By Quanthlete
A systematic review and meta-analysis, published in BMC Sports Science, Medicine and Rehabilitation, investigates the effectiveness of free-weight versus machine-based strength training on maximal strength, muscle hypertrophy, and jump performance. Conducted by Haugen and colleagues, this study compiles data from 13 studies, with a sample size of 1016 participants, aiming to provide evidence-based insights for trainers, athletes, and fitness enthusiasts on which method yields optimal training outcomes.
Background
The debate between free-weight and machine-based strength training is longstanding. Free-weights, such as dumbbells and barbells, are thought to promote greater functional strength by activating stabilizing muscles, while machines offer guided, controlled movements that may be safer for beginners.
Methods
Following PRISMA guidelines, the study included adults aged 18–60, undergoing at least six weeks of strength training with either free-weights or machines. The effects on maximal strength, muscle hypertrophy, and jump performance were measured using metrics like one-repetition maximum (1RM) and countermovement jump (CMJ) height.
Key Findings
- Maximal Strength:
- Free-Weight Exercises: In tests measuring maximal strength using free-weight exercises (like squats or bench presses), participants who trained with free-weights showed significantly greater gains compared to those who used machines. The standardized mean difference (SMD) was -0.210 (95% CI: -0.391 to -0.029, PI: -0.484 to 0.064, p-value = 0.023)(s13102-023-00713-4).
- Explanation: The negative SMD indicates that free-weight training had a stronger impact on strength gains when tested using free-weight exercises. The relatively low p-value (< 0.05) supports that this result is statistically significant, suggesting that free-weights allow for more strength adaptations, likely due to the activation of stabilizing muscles and engagement of multiple muscle groups. This supports the principle of specificity, where training in the same mode as testing yields better outcomes.
- Machine Exercises: For machine-based strength tests, machine training showed a slight advantage, with an SMD of 0.291 (95% CI: -0.017 to 0.600, PI: -0.147 to 0.729, p = 0.064)(s13102-023-00713-4). Although this result suggests that machine-based training was more effective when tested on machine exercises, the p-value (> 0.05) indicates that this difference was not statistically significant.
- Explanation: The findings highlight that, although machine training might improve strength on machine-based tests, it may not translate well to free-weight tasks. This outcome further supports that specific adaptations occur in the mode of training. While machine exercises may not demand the stabilization required in free-weight exercises, they allow for isolated muscle focus, which may explain the improvement on machine-based tests.
- Hypertrophy:
- The analysis found no significant difference in muscle hypertrophy between free-weight and machine-based training. The SMD was -0.055 (95% CI: -0.397 to 0.287, PI: -0.611 to 0.500, p = 0.751)(s13102-023-00713-4).
- Explanation: With an SMD near zero and a high p-value (p > 0.05), the findings suggest that both training modalities are equally effective in promoting muscle growth. This is likely because hypertrophy depends on factors like load, volume, and time under tension rather than the type of equipment. Free-weights activate stabilizing muscles, potentially benefiting overall muscle balance, while machines may allow for a more focused activation of target muscles. For hypertrophy goals, combining both free-weight and machine exercises could optimize results by engaging both primary and stabilizing muscle groups.
- Jump Performance:
- Jump performance, assessed through countermovement jump (CMJ) height, showed no significant advantage for either training modality. The SMD was -0.209 (95% CI: -0.597 to 0.179, PI: -1.208 to 0.790, p = 0.290)(s13102-023-00713-4).
- Explanation: Jump performance is often used as a measure of explosive lower-body strength, particularly useful in sports performance contexts. Since neither free-weight nor machine-based training directly targets explosive power, it’s unsurprising that both methods showed similar results. The wide prediction interval suggests high variability, meaning some individuals may benefit more from one type of training than another, but overall, neither is superior. To specifically improve jump performance, incorporating plyometric or explosive training may be more effective than solely relying on traditional resistance training.
Practical Applications and Recommendations
The results highlight that the principle of specificity applies to strength training modality: to gain maximal strength in a specific exercise, one should train using that exercise. Free-weights are recommended for athletes who seek functional strength gains or are preparing for sport-specific movements, while machines may benefit beginners seeking controlled, isolated strength gains without high injury risk.
Conclusion
The study suggests that neither free-weight nor machine-based training holds a universal advantage across all outcomes. Trainers and athletes should tailor their approach based on individual goals, with the understanding that each method offers unique benefits suited to different training needs.
References:
- Haugen, M. E., Vårvik, F. T., Larsen, S., Haugen, A. S., van den Tillaar, R., & Bjørnsen, T. (2023). Effect of free-weight vs. machine-based strength training on maximal strength, hypertrophy and jump performance – a systematic review and meta-analysis. BMC Sports Science, Medicine and Rehabilitation, 15(103).