Changes in isometric force‐ and relaxation‐time, electromyographic and muscle fibre characteristics of human skeletal muscle during strength training and detraining

Abstract

Eleven male subjects (20-32 years) accustomed to strength training went through progressive, high-load strength training for 24 weeks with intensities ranging variably between 70 and 120% during each month. This training was also followed by a 12-week detraining period. An increase of 26.8% (P less than 0.001) in maximal isometric strength took place during the training. The increase in strength correlated (P less than 0.05) with significant (P less than 0.05-0.01) increases in the neural activation (IEMG) of the leg extensor muscles during the most intensive training months. During the lower-intensity training, maximum IEMG decreased (P less than 0.05). Enlargements of muscle-fibre areas, especially of fast-twitch type (P less than 0.001), took place during the first 12 weeks of training. No hypertrophic changes were noted during the latter half of training. After initial improvements (P less than 0.05) no changes or even slight worsening were noted in selected force-time parameters during later strength training. During detraining a great (P less than 0.01) decrease in maximal strength was correlated (P less than 0.05) with the decrease (P less than 0.05) in the maximum IEMGs of the leg extensors. This period resulted also in decreases (P less than 0.05) of the mean muscle-fibre areas of both fibre types. It was concluded that improvement in strength may be accounted for by neural factors during the course of very intensive strength training. Selective training-induced hypertrophy also contributed to strength development but muscle hypertrophy may have some limitations during long-lasting strength training, especially in highly trained subjects.

Changes in agonist neural drive, hypertrophy and pre-training strength all contribute to the individual strength gains after resistance training

“…The moderate bivariate correlations between the changes in MVT and agonist EMG in the current study (r = 0.576) were consistent with several previous EMG studies of lower body RT [r = 0.69 (Shima et al 2002); r = 0.74 (Häk-kinen and Komi 1986); r = 0.66 (Häkkinen et al 1985)], but not an elbow flexor RT study (r = 0.187; Erskine et al 2014), which may be significant as the elbow flexors have been found to have a very high level of activation even in the pre-training state (Allen et al 1998;Gandevia et al 1998). In addition, two studies that measured the changes in agonist activation with ITT also found no relationship with individual strength gains after RT (Shima et al 2002;Erskine et al 2010b), although several studies have queried the sensitivity of the ITT to detect changes in activation after RT Harridge et al 1999;Cannon et al 2007;Del Balso and Cafarelli 2007;Tillin et al 2011).…”

“…The relationship between the individual changes in strength following training and the putative underpinning neural and morphological adaptations has previously been investigated primarily using bivariate correlations. These studies have reported changes in strength to be both significantly related and unrelated to the changes in neural [significant: agonist electromyography (EMG): r = 0.66-0.74 (Häkkinen et al 1985;Häkkinen and Komi 1986;Shima et al 2002); non-significant: agonist activation assessed with the interpolated twitch technique (ITT): r = −0.124-0.47 (Erskine et al 2010b), antagonist EMG: r = 0.09 (Erskine et al 2010b) or morphological variables [significant: muscle volume assessed via magnetic resonance imaging (MRI): r = 0.48-0.53 (Erskine et al 2014); non-significant: muscle volume assessed via MRI: r = 0.15 (Erskine et al 2010b); muscle fascicle pennation angle (θ p ) assessed via ultrasonography: r = −0.33-0.26 (Nimphius et al 2012)]. Therefore, there is considerable confusion about the contribution of specific physiological variables to the individual changes in strength.…”

Effects of Supervised Training Compared to Unsupervised Training on Physical Activity, Muscular Endurance, and Cardiovascular Parameters

“…Although not specifically measured, this may be caused from a lack of a behavior change to exercise independently after five months training, which supports previous data [17][18][19]. Prior to beginning this exercise program, all participants were living self-declared sedentary lifestyles.…”

The Importance of Lean Body Mass for the Rate of Force Development in Taekwondo Athletes and Track and Field Throwers

“…The early phase of RFD is thought to be determined mainly by the neural drive to the muscle, as well as the muscle fiber type composition [2,[7][8][9]. Late phase RFD is largely influenced by maximal strength and most likely muscle mass, as suggested by studies reporting parallel changes in maximal muscle strength and contractile RFD 150-250 ms from the onset of contraction [1,2,7,8,[10][11][12][13]. Nevertheless, little is known about the correlation between muscle mass and RFD in power athletes.…”