The influence of golf club shaft stiffness on clubhead kinematics at ball impact

The role of shaft stiffness on the golf swing is not well understood. Studies in which golfers hit balls with clubs of varying shaft flex have reported changes in ball distance. The results of mathematical models suggest that shaft stiffness affects only the orientation of the clubhead at impact, not the speed of the clubhead, but there are no experimental results validating these findings. The purpose of this study was therefore to experimentally examine the influence of shaft stiffness on clubhead kinematics at ball impact. Forty golfers hit 10 balls with each of five drivers varying in shaft stiffness from 'Ladies' to 'Extra-Stiff', in a double-blind study design. The motions of three reflective markers attached to the clubhead were captured with a high-speed motion analysis system. At ball impact, shaft stiffness had a statistically significant influence on clubhead speed for 27 subjects, on loft angle for 11 subjects, and on lie angle for all 40 subjects. No effect was observed on face angle, in to out path angle, or attack angle. These results show that shaft stiffness can affect ball launch conditions by altering clubhead speed and/or loft angle.     

The impact of high-stakes testing on student proficiency in low-stakes subjects: Evidence from Florida's elementary science exam

An important criticism of high-stakes testing policies – policies that reward or sanction schools based on their students’ performance on standardized tests – is that they provide schools with an incentive to focus on those subjects that play a role in the accountability system while decreasing attention to those subjects that are not part of the program. This paper utilizes a regression discontinuity design to evaluate the impact of Florida's high-stakes testing policy on student proficiency in the low-stakes subject of science. We confirm prior results that students in schools facing more immediate sanctions under the policy made substantial gains in the high-stakes subjects of math and reading. Contrary to the crowding-out hypothesis, we find that students in these schools made substantial achievement gains in the low-stakes subject of science as well.     

The influence of isometric preload on power expressed during bench press in strength-trained men

The purpose of this study was to compare the power expressed during the bench press exercise in resistance-trained men following different pre-activation conditions. Twenty-two trained men (age 24.1?±?1.7 years, height 178.6?±?6.1?cm, body mass 81.1?±?10.6?kg) completed a maximal effort bench press (1-RM) test (100.0?kg?±?8.1?kg). In a subsequent assessment, each participant performed concentric bench press movements with loads of 20%, 30%, 40% and 50% of their 1-RM preceded by either a concentric contraction (CC), a low isometric preload (LIP; 70% 1-RM) or a high isometric preload (HIP; 100% 1-RM) conditions. All movements were performed in a Smith machine with a settable quick-release device. Participants performed all three conditions in randomized fashion. Results indicated that power outputs during the bench press exercise following HIP were significantly (p?<?0.05) greater than CC at 20% 1-RM (+9%), 30% 1-RM (+16%) and 40% 1-RM (+14%), and LIP at 20% 1-RM (+4%), 30% 1-RM (+20%) and 40% 1-RM (+15%). No differences were found between conditions at 50% 1-RM. Area under the force–power curve with HIP was greater (p?<?0.05) than with CC and LIP. In conclusion, results of this study indicate that the use of a HIP (100% 1-RM) in trained participants results in significantly greater power output during the concentric phase of a multi-joint exercise when compared to standard concentric movement.