum (1RM), RM zones, rate of perceived exertion (RPE), repetitions in reserve, set-repetition best, autoregulatory progressive resistance exercise (APRE), and velocity-based training (VBT) are all methods of adjusting resistance training intensity. Each method has advantages and disadvantages that strength and conditioning practitioners should be aware of when measuring and monitoring strength characteristics. The linear loading and 2-for-2 methods may be beneficial for novice athletes; however, they may be limited in their capacity to provide athletes with variation and detrimental if used exclusively for long periods of time. The percent of 1RM and RM zone methods may provide athletes with more variation and greater potential for strength–power adaptations; however, they fail to account for daily changes in athlete’s performance capabilities. An athlete’s daily readiness can be addressed to various extents by both subjective (e.g., RPE, repetitions in reserve, set-repetition best, and APRE) and objective (e.g., VBT) load adjustment methods. Future resistance training monitoring may aim to include a combination of measures that quantify outcome (e.g., velocity, load, time, etc.) with process (e.g., variability, coordination, efficiency, etc.) relevant to the stage of learning or the task being performed. Load adjustment and monitoring methods should be used to supplement and guide the practitioner, quantify what the practitioner ‘sees’, and provide longitudinal data to assist in reviewing athlete development and providing baselines for the rate of expected development in resistance training when an athlete returns to sport from injury or large training load reductions