The impact of hamstring holds or lengthening exercises on strength, muscle architecture and morphology.

This research will require participants to undertake a 6-week training intervention with either an isometric or eccentric hip extension exercise which are designed to improve the strength and size of your hamstring muscles. Participants will be randomly enrolled (based on their muscle ultrasound results) into a progressive intensity training program with each session lasting no more than 30min in duration. The volume and intensity of the exercise sessions will be gradually increased throughout the training period to minimise the risk of injury and to allow for progressive overload (gradual improvements in strength over time). For example, in the first training session participants will complete lower amounts of repetitions compared to their final session where they will be completing the efforts with additional weight and more repetitions. isometric hip extension: to be used during the isometric intervention Participants will be placed on a hip extension device and asked to contract while not moving. They will undertake this using one leg, with the opposite limb acting as a control comparison. Once they become proficient at a certain intensity, then will be added weight to ensure all efforts are undertaken at perceived intensities >8 out of 10. eccentric hip extension: to be used during the eccentric intervention Participants will be placed on a hip extension device and asked to contract while lowering their upper body. They will undertake this using one leg, with the opposite limb acting as a control comparison. Once they become proficient at a certain intensity, then will be added weight to ensure all efforts are undertaken at perceived intensities >8 out of 10. Isometric exercise intervention: Week 1 – 2 sessions, 4 repetitions, 10 seconds each repetition = 80 seconds Week 2 – 2 sessions, 4 repetitions, 10 seconds each repetition = 80 seconds Week 3 – 2 sessions, 4 repetitions, 10 seconds each repetition = 80 seconds Week 4 – 2 sessions, 6 repetitions, 10 seconds each repetition = 120 seconds Week 5 – 2 sessions, 6 repetitions, 10 seconds each repetition = 160 seconds Week 6 – 2 sessions, 6 repetitions, 10 seconds each repetition = 200 seconds All efforts will be performed at a perceived intensity of >8 out of 10, whilst correct exercise technique was maintained. Once intensity is <8, additional weight will be held across the chest by the participant. Eccentric exercise intervention: Week 1 – 2 sessions, 2 sets, 4 repetitions, 5 second per repetition = 80 seconds Week 2 – 2 sessions, 2 sets, 4 repetitions, 5 second per repetition = 80 seconds Week 3 – 2 sessions, 2 sets, 4 repetitions, 5 second per repetition = 80 seconds Week 4 – 2 sessions, 3 sets, 4 repetitions, 5 second per repetition = 120 seconds Week 5 – 2 sessions, 4 sets, 4 repetitions, 5 second per repetition = 160 seconds Week 6 – 2 sessions, 5 sets, 4 repetitions, 5 second per repetition = 200 seconds All efforts will be performed at a perceived intensity of >8 out of 10, whilst correct exercise technique was maintained. Once intensity is <8, additional weight will be held across the chest by the participant. The intervention for each participant will be personalised to their perception of intensity. The researchers will ask the participant how they rate the intensity of effort following each effort. The weight held to their chest will then be modified to ensure each repetition was performed at perceived intensities >8 out of 10 with 10 as an absolutely maximum and 1 being no effort at all. Adherence to the intervention will be monitored via a session attendance checklist (Yes/No) with the number of total attended sessions being used to compare compliance between the groups.