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Ozaki et al. [1] recently introduced ‘stepwise load reduction training’ (SLRT). In SLRT, an individual starts an exercise set with a heavy load, performs as many repetitions as possible at that load, then proceeds to do additional sets with lighter loads in a stepwise manner [1]. According to the authors, SLRT differs from traditional drop set training, because in traditional training, the initial load is not necessarily maximal or near maximal [1]. The authors argued that SLRT is a time-efficient training method that might result in “a broad range of adaptations” (i.e., concomitant increases in muscle strength, muscle endurance, maximal anaerobic power, anaerobic capacity, and VO2max) [1]. They acknowledge research is needed to test their hypothesis [1]. We think that SLRT is interesting, but it could be accomplished more effectively and efficiently with a connected adaptive resistance exercise (CARE) device. The aim of the current letter is to argue that, to the extent SLRT might be an effective training method, CARE devices work well for the SLRT concept.
Traditional resistance training equipment, such as free weights (e.g., dumbbells, barbells), weight stack machines, and elastic bands, can provide adequate stimuli for increasing muscle strength [2,3,4,5,6,7]. However, such equipment has limitations. First, the load cannot be altered after the set has commenced (i.e., no load alterations between repetitions). When an individual fails to lift a load due to fatigue, they must stop and select a lighter load to complete more repetitions. Practical inconveniences exist for removing weight plates or selecting lighter dumbbells to achieve the stepwise load reductions associated with SLRT during an exercise session. Second, with traditional resistance training equipment, the same load is used for both the concentric and eccentric phases. However, eccentric strength is significantly greater than concentric strength [8,9,10,11,12,13,14]. Moreover, concentric fatigue occurs quicker than eccentric fatigue [8, 9, 12]. Thus, traditional equipment might not optimize the intensity for eccentric contractions. Eccentric exercise at a given load is also perceived as less effortful and demands less oxygen [15, 16]. Thus, eccentric exercise might be more appropriate for patients with heart and/or respiratory diseases or older adults with less tolerance to exercise [17, 18].
CARE devices are new resistance training equipment that have the potential to overcome limitations of existing equipment. CARE devices, which might also be called ‘connected strength trainers’, ‘smart trainers’, or ‘digital weights’, consist of a load-generating mechanism controlled by firmware that monitors user kinetics and kinematics and adjusts (‘adaptive’) the load-generating mechanism accordingly via wireless technologies (‘connected’).
CARE devices are well suited for SLRT (Figs. 1, 2, 3). CARE devices can adapt resistances within and between repetitions. Before the set begins, users can select a resistance that permits maximal or near maximal eccentric contractions, with the understanding the CARE device will reduce the resistance in the concentric phase to match the force-generating capacity of the muscle. Moreover, CARE devices can reduce resistances within a set as a user loses force-generating capacity due to fatigue. Thus, a user can perform a high number of repetitions without having to stop to reduce loads.
In Figs. 1, 2, we present data from use of a CARE device (V-Form Trainer, Vitruvian, Perth, Australia) to achieve 25 consecutive maximal concentric and eccentric contractions (CONmax–ECCmax) for unilateral biceps curls. Prior to the set, the user, via the device’s mobile phone application, indicated he wanted to perform 25 repetitions with a resistance equal to his eccentric maximal strength on the device. In the set, the user never experienced this resistance in the concentric phase because the device adapted the resistance to the user’s force-generating capacity during the concentric phase. From repetition 2 to 25, average concentric and eccentric phase forces decreased by 77.9% and 55.3%, respectively. As the user fatigued, the CARE device reduced the resistance so the user could continue to exercise at 100% of maximal momentary effort. Reduced neural drive in later repetitions was observed for biceps brachii and anterior deltoid (Fig. 2)—a finding consistent with previous work on fatigue from repeated maximal contractions [8, 12]. The 25 repetitions were completed in 147 s without rest. This is longer than the ~ 120 s needed to complete the protocol described by Ozaki et al. [19], which involved ~ 35 repetitions over five dumbbell sets in SLRT. However, the five dumbbell loads were prepared in advance by test administrators and do not reflect time required to complete the protocol outside of a laboratory.
A key difference between SLRT with free weights and the CARE device used in this example is the CARE device permitted maximal effort at every moment (Fig. 3). With free weight-based SLRT, the individual works submaximally at a given load until the repetition that causes failure. Conversely, the CARE device in this example gives the user the opportunity to perform SLRT with resistances that are maximal or near maximal at every moment based on joint angle, lift phase, and fatigue. Submaximal resistances can also be used with CARE devices.
In sum, CARE devices utilize adaptable resistances. They have the potential to overcome limitations of traditional resistance training equipment. They can provide different resistances within a given repetition based on joint angle and movement phase (concentric, eccentric) and between repetitions as fatigue occurs. CARE devices also make it possible to perform a repetition composed of multiple exercises because the resistance adapts to user force-generating capacity at each moment. For example, a user could perform a deadlift-to-curl-to-overhead press using maximal or near maximal resistances for each part of the exercise. Such an exercise would be appropriate for time-efficient, minimal effective dose workouts [20]. Also, CARE devices are ‘connected’ and record exercise data. Thus, they can be used in telehealth interventions, particularly as the COVID-19 pandemic has caused individuals to shift to home-based resistance exercise, but with less external loading than would be used at gyms [21]. Nevertheless, the impact of resistance training with CARE devices on health and function requires more investigation, including whether SLRT with CARE devices causes different neuromuscular adaptations than SLRT with free weights.
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James L. Nuzzo is Head of Exercise Science Research at Vitruvian, a company that manufactures and sells connected adaptive resistance exercise devices. Kazunori Nosaka has no conflicts of interest with the content of this letter.
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Nuzzo, J.L., Nosaka, K. Comment on: “Stepwise Load Reduction Training: A New Training Concept for Skeletal Muscle and Energy Systems”. Sports Med 52, 2297–2300 (2022). https://doi.org/10.1007/s40279-022-01661-8
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DOI: https://doi.org/10.1007/s40279-022-01661-8