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Study design and participants
A randomized controlled trial was conducted to investigate the effect of two different concurrent training protocols on physiological parameters and physical performance among healthy middle-aged people over a 13-week period. A total of 33 healthy middle-aged (age = 42.93 ± 8.86 years), were randomly assigned (1:1), using a randomized block design to concurrent training groups: (1) a group that received concurrent training of strength followed by aerobic [SAG, n = 16]; (2) a group that received aerobic followed by Strength training [ASG, n = 17].
Figure 1 displays the study flow diagram. The study inclusion criteria were: (a) being over the age of 40; (b) not having cardiovascular or neuromuscular disorders; (c) not having orthopedic disorders; and (d) not having neurologic disorders. The exclusion criteria consisted of the following: (a) patients with artificial prostheses; (b) individuals who had participated in a structured training program; (c) individuals with symptoms deemed by a medical examiner to be sufficient for exclusion; (d) individuals with diseases that make exercise impossible or require special care (e.g. coronary artery disease, thrombosis, moderate or severe bone disease, and lung or renal disease); and (e) individuals with diseases that require daily use of drugs affecting athletic performance to avoid any influence on fitness measures. After fulfilling the inclusion criteria, participant consent forms were obtained prior to study entry, in accordance with the Helsinki Declaration and subsequent amendments [23]. In addition, all methods and procedures have been approved by Tekirdag Namik Kemal University’s Scientific Research and Publication Ethics Committee granted ethical approval (Protocol No: 2021.275.11.19) and the study was retrospectively registered on clinicaltrials.gov in May of 2023 (clinicaltials.gov identifier: NCT05862415).
Study procedures
This is a parallel group randomized controlled trial study. All measurements were taken over the course of two sessions. During the initial session, the demographics of the subjects were recorded, including age, gender, medical history (chronic health status number), smoking habits, and other characteristics. The seven-day physical activity recall questionnaire (7 Day IPAQ) was utilized to estimate the subjects’ physical activity level. Individuals were categorized as having a moderate level of physical activity if they met any of the following criteria: Engaged in 3 or more days of vigorous-intensity activity and/or walking for at least 30 min per day; or Engaged in 5 or more days of moderate-intensity activity and/or walking for at least 30 min per day; or engaged in 5 or more days of any combination of walking, moderate-intensity, or vigorous-intensity activities, achieving a minimum total physical activity of at least 600 MET-minutes per week. Before starting with the training protocols, all anthropometric measurements were taken, and physical tests were conducted. The testing sessions were conducted with a 72-hour interval between the start of the program and baseline assessment. In the initial visit, participants filled out a questionnaire where they provided demographic details and completed the 7-Day IPAQ short form. After this, a series of evaluations were conducted, which included measurements of body anthropometric measures and grip strength tests, followed by the 1RM strength assessments. In the second visit, participants underwent spirometric tests and a 1-mile run-walk test. All tests were conducted at the same time of day, between 17:30 and 19:30, to control for the impact of circadian rhythms. The following testing procedures were implemented:
Body composition assessment
Height (m) was measured using a Mesilife 13,539 brand portable stadiometer with accuracy of 0.1 cm. A stabile eight-polar tactile electrode bioelectrical impedance analyzer (Tarti Fast, Japan) was used to measure body mass (kg), fat percentage, and skeletal muscle mass (kg). This bioelectrical impedance analyzer’s validity has previously been reported [24]. Body mass index (BMI) (kg/m2) = was calculated by dividing body mass (kg) by body height squared (m2).
Physical activity level
The short form of International Physical Activity Questionnaire (IPAQ) was used to assess the physical activity status [25]. The questionnaire inquired about the duration and frequency individuals allocate to vigorous-intensity exercise, moderate exercise, walking, and sitting during the day. The metabolic equivalents (i.e., METs/week) related to vigorous PA, moderate-intensity PA, and walking, and total time of PA performed were calculated using guidelines for data analysis [26].
Predicated maximal oxygen uptake (VO2max)
1-mile walk-run performance test was used. The aim of this test is to cover a distance of one mile in the shortest possible time. Participants can alternate between walking and running as desired; however, they should be encouraged to cover the distance as quickly as feasible. The time elapsed to cover a mile distance, measured in minutes and seconds. During the testing and recovery, the heart rate of the participants was monitored with a heart rate sensor (Polar Verity Sense; Kempele, Finland). Polar Verity Sense can be connected to a sports watch or app via Bluetooth®, ANT+, and internal memory to instantly track your training or view the data after training. As a result, the participant’s time for completing the 1-mile test was tracked using a smart phone GPS system. The validity of the device has been reported previously [27]. The participants VO2max values were calculated using the formulas below:
Male (VO2max) = 108.844 – 0.1636W – 1.438T – 0.1928 H
Female (VO2max) = 100.5 – 0.1636W – 1.438T – 0.1928 H
W = Weight in kg, T = Time for the one-mile run and H = Heart rate at the end of the run [28].
Dynamic respiratory parameters
All spirometry measurements were taken in accordance American Thoracic Society (ATS) and European Respiratory Society (ERS) [29]. We used a spirometer device (Minispir®, PC-based Spirometer with Oximetry option, Italy) to take measurements from the participants. Participants were instructed to hold and sealed the lip around the mouthpiece then breathe normally twice and then exhale the maximally filled lungs with a maximal breath through the mouthpiece orifice. Each test was repeated twice, and the best results were recorded for each participant. We measured the Forced Vital Capacity (FVC), Forced Expiratory Volume in One Second (FEV1), and Peak Expiratory Flow in this procedure (PEF).
Grip strength
A handgrip dynamometer was used to measure the strength of the hand and forearm muscles (in kilograms) (Tanita Handgrip Meter, RM40, East Malaysia). The test was carried out with the elbow fully extended and the forearm in a neutral position. At 1-minute intervals, three measurements were taken on the subjects’ dominant side. The participants were instructed to told the handgrip of the device tightly for 3 s [30]. For statistical analysis, the highest scores from three measurements were taken.
1-repetition maximum strength test
The 1 repetition maximum (1RM) test, an indirect and simple test, can be effectively and safely administered. It is feasible to calculate the 1RM value using the calculations based on the maximum repetition limit between 2 and 20 for any weight. In order to determine the 1RM values of the study participants, indirect 1RM bench press, leg press, long pulley, leg extension, and overhead press were used. 1RM tests were performed using a weight machine (Technogym Selection 900). The formula for calculating 1RM indirectly is given below [31].
1RM= (Lifted Weight) / [1.0278 ? (Repetition*0.0278)]
Training program
Training sessions were conducted twice a week for 13 weeks, either indoors or outdoors at an athletic field pavilion. Each session started with a 5- to 7-minute warm-up, consisting of low-intensity walking and running, and dynamic mobility exercises. Active recovery of 4- to 5-minute was based on stretching and relaxation exercises. Sessions lasted approximately 50 min (warm-up and cold down included). A detailed description of the 13-week training program is reported in Fig. 2.
An illustrative scheme of training program across groups
All training sessions were supervised by 8 experienced personal trainers. Paired groups were formed according to the similarity between the strength and aerobic fitness levels of the participants. The circular training method was used in the resistance training phase. During the aerobic training phase, a series of movements from moderate intensity to vigorous intensity was performed. The step loading periodization principle was taken into account in both resistance training and aerobic exercises.
The RT lasted approximately 20–25 min per session and included two sets of 8–20 repetitions, with a rest interval of 1–2 min [32]. The assessing of the Repetition Maximum (RM) involves opting for a range of RM targets. Subsequently, participants execute each exercise with varying levels of resistance until they achieve the predetermined RM goal. The resistance training program was performed using the circuit training method in which two or three sets were performed. Intensity was measured with the Borg CR-10 scale [33], initially starting at 2 points and progressively increasing to five points weekly as described in Table 1. The RT exercises included: squat, barbell bent-over row, overhead press, plank, lateral pull down, triceps push down, barbell curl, leg extension, leg curl, lunge, barbell bench press, crunches etc. Especially in the first 4th weeks of the training protocol, it was preferred to use hydraulic and roller system fitness machines in resistance exercises. After the 5th week, free weights such as dumbbells and barbells were started to be used as the exercise loads progressed. All the training sessions were supervised by researcher who conducted the exercise sessions and assured the safety and the correct execution of the movement.
Aerobic exercise training was designed to include different aerobic training protocols. Intensity was established between 50 and 65% and 80–85% of HRmax for both groups (SAG and ASG). The HRmax was estimated using Tanaka et al. [34] equation (i.e. (208 – age) ∗ 0.7). The heart rate variables of the participants during aerobic exercise were determined using the heart rate sensor. In line with the step loading periodization principle; an aerobic training program was designed from moderate to vigorous intensity, with HRmax varying between 50 and 85% from the 1st week to the 13th week of the participants. The aerobic training program lasted approximately 20–25 min. Aerobic training includes walking and running periods and was carried out on a 400 m outdoor track. In periodization, especially 1st-4th. walking, jogging and running-based exercises were preferred between weeks. In the following weeks, in addition to these exercises, more intense exercises were added to the training program (rope jumping, jumping jack, burpee, vertical jumping, broad jumping, sliding, footwork etc.). The training strategy was the same in both groups.
In SAG, the order of exercises began with strength training followed by aerobic training, whereas in ASG, aerobic training was conducted before engaging in strength training. Figure 2 highlights the discrepancy in the exercise order between the two groups.
Statistical analyses
The data were analysed with the statistical program SPSS v.18.0 for Windows (SPSS Inc., Chicago, USA), and the significance level was set at p < 0.05. Before conducting any analysis, all data were checked for normality using the Shapiro-Wilk test and homogeneity with the Levene’s test, respectively. Descriptive statistics are presented as mean and standard deviation (SD). The chi-square test and the independent t-test were used to compare sociodemographic variables between the groups. A repeated measures 2 × 2 analysis of variance (ANOVA) (group x measurement) was conducted. Before performing ANOVA, the necessary conditions for analysis were checked. Box’s Test of Equality of Covariance Matrices was used to evaluate whether there were any significant differences in the covariances between the measurement groups for pairwise combinations of the groups. In addition, the magnitudes of the differences between values were interpreted using the partial eta squared effect size. The partial eta squared coefficient (ηp2) was presented as it indicates how much of the variance of the dependent variable is explained by the independent variable [35].
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