One very common axiom amongst Strength and Conditioning Professionals and Athletic Performance Coaches is that the least flexible athletes usually produce the fastest 40-yard dash times. Flexibility, in this case specifically refers to posterior chain flexibility (PCF). This is usually measured by athletes ability to perform a sit-and-reach test. This train of thought has been widely accepted within the human performance professions, even though it is void of any scientific investigation or measured validity. The purpose of this study is to determine if there is a relationship between posterior chain flexibility using the sit-and-reach test and speed in the 40-yard dash. All test subjects were male between the ages of 18-22, and members of a Division I university football team. All 95 test subjects had participated in at least one semester of a strength and conditioning program designed by Certified Strength and Conditioning Specialists. Similar of the study done by Johnson (2001), each athlete was placed in a group based on position, line of scrimmage groups (LOS), Skill group (receivers, cornerbacks, rover linebackers, whip linebackers, and safeties), Combo group (inside linebackers, tight ends, quarterbacks, tailbacks, fullbacks, and defensive ends), Specialist group (place- kickers, kick-off specialists, holders, and punters). Each test subject was tested in the 40-yard dash, the sit-and-reach flexibility test, as well as other tests for strength and power such as the bench press, front squat, push jerk, power clean, vertical jump, and agility tests. Body weight and height was also measured. This study used a simple linear regression on the data where the Sit-and-Reach test results were the dependent variable and the subjects timed results in a 40 yard dash was the independent variable. There appears to be no significant relationship between a low flexibility score and the sprint speed of an athlete for the entire group population. The results also show that there is no significant relationship between flexibility of the posterior chain and linear speed as measured in the 40-yard dash when looking at football players that fall under the Combo, Skill, or LOS position groups. There was however a significant relationship for the specialist group. The theory that the least flexible athletes usually produce the fastest 40-yard dash times is not true for those specific groups. / Ph. D.

Title: Posterior chain muscle endurance and arm paddling peak power in amateur female surfers Objectives: Thesis is dedicated to female surfing, particularly paddling, as this is an undiscovered area of research. Very few studies have been carried out, which would focus on muscle activity in surfing. None of the studies focused on posterior chain or muscle activity of female surfers while paddling. Not only that the level of competitive surfing is increasing rapidly, as it will be part of Olympic Games in Tokyo in 2020, but the recreational surfers are also becoming more literate about surf science and willing to improve their surfing performance by dry land surf specific trainings. Surfing industry represents a worldwide business, where big companies offer sponsorship, which is reasonable motivation for young athletes (M. Mendez-Villanueva & Bishop, 2005). As the number of recreational and competitive female surfers is raising as well, the level of competitive female surfing is increasing (Booth, 2001) and professional female surfers are becoming equal in regards to getting the same amount of prize money in competitions, more research should be dedicated to female surfing. The aim of this thesis was to study association between posterior chain endurance and other variables such as frequency of...