Muscle fatigue during maximal eccentric‐only, concentric‐only, and eccentric‐concentric bicep curl exercise with automated drop setting

Abstract

Connected adaptive resistance exercise (CARE) machines are new technology purported to adjust resistance exercise loads in response to muscle fatigue. The present study examined muscle fatigue (strength loss, fatigue perceptions) during maximal eccentric‐only (ECCmax‐only), concentric‐only (CONmax‐only), and coupled ECC‐CON (ECCmax‐CONmax) bicep curl exercise on a CARE machine. Eleven men and nine women completed the three protocols in separate sessions and in random order. All protocols included 4 sets of 20 maximal effort muscle contractions. Strength loss was calculated as Set 4 set end load minus Set 1 highest load. The CARE machine's algorithm adjusted resistances automatically, permitting continued maximal effort repetitions without stopping. Consequently, all protocols caused substantial fatigue. Women were most susceptible to strength loss from exercise that included maximal efforts in the ECC phase, whereas men were most susceptible to strength loss from exercise that included maximal efforts in the CON phase. With ECCmax‐only exercise, ECC strength loss (mean ± SD) was similar between men (55.9 ± 14.1%) and women (56.4 ± 10.8%). However, with CONmax‐only exercise, men and women experienced 55.6 ± 6.2% and 35.3 ± 8.7% CON strength loss, respectively. With ECCmax‐CONmax exercise, men experienced greater ECC (62.9 ± 7.7%) and CON (77.0 ± 5.3%) strength loss than women (ECC: 48.5 ± 15.7%, CON: 66.2 ± 12.1%). Heightened perceptions of fatigue and pain of the exercised limb were reported after all protocols. Women generally reported more biceps pain than men. The results illustrate CARE technology delivers ECC‐only and accentuated ECC exercise feasibly. Acute responses to repeated maximal effort bicep curl exercise with such technology might differ between men and women depending on muscle contraction type.

Overview of muscle fatigue differences between maximal eccentric and concentric resistance exercise

“…15 We identified relevant studies using a mixed approach similar to that described by Greenhalgh and Peacock. 17 This approach relied on the investigators' personal knowledge and checking of personal digital files associated with previous research, 5,6,18,19 keyword searches performed in PubMed and Google Scholar (e.g., "eccentric" AND "concentric" AND "fatigue"), and "snowballing" strategies (i.e., reference and citation tracking). Articles were eligible for inclusion in the review if they included human subjects and reported muscle strength data (e.g., torques, forces) before and at the end of acute bouts of ECC max , CON max , or coupled ECC max -CON max resistance exercise.…”

“…In one study, participants exercised with maximal effort on a connected adaptive resistance exercise machine, which involved maximal muscle actions performed within a range of velocities and with an external resistance that decreased (i.e., drop setting) in real-time to match the participant's force-generating capacity with fatigue. 5 The ECC max and CON max exercise protocols typically involved a prescribed number of sets and repetitions. The protocols ranged from 1 to 10 sets (3.4 ± 2.5 sets) and from 6 to 100 muscle actions per set (29.3 ± 28.5 repetitions).…”

“…Historically, the ability to complete sets of repeated ECC or CON exercise was limited to isokinetic dynamometers, which, although regularly used by researchers, 1 have not been widely adopted by strength and conditioning coaches, 2,3 and are rarely found in fitness centers. New exercise technologies [4][5][6][7] have potential to make completion of submaximal and maximal ECC or CON resistance exercise more feasible outside of the laboratory. Thus, increased participation in these modes of resistance exercise, particularly ECC, is anticipated in the future, and the acute physiological responses to such exercise should be understood to guide exercise prescriptions.…”

Connective Adaptive Resistance Exercise (CARE) Machines for Accentuated Eccentric and Eccentric-Only Exercise: Introduction to an Emerging Concept

“…This drop setting feature, first described elsewhere [33], enabled the individual to perform the greatest possible number of repetitions on the machine without need to disengage from it, and this occurred for both the accentuated eccentric and eccentric-only exercise. Two recent experiments [59,60] have confirmed the automated eccentric overload and drop set features of the machine and also validated the machine's load in different ways: (a) strong correlations (r ≥ 0.94) were found between maximal concentric phase strength on the machine and a one repetition maximum test with a dumbbell; (b) agonist muscle activity during maximal effort repetitions on the machine was equal to or greater than during a one repetition maximum test with a dumbbell; and (c) during fatiguing exercise on the machine, heightened perceptions of fatigue occurred in concert with strength loss. Data in Fig.…”

“…Here, our purpose is to illustrate the potential of CARE technology to deliver accentuated eccentric and eccentriconly resistance exercise rather than to discuss the particular advantages and disadvantages of each machine. To illustrate the potential of CARE technology for delivering eccentric resistance exercise, we describe one CARE machine (Trainer + , Vitruvian, West Perth, Australia) We describe this machine because it is the one we are most familiar with [33,59,60] and because it exhibits most features of eccentric exercise technologies recommended by Tinwala and colleagues [19]. For example, the machine has distinct modes for accentuated eccentric and eccentriconly exercise, permits multiple degrees of freedom, has an easy-to-use interface via its mobile phone application, and provides real-time performance feedback and options for downloading and sharing results.…”