Determining the Effect of Shoulder Flexion Angle on Latissimus Dorsi and Forearm Flexor Hypertrophy

Determining the Effect of Shoulder Flexion Angle on Latissimus Dorsi and Forearm Flexor Hypertrophy

The goal of this clinical trial is to learn the effect of training a muscle at a longer or shorter muscle length during resistance exercise in young and healthy adults. Participants will undergo two types of resistance training conditions that are randomly assigned to the left and right arm. The LATPULLDOWN (LPD) condition refers to performing an exercise that places the latissimus dorsi muscle at a long muscle length when the shoulder is elevated to 180° of shoulder flexion. The LATROW (LR) condition refers to performing an exercise that places the latissimus dorsi muscle at a shorter muscle length when the shoulder is elevated to 90° of shoulder flexion.

The main questions the trial aims to answer are:

1. Does resistance training the latissimus dorsi muscle at a long muscle length result in greater muscle growth than training at a shorter muscle length?
2. Does resistance training the latissmus dorsi muscle at long or short muscle lengths result in regional muscle growth differences of the latissimus dorsi?

We hypothesize that:

1. LAT PULLDOWN will induce greater hypertrophy compared to LAT ROW condition
2. LAT PULLDOWN will result in greater increases in 1RM compared to LATROW condition
3. LAT PULLDOWN and LAT ROW will result in angle specific differences in Isokinetic strength
4. LAT PULLDOWN will result in greater inferior Latissimus Dorsi hypertrophy
5. LAT ROW will result in greater superior Latissimus Dorsi hypertrophy

The investigators will compare the change in muscle volume and muscular strength between the LAT PULLDOWN and LAT ROW training conditions, which each participant will have the left and right arm randomly assigned to either exclusively LAT PULLDOWN or LAT ROW conditions.

Participants will:

• Resistance train the left and right arm with two separate conditions; LAT PULLDOWN and LAT ROW 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 and isokinetic strength between LAT PULLDOWN and LAT ROW 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%.

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. Trained participants: Structured resistance training over at least the past 12-months (i.e., ≥ 2 hours per week of structured/periodized training)

Exclusion Criteria:

Participants will be excluded from this study if they meet any of the following 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. Implants containing ferrous metal
10. Surgery or tattoos (including tattooed eyeliner) in the last 6 weeks
11. Pregnancy

Magnetic Resonance Imaging (MRI) Exclusion Criteria

CANNOT participate if you have any of the following:

1. Retained wires from an electronic implant that has been removed (i.e., pacemaker wires not attached to a pacemaker)
2. Cardiac pacemaker or defibrillator
3. Metal in eye or orbit
4. Ferromagnetic aneurysm clip
5. Makeup tattoos that are not designed to fade over time
6. Stainless steel intrauterine device (IUD)

Depending on the individual situation, you may not be able to participate if you have/had any of the following:

1. Artificial heart valve
2. Ear or eye implant
3. Brain aneurysm clip
4. Implanted electronic device (i.e., drug infusion pump, electrical stimulator)
5. Orthopedic hardware (artificial joint, plate, screw, rod)
6. Shrapnel, bullets, or other metal fragments
7. Surgery, medical procedure, or tattoos (including tattooed eyeliner) in the last six weeks
8. Other metallic prostheses