Experimental Approach to the Problem

To determine which method, compound or traditional sets, was more effective in improving the aforementioned variables of interest, recreationally active females were pair matched for training groups based on body mass index and randomly assigned to: compound set (n = 10), traditional set (n = 12), or a control group that did not train (n = 10). All resistance training included lower body exercises performed with a full range of motion and proper technique, which was monitored and supervised for each subject. All testing measures were taken pre- and post-training following familiarization. Strength and endurance tests were completed on separate days for squat and leg press, in a random order, and were separated by 72 h of rest. Ultrasound measures were taken at the start of training and 1 week after the completion of training to reduce the influence of muscle swelling on changes in size. Supervised training sessions occurred twice weekly and were separated by 3 days. Compound and traditional set training groups were matched for duration, relative intensity, volume, and cumulative rest. Each group performed a 5-min standardized warm-up, Smith Machine squat, and 45° leg press, in the order given. The compound set group performed the squat and leg press with no rest between exercises, aside from switching machines, which was considered one set. The rest between compound sets was 150 s for three sets and 140 s when four sets were completed. The traditional set group performed the prescribed sets of squats with 1 min rest between sets, rested for another minute and then performed the leg press with 1 min of rest between sets. The cumulative rest for each group was 5 min before the completion of the last set. Both training groups performed three sets for the first 7 weeks and four sets for the last 5 weeks, for each exercise. The full testing and training schedule are displayed in Table 1.

Table 1 Training schedule (2 days per week), displayed as sets × repetitions at load Full size table

Subjects

Thirty-one females (mean ± SD; 21 ± 2 years), who were not currently following a prescribed resistance training program, were recruited for the study. All subjects reported being recreationally active, which consisted of participation in a variety of physical activities such as occasional aerobic or resistance exercises (1–2 times per week combined maximal), club sports, yoga, and pilates classes. Subjects had to attend 22 of the 24 training sessions to be included, which led to the removal of two subjects from the compound set group due to personal reasons unrelated to the training. After thorough explanation of what the study entailed, subjects were asked to sign an informed consent and complete a health history questionnaire. Those who were pregnant, at risk of injury due to cardiovascular, metabolic, pulmonary or musculoskeletal problems, as determined from their health history questionnaire or a prior medical examination, or did not satisfactorily pass joint integrity tests performed by a licensed athletic trainer, were excluded from the study. Exclusion criteria also ensured all subjects were healthy nonsmokers, regularly menstruating, free from disease or debilitating conditions, and non-drug or steroid users. Markedly overweight with a body mass index (BMI) greater than 27, underweight (BMI less than 19), and hypertensive individuals (blood pressure greater than 140 mmHg systolic and 90 mmHg diastolic) were also excluded from the study. It was requested that subjects refrained from any additional resistance training and supplement use during the study, as well as maintenance of normal dietary habits. These parameters were approved by the University Institutional Review Board.

Familiarization

Prior to beginning training, all subjects completed an orientation to ensure safety and diminish any learning effect on training, as subjects had little experience with the exercises. During orientation, each subject accumulated at least 3 h in the weight room becoming familiarized with the Smith Machine squat and 45° seated leg press. Subjects were required to perform satisfactory lifts for each exercise, evaluated by a certified strength and conditioning specialist (NSCA–CSCS). After multiple lifts were deemed acceptable, controls were set for range of motion. For the squat, elastic bands were set between the Smith Machine supports and positioned, so the end of the barbell made contact with the bands when the subject’s thighs were parallel to the floor. For the leg press, each subject held a flexed position (90°) to record depth level, which was marked on the leg press rails. Elastic band height and leg press depth level were recorded for each subject and used for all training.

Muscular Strength and Endurance

Following familiarization, muscle strength and endurance testing was performed on separate sessions for the squat and leg press with a rest of 72 h. Each subject completed a 5-min standardized warm-up on a cycle ergometer prior to testing. For strength testing, a one-repetition maximum (1-RM) was performed with identical procedures for each subject and exercise. All pre-maximum sets were based on percentages of self-estimated 1-RM and performed in the following order: 8–10 repetitions at 40–60% 1-RM, rest 2–3 min, 3–5 repetitions at 75% 1-RM, rest 3–5 min, and 1–3 repetitions at 80–90% 1-RM. Then the subject was allotted 4–5 min of rest before a 1-RM attempt. If a lift attempt failed, the weight was decreased before a second 1-RM attempt was made after 5 min of rest. If the lift was successful, 4–5 min of rest was given and another 1-RM was attempted with increased weight. This method was repeated as necessary until a lift failed more than once. Attempts completed within the approved range of motion for each subject and exercise were deemed successful. Absolute and relative (load lifted divided by body mass) strength values were analyzed and reported.

After each 1-RM was ascertained, 15 min of rest was provided to prepare for repetitions to fatigue. The intensity was adjusted to 60% of each subject’s recorded 1-RM on both exercises and the subjects executed as many repetitions as possible. Repetitions were counted only if proper form and range of motion were maintained. Subjects were informed that a pause for longer than 3 s after completion of a repetition or a significant loss of form would conclude the test. The total number of repetitions performed served as the measure for absolute muscular endurance [25]. The same load used in pre-testing was used for post-testing to evaluate improvements in absolute muscle endurance after 12 weeks of training.

Muscle Size and Architecture

Muscle thickness, CSA, and PA were estimated via ultrasound of the vastus lateralis. The study utilized two-dimensional B-mode ultrasound imaging (eSaote BioSound MyLab 25, Biosound Esaote, Inc., Indianapolis, IN, USA) with a 5-cm linear transducer (frequency, 7.5 MHz; axial resolution < 0.5 mm). Settings for sonographs were standardized with a depth of 5 cm and gain of 52. Direct measurement of muscle thickness, PA, and estimations of CSA were attained from sonographs, by using reflected echoes that delineate muscle structures (skin and adipose tissue, muscle fascicles, aponeuroses, and bone) for measurement. Digitizing software (Scion Image for Windows, http://www.scioncorp.com) allowed researchers to import the sonographs, find landmarks, and make measurements.

The vastus lateralis muscle of the right leg was measured with the subjects lying supine, with their upper legs elevated and relaxed, and knees slightly flexed (35°–45°). To improve transducer communication and reduce the chance of touching skin, a water-soluble conductor gel was placed on the site of measurement. For CSA, double-sided tape guided the transducer as it scanned the entire segment (distal) taking multiple pictures from every angle of the vastus lateralis, which were then superimposed to create a cross-sectional model of the muscle. The transducer was then placed perpendicular to the skin and parallel to the muscle fascicles. Muscle thickness and pennation angle were taken at 50% (proximal) and 25% (distal) of thigh length (distance from the proximal patella to the anterior superior iliac spine), respectively. Multiple measurements were taken at each site. Muscle thickness was calculated as the mean of the distances between the superficial and deep aponeuroses at the ends and center of each 5 cm-wide sonograph. Pennation angles were defined as angles between the echoes of deep aponeurosis and interspaces among the fascicle. The average value of two measurements was used for CSA, muscle thickness, and PA.

Workout Time and Soreness

Workout time was monitored by supervisors via stop watches and recorded for each session. The time clock started when contact was made with the Smith Machine barbell after completion of the warm-up, and ended when the last repetition of the final leg press set was completed. Rest periods between sets were monitored similarly. Subjects were cued to prepare for the next set approximately 15 s before it began.

A soreness scale [29] was provided to subjects so they could subjectively provide their post-workout soreness rating for 2 days following each session. This allowed for potential identification of differences between compound set and traditional set for sensation of delayed onset of muscle soreness and/or post-exercise pain.

Statistical Analysis

Statistical analyses were performed using SPSS 24.0 for Windows (SPSS Inc., Chicago, IL, USA). Data were normal and screened for outliers, which were removed from analysis if greater than 2.5 standard deviations from the group mean. Mixed model (between/within) analysis of covariance (ANCOVA) tests were used to determine differences between or within groups, pre-training and post-training for all variables. Although the baseline measurements were no different between groups, the use of ANCOVA may help account for ceiling or floor effects in detecting changes over time [30]. Significance was bound by α level of P < 0.05. In the case of significant effects, pairwise comparisons were used with Bonferroni adjustments. The reliability of ultrasound measurements was found by calculating the intraclass correlation coefficient (ICC) for all images from the two sites. The ICCs were as follows: muscle thickness, 0.92 at proximal and 0.89 at distal; PA, 0.91 at proximal and 0.88 at distal; CSA, 0.97. T test was used to compare training time between groups and the nonparametric L statistic was used to compare subjective soreness between groups post-workout. Effect sizes were calculated using Cohen’s d and were defined as small, d = 0.20–0.49; moderate, d = 0.50–0.79; and large, d ≥ 0.80 [7]. In addition to statistical analysis and effect sizes, the number of subjects who exceeded the minimal difference needed to be considered before a real change in pre- to post-test was considered for muscle CSA and thickness.