Performing resistance training (RT) on a regular basis provides a safe and effective method to increase muscular strength, local muscular endurance, fat free mass, as well as overall physical function [1
]. This increase in physical function has been related to improved body coordination [2
], whereas impaired functional ability (i.e., the ability to perform activities of daily living) may lead to higher injury prevalence [3
For novices, RT frequency is recommended to be two to three nonconsecutive days per week [1
]. The American College of Sports Medicine (ACSM) also states that: ”The choice to incorporate free weights or machines should be based on level of training status and familiarity with specific exercise movements as well as the primary training objective” [5
]. Machines are training devices that have pin loaded weight stacks with fixed lever arms and range of motion. They provide a safer use than free weights and can be used relatively easy without supervision under any circumstances [6
]. In contrast, free weights, including dumbbells, barbells, kettlebells, cables, etc., allow free movement and thus need to be stabilized by the executioner himself [6
Because of leading to a higher inter- and intramuscular coordination, free weight RT exercises may result in a better overall body coordination and are generally considered to be more functional compared to using machines for RT [5
]. Accordingly, free weight exercises provide a higher neuromotor stimulus as shown in electromyography (EMG) studies [7
]. For example, unstable squats result in higher EMG activity in synergistic muscles [7
], and EMG activity is also found to be higher in the medial deltoid muscle during a free weight bench press as compared to the more stable Smith or chest press machine alternative [8
]. In addition, a recent study by Schott et al. (2019) observed that the relative increase in exercise load from baseline was higher in older adults training with free weights as compared to those using the machine alternative, but only for the triceps brachialis and knee and hip extensor muscles [10
]. Also, Rossi et al. (2018) concluded that free weight squat training elicited better strength outcomes than training with the leg press machine, whilst balance improved equally regardless of the exercise used [11
]. In contrast, Schwartz et al. (2019) observed a higher increase in peak jump power in recreationally active women training on the machine squat as compared to peers performing free weight squat training, whilst similar improvements in agility and sprint performances were observed in both training groups [12
]. A higher activation and recruitment of more muscle mass when using free weights should increase testosterone levels to a greater extent [13
], and thus induce more hypertrophic effects [14
]. However, a possible disadvantage of using free weights might be the (lack of) necessary experience to perform certain exercise movements correctly, since poor technical skills and inferior movement patterns might increase injury risk [15
]. Therefore, free weight exercises are typically not recommended for novices, but are often only introduced when some level of RT experience is attained [5
The training principle of specificity is a well-accepted concept of transfer in motor learning [16
], indicating that improvements in performance are specific to the exercise and equipment being used. Boyer (1990) already demonstrated this training specificity in the context of RT a few decades ago [17
]. Essentially, one can expect that training with machines will result in greater improvements in machine strength test outcomes compared to using other types of testing equipment. The same principle applies when training with free weights, even when the same muscles and muscle groups are used in both types of RT exercises. However, training with free weights has been suggested to produce a more effective learning transfer than training with machines [18
]. Therefore, with regard to changing from using machines to free weights for RT purposes, a stagnation or fallback in performance progression may be possible because the practitioner needs to acquire a new motor program before the desired load can be applied. To date, however, no evidence is available to support this particular hypothesis.
The few existing studies that compare the effect of different RT modes on anthropometric and performance parameters have shown conflicting results. Furthermore, there is a paucity of studies on novice practitioners and, thus far, no research exists in which the influence of RT equipment on the learning transfer to the opposite training mode (i.e., using machines vs. free weights) is examined in novices. Therefore, the primary purpose of the present randomized parallel trial was to compare changes in anthropometric estimations of muscle size, strength and functional ability in novice male adults when participating in a 10-week whole-body RT program using either machines only, free weights only, or when changing halfway the program from using machines to free weights. Previous research leads to the hypothesis that participants using free weights only during the RT program will show a greater gain in muscularity, strength, and functional ability as compared to those using machines only. A secondary purpose was to investigate the bidirectional learning transfer in terms of strength and functional ability gains between using machines and free weights. It was hypothesized that a greater positive learning transfer will be observed to strength testing with machines when training with free weights as compared to strength testing with free weights when training with machines.
The main finding from this randomized parallel trial is that male adults being novice in RT showed significant increases in anthropometric estimations of muscle size, strength, and functional ability, regardless of using machines (M) versus free weights (FW) or the combination thereof. Secondly, an equally positive transfer in strength gains was observed between training with M and with FW in both directions (i.e., from training with M to testing with FW as well as from training with FW to testing with M). Our findings do not support the hypothesis that RT with FW would elicit better training effects in terms of muscularity, strength, and functional ability, nor did it result in a better learning transfer in performance on machines as compared to the opposite direction.
In the present study, significant increases in upper arm, thigh, and chest circumferences were found for all RT groups when comparing pre-, mid-, and post-intervention outcomes over the 10-week RT program applied. This positive change over time in these anthropometric estimations of muscle size is an expected result as a 10-week RT program should be sufficiently long to induce hypertrophic effects in the untrained [19
]. Seynnes et al. (2006) observed that changes in muscle size were already detectable after three weeks of RT in recreationally active young healthy males [19
]. Interestingly, in the study of Moro et al. (2020) hypertrophic effects were only observed in recreationally active men who engaged in 8 weeks of high intensity interval RT but not in their peers performing traditional RT [31
]. Muscular adaptation and the role of fitness level, training volume, intensity, and periodization are indeed topics that can further be explored [32
For the novice individual, it is known that strength gains experienced over the first 5–8 weeks of RT are primarily neurological in nature, while gains experienced over the following weeks and years result from muscular hypertrophy [33
]. In the present study, participants already demonstrated significant increases over the first five weeks in upper arm and chest circumferences as well as a similar trend towards a larger thigh circumference. Since waist circumference did not significantly change during the 10-week RT program, it can be cautiously assumed that the observed significant changes in limb and chest circumferences may be mainly attributed to an increase in muscle size instead of adipose tissue [24
It was hypothesized that the muscular strength in RT group of participants using FW only would improve significantly more than in their counterparts using M only during the 10-week RT program since more muscle fibers and synergistic muscles are activated to maintain postural balance and stabilization during the FW exercises [7
]. This statement was previously confirmed by the study of Schott et al. (2019) conducted in older adults (>60 years old, mixed gender) based on more pronounced relative strength increases in some muscle groups, but not all, after 26 weeks from baseline when using FW for RT (i.e., 50% in leg press versus up to 120% in squat) versus when using M [10
]. However, people at a more advanced age may initially feel uncertain when performing unfamiliar exercises that challenge their postural stability, possibly resulting in an underestimation of strength at baseline when being tested with FW. The results of the present study, however, demonstrate that RT novice adult males can achieve equal strength gains using either FW, M, or a combination of both (starting with M). In other words, the strength gains in all of our participants were found to be similar irrespective of the RT equipment being used during the 10-week program. Regardless of RT group, participants’ mean estimated 1-RM improved with 27% up to 43% from pre- to post-intervention depending on the targeted muscle groups. Similar gains in strength performance were observed by Rossi et al. (2018), who compared three groups (i.e., leg press-only group, squat only group, combined squat and leg press group) and found that squat training was significantly better in comparison to both other training groups [11
]. However, an important difference compared to the present study to consider is that in the study of Rossi et al. (2018) only the leg press and/or squat were trained, targeting the knee and hip extensors as primary movers, and that a different training volume was administered (6 sets of squat or leg press vs. 3 sets of each exercise in the present study). Apart from all specific M and/or FW exercises, this finding of equal (functional) strength gains in each group was also confirmed for the SBJ as a neutral test. Also, Schwartz et al. (2019) observed that vertical jump height improved equally in young recreationally active women after 6 weeks of free weight squat versus machine squat training, as was also the case for agility and 30 m sprint performance [12
]. However, women who trained with the machine squat did produce a higher peak power output during vertical jumping as compared to their counterparts who trained with free weights [12
]. Thus, Schwartz et al. (2019) concluded that machine training can elicit equal or even superior training effects. Our study involving a 10 week RT program in male novices confirms that strength can equally increase regardless of the training mode.
The lack of significant interaction effects for the 1-RM estimations in the present study shows that there is an equal strength transfer from one RT mode to the other. This means that changing equipment is not necessarily accompanied with a delayed progression in muscularity, strength or functional ability, at least not in novice male RT practitioners. This rather surprising finding does not support the earlier mentioned concept of training specificity, but demonstrates that there was a positive transfer of strength both from M to FW and from FW to M in the present study. Despite the advantages of FW in terms of intermuscular coordination and activation of synergistic muscles [7
], no difference in learning transfer was found. This unexpected finding might be due to the testing load of 10-12-RM (corresponding with ~75% of 1-RM) that could have limited the stability role of synergistic muscles, as was also suggested by Schick et al. (2010) and McCaw and Friday (1994) [8
]. Schick et al. observed a higher recruitment of the stabilizing rear and medial deltoid muscles during free weight bench press as compared to the stable Smith machine alternative, but only when performed at 60% of 1-RM and not at 90% of 1-RM. They assumed that while using lighter loads, the lower activity of the agonist muscles decreases joint stiffness and in turn increases the stabilizing role of synergistic muscles [8
]. Thus, other findings may be observed when applying a lower training or testing intensity or when training effects are evaluated after a longer training period [28
]. Future studies should thus provide more insight in this respect.
It is also known that RT enhances one’s body coordination [2
], which should lead to an improved functional ability. Our hypothesis that FW exercises would result in a better coordination for real life movements and thus being more functional than a M only RT program was not confirmed as shown by equal improvements in total FMS score over time in all three RT groups. The study of Rossi et al. (2018) showed similar results, using the Star Excursion Balance Test to assess balance in participants training with M only, FW only, or both [11
]. Balance improved equally in all three groups over the course of that 10-week study [11
]. Despite the difference in assessment tools being used, it seems that M and FW, or a combination of both (with M preceding FW in our study) can elicit an improved functional ability and a better quality of movement patterns. An increase in strength may be a factor that resulted in a better overall score on the FMS in each group, as some components in this test battery rely on muscle strength, such as the deep squat and the trunk stability push-up. Another part of the explanation may be the occurrence of a learning effect, regardless of the RT program.
There are several aspects of the present study that should be taken into account when interpreting its findings. First, our study deliberately included only men who were novice in RT and recruited by means of convenience sampling. Therefore, caution is warranted when generalizing and extrapolating the presented study findings, more specifically with regard to women and individuals who are already more familiar with RT. Secondly, we used body segment circumferences as a field-based method to estimate the evolution in muscularity. Besides its clear advantages—such as being low in cost, very easy to apply, and non-invasive—one disadvantage of using these anthropometric estimations to assess changes in muscle size is that they do not correct for changes in fat mass. Therefore, our study participants’ waist circumference was also considered to control for any changes in overall fat mass, and thus body fat percentage, since men tend to store their excess fat primarily in the abdominal region [24
]. Another disadvantage of using segmental anthropometrics is the lower sensitivity and possible disturbing effects of hydration as compared to total and/or segmental body composition assessments using laboratory techniques such as dual energy X-ray absorptiometry [35
]. Therefore, possible subtle inter-group differences in body composition may not have been detected. Finally, the present study design did not allow to control for possible learning effects on the strength tests nor the FMS. It can be assumed that these would have been equal for each RT group, possibly contributing to the equal learning transfer and progressions in strength observed in this study.
Nevertheless, some specific strengths of the present study can be highlighted as well. First, this study, including three test occasions, used a sufficiently high predefined power which lowers the chance on the probability of false negative results. Secondly, participants were randomly assigned to one of the three different RT groups. The present study also applied international recommendations for RT in novices, such as using a whole-body workout instead of focusing on a single muscle or muscle group and also in terms of training load as well as concerning the timing and magnitude of increasing intensity. Furthermore, we used a realistic and feasible setting with exercises that are relatively easy to acquire for novices. Finally, this study applied a holistic approach including anthropometrics, strength, as well as functional ability outcomes to evaluate RT effects, whilst its particular design allowed to investigate the learning transfer between RT modes offering new insights for novices in RT.