Muskelaktivering av benpress med excentrisk överbelastning

[King Grub]

Purpose:

This study sought to investigate the electromyographic activity of the vastus lateralis (VL) muscle during concentric-eccentric exercise using a new concept leg press machine enabling a preset overloading in the eccentric phase.

Methods:

Ten young males familiar with resistive exercise were recruited for this study. Tests were performed on a Leg-press Biostrength® (Technogym S.p.A., Italy). The load was set to 70% and 80% of one-repetition maximum (1-RM). The participants performed 2 sets of 6 repetitions at each relative load with (ECC +) and without (ISOW) an eccentric overload equivalent to 150% of the concentric load. A metronome was employed to maintain the selected cadence. Sets were separated by a 5-min rest. Surface electromyography (EMG) of VL was recorded and integrated (iEMG).

Results:

Results showed a higher iEMG in ECC + with respect to ISOW at both intensities (+ 29% for 70% 1-RM, p < 0.01 and + 31% for 80% 1-RM, p < 0.001). No statistically significant differences were detected between concentric and eccentric phase in both ECC + conditions.

Conclusions:

Training with a 150% eccentric overload provides a ~ 30% greater motor unit recruitment of the VL muscle in leg press exercise. Moreover, the results show that the eccentric overloading provided by the Biostrength® machine enables training at the same level of neural activation of the concentric phase. Hence, the derecruitment of motor units, normally observed during the eccentric phase when using conventional training machines, was overcome using the Biostrength® machine; this observation seems particularly important for maximizing neuromuscular responses to strength training.

Eur J Appl Physiol. 2020 May 23. Muscle Activation During Leg-Press Exercise With or Without Eccentric Overload.

[Termy]

Fulltext

Det vore intressant framöver om man jämför någon grupp som kör sedvanlig träning och någon grupp med accentuated training / accomodating resistance för att se om t.ex. maxstyrka koncentriskt och andra variabler blir mer effektivt med det ena eller det andra. Kör man tyngre excentriskt i varje koncentrisk repetition så lär man väl antagligen inte orka lika många reps totalt sett? Och hur skulle det stå sig jfr med att köra X antal set med koncentriskt fokus och sedan slänga in ett par excentriskt lagda set på slutet (t.ex. båda armar/ben upp och sedan unilateralt ned)? Många intressanta frågeställningar.

Lite bakgrund i studien till varför man gör på detta sätt:

there is evidence that, for the same absolute load displaced, fewer motor units need to be recruited due to the greater force capacity expressed during lengthening contractions (Duchateau and Enoka 2016). Since the same level of neural activation is required for each value of force and velocity belonging to the same force–velocity curve, it follows that when the same absolute load is displaced within CON and ECC phases of a conventional exercise, motor units must be de-recruited in the ECC phase to enable the load to be lowered (Bigland and Lippold 1953). In this specific case, not only the ECC phase would result underloaded, but it would also fall on another force–velocity curve of a lower activation level (Reeves et al. 2009). Therefore, to avoid this, a greater load should be employed during the ECC phase thereby exploiting the muscle ECC force potential, in line with what predicted by the force–velocity relation of a muscle. Based on such rationale, previous studies focused on the functional adaptations to isolated ECC vs. either conventional (CON + ECC) or CON only training in older (Grimby et al. 1992; Reeves et al. 2009) and young adults (Higbie et al. 1996; Franchi et al. 2014). However, it has been recently suggested that ‘accentuated’ eccentric loading (i.e., the combination of CON and ECC phases with ECC overload) may be a superior type of training for enhancing strength and power performance (Wagle et al. 2017).

TL;DR - mindre rekrytering av motorenheter och därmed muskelfibrer i excentriska fasen av "klassiska" koncentriska set, för att det helt enkelt blir för lätt. Sannolikt då fler typ 1 fibrer istället för typ 2 fibrer som får jobba. = sämre styrkeeffekt i den excentriska fasen.

[Termy]

Om motorenheterna rekryteras fullt ut om man t.ex. kör något excentriskt "dropset" efter slutfört koncentriskt/excentriskt set, fast med samma vikt, verkar ej ha forskats på. Det har man ju i alla fall sett vid hypertrofisk träning då man kör lätt (typ 30 % av 1RM eller högre) då hypertrofin blir likvärdigt om man går till failure då man i slutändan rekryterar samtliga muskelfibrer/motorenheter ändå. Å andra sidan är ju styrkeökningar en annan fråga i sig...