the effect of peak force at long and short muscle lengths and the impact on muscle growth and strength

Conditions: Muscle Hypertrophy; Muscular Strength

Summary: the goal of this clinical trial is to learn the effect of applying peak force/resistance to skeletal muscles during resistance exercise training in young and healthy adults. participants will undergo two types of resistance training conditions that are randomly assigned to the left arm and leg and the right arm and leg. the long condition refers to prime fitness machines set to setting number '3' which applies peak force at a long muscle length. the short condition refers to prime fitness machines set to setting number '2' which applies peak force at a short muscle length. the main questions the trial aims to answer are: 1. does applying peak force at a longer or shorter muscle length during resistance exercise training result in greater muscle growth? 2. does applying peak force at a longer or shorter muscle length during resistance exercise training result in greater muscle growth? we hypothesize that: 1. long will induce greater hypertrophy compared to short conditions 2. long will result in greater increases in 1rm strength compared to short 3. long and short training will result in angle specific increases in isokinetic strength 4. muscle oxygenation will decline to a greater degree during long compared to short exercise and this will be maintained between weeks 1 and 12 of training the investigators will compare the change in muscle volume and muscular strength between the long and short training conditions, which each participant will have the left arm and leg as well as the right arm and leg randomly assigned to either exclusively long or short conditions. participants will: * resistance train the left and right arm and leg with two separate conditions; long and short for 12 weeks, with the first and last weeks dedicated to only strength testing (isotonic and isokinetic) and measuring muscle volume via magnetic resonance imaging (mri) * visit the gym for resistance training 2 times per week * visit the ubc mri research facility in weeks 1 and 12 for mri of muscle volume

statistical analysis: null hypothesis significance testing (nhst) will be used to measure differences in hypertrophy, differences in 1rm strength, isokinetic strength and muscle oxygenation between long and short conditions. it is anticipated that this study will require at least 20 participants to be screened and registered into the trial. data will be analyzed on the basis that all participants will be included in the analysis. participants who drop out (withdraw from treatment) will be followed up with to collect all available data and will not be replaced. missing data will be assumed missing at random. sample size calculation: based on the effect size reported by maeo et al. (2023) for difference in triceps brachia long head hypertrophy between training performed in the lengthened compared to shortened position using a within participant design, (d=0.61) a sample size of 20 participants was calculated to achieve an a priori power of 90%.

Eligibility criteria:
inclusion criteria: 1. any sex 2. able to understand and communicate in english 3. 19-30 years of age 4. all "no" answers on the csep get active questionnaire or doctors' approval to participate 5. untrained participants: no structured resistance training over the past 12-months (i.e. \> 2 hours per week of structured/periodized training) exclusion criteria: 1. bmi lower than 18 or greater than 30 2. difficulty to understand and communicate in english 3. current use of cigarettes or other nicotine devices 4. any major uncontrolled cardiovascular, muscular, metabolic, and/or neurological disorders 5. any medical condition impacting the ability to participate in maximal exercise 6. type one or type two diabetes 7. diagnosis of cancer or undergoing cancer treatment in the past 12 months 8. drug therapy with any drugs that alter skeletal muscle metabolism (i.e., metformin, benzodiazepines) 9. omega-3 (epa, dha, fish oil) supplementation within the previous 6 weeks 10. implants containing ferrous metal 11. surgery or tattoos (including tattooed eyeliner) in the last 6 weeks 12. pregnancy

Keywords: muscle hypertrophy muscular strength long muscle lengths peak force length-tension relationship range of motion neuromechanical matching resistance training muscle oxygenation