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

INTERVENTION: 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 seco CONDITION: Hamstring injuries;Sport injuries; ; Hamstring injuries ; Sport injuries Injuries and Accidents ‐ Other injuries and accidents Musculoskeletal ‐ Other muscular and skeletal disorders PRIMARY OUTCOME: Biceps femoris long head fascicle length[Timepoint: baseline (one week after randomisation), mid‐training (beginning week 4 of training), post training (5‐7 days after last training session – 7 weeks after baseline ‐ primary timepoint), end no‐training (28 days after the post training assessment); ; Instrument: two‐dimensional ultrasound extended field of view images as well as small field of view images.; ] SECONDARY OUTCOME: Biceps femoris long head muscle anatomical cross‐sectional area[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans + ultrasound ; ] Biceps femoris long head muscle aponeurosis geometry[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] Biceps femoris long head muscle physiological cross‐sectional area[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans + ultrasound ; ; Instrument: two‐dimensional ultrasound extended field of view images as well as small field of view images. ; Instrument: MRI scans ; ; Instrument: two‐dimensional ultrasound extended field of view images as well as small field of view images. ; Instrument: MRI scans ; Instrument: MRI scans ; Instrument: MRI scans ; Instrument: Nordbord (commercially made device) ; Instrument: MRI scans ; Instrument: MRI scans ; Instrument: MRI scans ; ] Biceps femoris long head muscle thickness[Timepoint: baseline (one week after randomisation), mid‐training (beginning week 4 of training), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] Biceps femoris long head muscle volume[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] Biceps femoris long head pennation angle[Timepoint: baseline (one week after randomisation), mid‐training (beginning week 4 of training), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] Biceps femoris short head muscle aponeurosis geometry[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] Biceps femoris short head muscle cross‐sectional area (anatomical)[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] Biceps femoris short head muscle volume[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] Bilateral, peak Nordic hamstring exercise force[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] gluteal muscle aponeurosis geometry[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] gluteal muscle cross‐sectional area (anatomical)[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] gluteal muscle volume[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; ] hamstring bridge to fatigue test[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: 60cm box, unilateral, bridge until fatigue ; ] semimembranosus muscle aponeurosis geometry[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] semimembranosus muscle cross‐sectional area (anatomical)[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] semimembranosus muscle volume[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] semitendinosus muscle aponeurosis geometry[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] semitendinosus muscle cross‐sectional area (anatomical)[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] semitendinosus muscle volume[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] trunk extensor muscle aponeurosis geometry[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] trunk extensor muscle cross‐sectional area (anatomical)[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] trunk extensor muscle volume[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: MRI scans ; ] Unilateral, concentric average peak hamstring torque during 180deg/sec[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: isokinetic dynamometer ; ] Unilateral, concentric average peak hamstring torque during 60deg/sec[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: isokinetic dynamometer ; ] Unilateral, eccentric average peak hamstring torque during 180deg/sec[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: isokinetic dynamometer ; ] Unilateral, eccentric average peak hamstring torque during 60deg/sec[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: isokinetic dynamometer ; ] Unilateral, isometric peak hamstring torque at 30deg[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment) ; Instrument: isokinetic dynamometer ; Instrument: ForceFrame (commercially made device) ; ] INCLUSION CRITERIA: Healthy, recreationally active males ; ] Unilateral, isometric prone hip extension force[Timepoint: baseline (one week after randomisation), post training (5‐7 days after last training session – 7 weeks after baseline), end no‐training (28 days after the post training assessment)