Effects of Acute Loading Induced Fatigability, Acute Serum Hormone Responses and Training Volume to Individual Hypertrophy and Maximal Strength during 10 Weeks of Strength Training

Abstract

This study investigated whether a strength training session-induced acute fatigue is related to individuals' strength training adaptations in maximal force and/or muscle hypertrophy, and whether acute responses in serum testosterone (T) and growth hormone (GH) concentrations during the training sessions would be associated with individual neuromuscular adaptations. 26 males completed the 10-week strength-training intervention, which included fatiguing dynamic leg press acute loading bouts (5 x 10 RM) at weeks two, four, six, and ten. Blood samples were collected before and after the loading and after 24h of recovery for serum T, GH, and cortisol (C) concentrations at weeks 2, 6, and 10. The cross-sectional area of the vastus lateralis was measured by ultrasonography. Isometric force measurements were performed before and immediately after loadings, and loading-induced acute decrease in maximal force was reported as the fatigue percentage. The subjects were split into three groups according to the degree of training-induced muscle hypertrophy after the training period. Increases in isometric force were significant for High Responders (HR, n = 10) (by 24.3 % ± 17.2, p = 0.035) and Medium Responders (MR, n = 7) (by 23.8 % ± 5.5, p = 0.002), whereas the increase of 26.2 % (±16.5) in Low Responders (LR, n = 7) was not significant. The amount of work (cm + s) increased significantly at every measurement point in all the groups. A significant correlation was observed between the fatigue percentage and relative changes in isometric force after the training period for the whole group (R = 0.475, p = 0.022) and separately only in HR (R = 0.643, p = 0.049). Only the HR group showed increased acute serum GH concentrations at every measurement point. There was also a significant acute increase in serum T for HR at weeks 6 and 10. HR showed the strongest correlation between acute loading-induced fatigue and isometric force gains. HR was also more sensitive to acute increases in serum concentrations of T and GH after the loading. Acute fatigue and serum GH concentrations may be indicators of responsiveness to muscle strength gain and, to some extent, muscle hypertrophy.

Keywords: Strength training; acute loading-induced fatigue; individual differences; muscle hypertrophy; serum responses of testosterone and growth hormone; strength gains.

Figure 1.

Overview of the experimental design of the study. CON refers to Control. The control tests lasted one week, the control period lasted one week, and the pre-tests were performed prior the intervention. The training intervention lasted 10 weeks and posts tests were done one week (wk) after the strength training intervention. Acute serum hormone responses were collected at wk 2, 6 and 10. The total length of the intervention was 13 weeks.

Figure 2.

Individual absolute values in VL CSA pre to post (on the left) and individual absolute values in maximal isometric bilateral leg press force pre to post (on the right) after 10 weeks of hypertrophic strength training. PRE=Pre training intervention measurements, POST= post training intervention measurements.

Figure 3.

Maximal isometric bilateral leg press force values during CON and PRE, and repeatedly during the 10-week strength training period for the whole group including individual values. CON=Control measurements, PRE=Pre training measurements. * = compared to Pre. **P ≤ 0.01, ***P ≤ 0.001.

Figure 4.

Fatigue percentages after the acute loading protocol in the leg press at different time points in three different responder groups and in the total group during the 10-week hypertrophic strength training intervention. *P ≤ 0.05, **P ≤ 0.01.

Figure 5.

The correlation between the relative changes in maximal isometric force and fatigue percentage from week 2 to week 10 in the total subject group.

Figure 6.

Relative changes in performed work during the acute loading protocol in the leg press exercise compared to initial week 2 tests in three different responder groups and in the whole group. *P ≤ 0.05, **P ≤ 0.01.

Figure 7.

Acute responses in serum testosterone concentrations during the hypertrophic loading conditions for different subgroups at weeks 2, 6 and 10 during the 10-week strength training intervention. *P ≤ 0.05, **P ≤ 0.01. Pre = before loading, Post = right after loading, Post15 = 15 minutes after the loading.

Figure 8.

Acute responses in serum GH concentrations during the loading conditions for different subgroups at weeks 2, 6 and 10 during the 10-week strength training intervention. *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001. Pre = before loading, Post = right after loading, Post15 = 15 minutes after the loading.