Subjects
Materials and Methods
Subjects were 30 male volunteers recruited from a university population. Subjects were between the ages of 18-35, had no existing cardiorespiratory or musculoskeletal disorders, claimed to be free from consumption of anabolic steroids or any other legal or illegal agents known to increase muscle size currently and for the previous year, and had not performed any regimented resistance training for at least the past year.
Participants were pair-matched according to baseline strength and then randomly assigned to 1 of 2 experimental groups: an internal focus group (INTERNAL) that focused on directly contracting the target muscle during training (n = 15) or an external focus group (EXTERNAL) that focused on the outcome of the lift during training (n = 15). Approval for the study was obtained from the college Institutional Review Board. Informed consent was obtained from all participants prior to beginning the study.
Experimental design
The investigation was carried out over a period of 10 weeks, with 8 weeks dedicated to the RT program and 2 weeks allocated for testing. Pre-study testing was carried out in week 1 and post-study testing was carried out in week 10. A supervised progressive RT was performed between weeks 2-9.
Resistance Training Procedures
The RT protocol consisted of two exercises: Standing barbell curl and machine leg extension. These exercises were chosen because it is easier to direct focus internally during performance of a single-joint movement. Subjects were instructed to refrain from performing any additional resistance-type or high-intensity anaerobic training for the duration of the study.
Training for both routines consisted of 3 weekly sessions performed on non-consecutive days for 8 weeks. All routines were directly supervised by the research team, which included a National Strength and Conditioning Association certified strength and conditioning specialist and certified personal trainers, to ensure proper performance of the respective routines. Subjects performed 4 sets of 8-12 repetitions per exercise. The supervising research staff member provided relevant cues to subjects on each repetition to reinforce the given focus of attention. For INTERNAL, subjects were cued to “squeeze the muscle!” on each repetition; for EXTERNAL, subjects were cued to “get the weight up!” on each repetition. All sets were carried out to the point of momentary concentric muscular failure, operationally defined as the inability to perform another concentric repetition while maintaining proper form. To maintain ecological validity, cadence of repetitions was carried out in a fashion that allowed subjects to best achieve the given attentional focus. Subjects were afforded 2 minutes rest between sets. The loads were adjusted for each exercise as needed on successive sets to ensure that subjects achieved failure in the target repetition range. Attempts were made to progressively increase the loads lifted each week within the confines of maintaining the target repetition range. Prior to training, subjects underwent 10-repetition maximum (RM) testing to determine individual initial training loads for each exercise. The RM testing was consistent with recognized guidelines as established by the National Strength and Conditioning Association (3).
Dietary Adherence
To avoid potential dietary confounding of results, subjects were advised to maintain their customary nutritional regimen and to avoid taking any supplements other than that provided in the course of the study. Dietary adherence was assessed by self-reported 5-day food records using MyFitnessPal.com (http://www.myfitnesspal.com), which were collected twice during the
study: 1 week before the first training session (i.e. baseline) and during the final week of the training protocol. Subjects were instructed on how to properly record all food items and their respective portion sizes consumed for the designated period of interest. Each item of food was individually entered into the program, and the program provided relevant information as to total energy consumption, as well as amount of energy derived from proteins, fats, and carbohydrates for each time period analyzed. To maximize anabolism, subjects were supplied with a supplement on training days containing 25g protein and 1g carbohydrate (Iso100 Hydrolyzed Whey Protein Isolate, Dymatize Nutrition, Dallas, TX). The supplement was consumed within 1 hour post-exercise, as this time frame has been purported to help potentiate increases in muscle protein synthesis following a bout of RT (2).
Measurements
Body Composition and Anthropometry: Participants’ height was measured using a Detecto Physicians Scale (Cardinal Scale Manufacturing Company, Webb City, MO). Assessment of fat mass, fat free mass, segmental body mass, and body water content was carried out using an InBody 770 multi-frequency bioelectrical impedance device (Biospace Co. Ltd., Seoul, Korea) according to the manufacturer’s instructions. Subjects were told to refrain from eating for 12 hours prior to testing, eliminate alcohol consumption for 24 hours, abstain from strenuous exercise for 24 hours, and void immediately before the test. Prior to each measurement, the subject’s palms and soles were cleaned with an electrolyte tissue. Subjects then stood on the InBody 770, placing the soles of their feet on the electrodes. The instrument derived the subject’s body mass, and their age and sex subject were manually entered into the display by the researcher. Subjects then grasped the handles of the unit ensuring that the palm and fingers of each hand made direct contact with the electrodes. Arms were fully extended and
abducted approximately 20 degrees. Analysis of body composition was determined by the unit with subjects remaining as motionless as possible.
Muscle Thickness: Ultrasound imaging was used to obtain measurements of muscle thickness (MT). A trained technician performed all testing using a B-mode ultrasound imaging unit (ECO3, Chison Medical Imaging, Ltd, Jiang Su Province, China). The technician applied a water-soluble transmission gel (Aquasonic 100 Ultrasound Transmission gel, Parker Laboratories Inc., Fairfield, NJ) to each measurement site, and a 5 MHz ultrasound probe was placed parallel to the tissue interface without depressing the skin. When the quality of the image was deemed to be satisfactory, the technician saved the image to hard drive and obtained MT dimensions by measuring the distance from the subcutaneous adipose tissue-muscle interface to the muscle-bone interface, as described previously (1). Measurements were taken on the right side of the body at 3 sites: 1) elbow flexors; 2) mid-thigh 3) lateral thigh. For the anterior upper arm, measurements were taken 60% distal between the lateral epicondyle of the humerus and the acromion process of the scapula; for the mid- and lateral thigh, measurements were taken 50% between the lateral condyle of the femur and greater trochanter for the quadriceps femoris. In an effort to ensure that swelling in the muscles from training did not obscure results, images were obtained 48-72 hours before commencement of the study, as well as after the final training session. This is consistent with research showing that acute increases in muscle thickness return to baseline within 48 hours following a RT session (6). To further ensure accuracy of measurements, 3 images were obtained for each site and then averaged to obtain a final value. The test-retest intraclass correlation coefficient (ICC) from our lab for thickness measurement of the elbow flexors, middle thigh, and lateral thigh are 0.986, 0.972, and 0.997, respectively. The
standard error of the measurement (SEM) for these measures are 0.16, 0.40, and 0.25 mms, respectively.
Isometric Muscle Strength: Strength assessment were carried out using isometric dynamometry testing (Biodex System 4; Biodex Medical Systems, Inc. Shirley, NY, USA). After familiarization with the dynamometer and protocol, subjects were seated in the chair and performed isometric actions of the knee extensors and elbow flexors. All isometric testing was carried out on the subjects dominant limbs. During knee extension trials, subjects sat with their back flush against the seat back pad and maintained a hip joint angle of 85 degrees with the center of the lateral femoral condyle aligned with the axis of rotation of the dynamometer. The dynamometer arm length was adjusted for each subject to allow the shin pad to be secured with straps proximal to the medial malleoli. Subjects were instructed to hold onto handles for stability, and were also strapped in across the ipsilateral thigh, hips, and torso to help prevent extraneous movement during performance. Testing was carried out at a knee joint angle of 70-degrees (4).
During elbow flexion trials, subjects were seated with the right arm flexed to 30-degrees and supported in the saggital plane to eliminate the effects of gravity. The right forearm was strapped into the upper extremity attachment, and the wrist was placed in a supinated position. The hip and knee joint angles were maintained at 85 and 90 degrees, respectively. The left arm was kept pinned to the left side of the trunk with the forearm on the abdomen. Subjects were strapped in by crossover shoulder harnesses and an abdominal belt to help prevent extraneous movement during performance. Testing was carried out at an elbow joint angle of 90-degrees (4).
Each maximum voluntary contraction trial lasted 5 seconds, followed by 30 seconds rest, for a total of 3–4 trials in each position; that is, if a participant’s net joint moment continued to increase in the third trial, then a fourth trial was performed. Participants were verbally
encouraged and were also allowed to view the screen for biofeedback and increased performance (Campenella et al. 2000). The highest peak net extension moment from each of the three trials for each maximum voluntary contraction position was used for analysis.
Isotonic Muscle Strength: Upper and lower body strength was assessed by 6RM testing in the machine knee extension (6RMknee) followed by the barbell elbow flexion (6RMelbow) exercises. Subjects reported to the lab having refrained from any exercise other than activities of daily living for at least 48 hours prior to baseline testing and at least 48 hours prior to testing at the conclusion of the study. Repetition maximum testing was consistent with recognized guidelines as established by the National Strength and Conditioning Association (3). In brief, subjects performed a general warm-up prior to testing that consisted of light cardiovascular exercise lasting approximately 5-10 minutes. A specific warm-up set of the given exercise of 10 repetitions was performed at ~50% of the subject’s 1RM. Subjects then performed sets of 6 repetitions of increasing weight for 6RM determination. Three to 5 minutes of rest were provided between each successive attempt. All 6RM determinations were made within 5 attempts.
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