Effect of Velocity-Based Loading on Acceleration Kinetics and Kinematics During Sled Towing.

ABSTRACT: Bentley, I, Sinclair, JK, Atkins, SJ, Metcalfe, J, and Edmundson, CJ. Effect of velocity-based loading on acceleration kinetics and kinematics during sled towing. J Strength Cond Res 35(4): 1030-1038, 2021-Sled towing (ST) provides an external load in the form of a sled towed using a shoulder or waist harness and cord behind the athlete. Loading strategies have varied greatly between studies, and despite many investigations, there is little agreement on the optimum sled loading to develop the acceleration phase. The aim of this study was to investigate the kinetics and kinematics of velocity-based ST during the acceleration phase of sprinting. Twelve academy rugby league players performed a series of 6-m sprints in different conditions; uninhibited, 10, 15, and 20% velocity decrement (VDec). Sagittal plane kinematics and kinetic measures were examined using 1-way repeated-measures analysis of variance. Results indicated that ST affected trunk, knee, and ankle joint kinematics (p < 0.05). Peak knee flexion increased as sled loads increased (p < 0.05), which may enable athletes to lower their center of mass and increase their horizontal force application. Net horizontal and propulsive impulse measures were greater in all sled conditions (p < 0.05), which increased significantly because sled loadings were heavier. In conclusion, this study highlights the effects of differential loads to help coaches understand acute kinetics and kinematic changes to improve the planning of sprint training.

A Comparison of GPS Workload Demands in Match Play and Small-Sided Games by the Positional Role in Youth Soccer.

The external demands of small-sided games (SSGs) according to the positional role are currently unknown. Using a Catapult Minimax X3 5 Hz GPS, with a 100 Hz tri-axial accelerometer, we compared the accumulated tri-axial player workload per min (PLacc·min-1) during friendly youth match play (MP) (11 vs. 11) and SSGs (2 vs. 2, 3 vs. 3, and 4 vs. 4). Significant differences existed between all SSGs and MP for PLacc·min-1 (F = 21.91, p < 0.001, η2 = 0.38), and individual X (F = 27.40, p < 0.001, η2 = 0.43), Y (F = 14.50, p < 0.001, η2 = 0.29) and Z (F = 19.28, p < 0.001, η2 = 0.35) axis loads. Across all conditions, mean PLacc·min-1 was greater for midfielders (p = 0.004, CI: 0.68, 4.56) and forwards (p = 0.037, CI: 0.08, 3.97) than central defenders. In all conditions, greater Y axis values existed for wide defenders (p = 0.024, CI: 0.67, 1.38), midfielders (p = 0.006, CI: 0.18, 1.50) and forwards (p = 0.007, CI: 0.17, 0.15) compared to central defenders. Midfielders reported greater Z axis values compared to central defenders (p = 0.002, CI: 0.40, 2.23). We concluded that SSGs elicited greater external loads than MP, and previous studies may have underestimated the demands of SSGs.

Impact of Harness Attachment Point on Kinetics and Kinematics During Sled Towing.

Resisted sprint training is performed in a horizontal direction and involves similar muscles, velocities, and ranges of motion (ROM) to those of normal sprinting. Generally, sleds are attached to the athletes through a lead (3 m) and harness; the most common attachment points are the shoulder or waist. At present, it is not known how the different harness point's impact on the kinematics and kinetics associated with sled towing (ST). The aim of the current investigation was to examine the kinetics and kinematics of shoulder and waist harness attachment points in relation to the acceleration phase of ST. Fourteen trained men completed normal and ST trials, loaded at 10% reduction of sprint velocity. Sagittal plane kinematics from the trunk, hip, knee, and ankle were measured, together with stance phase kinetics (third footstrike). Kinetic and kinematic parameters were compared between harness attachments using one-way repeated-measures analysis of variance. The results indicated that various kinetic differences were present between the normal and ST conditions. Significantly greater net horizontal mean force, net horizontal impulses, propulsive mean force, and propulsive impulses were measured (p < 0.05). Interestingly, the waist harness also led to greater net horizontal impulse when compared with the shoulder attachment (p < 0.001). In kinematic terms, ST conditions significantly increased peak flexion in hip, knee, and ankle joints compared with the normal trials (p < 0.05). Results highlighted that the shoulder harness had a greater impact on trunk and knee joint kinematics when compared with the waist harness (p < 0.05). In summary, waist harnesses seem to be the most suitable attachment point for the acceleration phase of sprinting. Sled towing with these attachments resulted in fewer kinematic alterations and greater net horizontal impulse when compared with the shoulder harness. Future research is necessary in order to explore the long-term adaptations of these acute changes.

Effect of psychological intervention on exercise adherence in type 2 diabetic subjects.

Previous research has pointed to the efficacy of physical activity in individuals suffering from type 2 diabetes mellitus (type 2 DM). However, as with other populations, adherence to exercise programs is often problematic. This study assessed the effectiveness of a combination of exercise and psychological interventions in type 2 diabetics in terms of disease management and exercise adherence. Forty newly diagnosed type 2 diabetic subjects (54 +/- 6.5 years) took part in the study. Subjects were allocated to an exercise-only intervention (EO) or a combined exercise and psychological adherence intervention (EP) group. Adherence to the program was also monitored at a 6-month follow-up. The results confirmed a significant improvement in physiological parameters (total mass, fat mass, grip strength, peak flow, flexibility, and VO2 max) after the 12-week program in both groups (P < 0.001). The EP group had significant changes in body fat, grip strength, and peak flow (P < 0.05) in comparison to the EO group. Components of the visual analog mood scale (VAMS) were positively influenced in both groups from the therapy program (P < 0.001). The directed psychological intervention had a significant influence on attendance to the 12-week program (P < 0.001). This also resulted in significantly better adherence 6 months later (P < 0.05). In conclusion, the results have demonstrated that psychological intervention is of paramount importance for ensuring high adherence rates during exercise therapy for type 2 diabetic subjects.

Critical review of health effects of soyabean phyto-oestrogens in post-menopausal women.

A consensus view of soyabean phyto-oestrogens in clinical interventions in post-menopausal women is presented that is based on data from the EU-funded project Phytohealth. The phyto-oestrogens, primarily genistein and daidzein, were given as soyabean-protein isolates, whole-soyabean foods or extracts, supplements or pure compounds. A comprehensive literature search was conducted with well-defined inclusion or exclusion criteria. For areas for which substantial research exists only placebo-controlled double-blind randomised controlled trials (RCT) conducted on healthy post-menopausal women were included. For emerging areas all available human studies in post-menopausal women were reviewed. In order to make cross comparisons between studies the doses of isoflavones were calculated as aglycone equivalents. There is a suggestion, but no conclusive evidence, that isoflavones from the sources studied so far have a beneficial effect on bone health. The consumption of whole-soyabean foods and soyabean-protein isolates has some beneficial effects on lipid markers of cardiovascular risk. The consumption of isolated isoflavones does not affect blood lipid levels or blood pressure, although it may improve endothelial function. For menopausal symptoms there is currently limited evidence that soyabean-protein isolates, soyabean foods or red-clover (Trifolium pratense L.) extract are effective but soyabean isoflavone extracts may be effective in reducing hot flushes. There are too few RCT studies to reach conclusions on the effects of isoflavones on breast cancer, colon cancer, diabetes or cognitive function. The health benefits of soyabean phyto-oestrogens in healthy post-menopausal women are subtle and even some well-designed studies do not show protective effects. Future studies should focus on high-risk post-menopausal women, especially in the areas of diabetes, CVD, breast cancer and bone health.