Juha P. Ahtiainen

Muscle hypertrophy, hormonal adaptations and strength development during strength training in strength-trained and untrained men

Hormonal and neuromuscular adaptations to strength training were studied in eight male strength athletes (SA) and eight non-strength athletes (NA). The experimental design comprised a 21-week strength-training period. Basal hormonal concentrations of serum total testosterone (T), free testosterone (FT) and cortisol (C) and maximal isometric strength, right leg 1 repetition maximum (RM) of the leg extensors were measured at weeks 0, 7, 14 and 21. Muscle cross-sectional area (CSA) of the quadriceps femoris was measured by magnetic resonance imaging (MRI) at weeks 0 and 21. In addition, the acute heavy resistance exercises (AHRE) (bilateral leg extension, five sets of ten RM, with a 2-min rest between sets) including blood samples for the determination of serum T, FT, C, and GH concentrations were assessed before and after the 21-week training. Significant increases of 20.9% in maximal force and of 5.6% in muscle CSA in NA during the 21-week strength training period were greater than those of 3.9% and −1.8% in SA, respectively. There were no significant changes in serum basal hormone concentrations during the 21-week experiment. AHRE led to significant acute decreases in isometric force and acute increases in serum hormones both at weeks 0 and 21. Basal T concentrations (mean of 0, 7, 14 and 21 weeks) and changes in isometric force after the 21-week period correlated with each other (r=0.84, P<0.01) in SA. The individual changes in the acute T responses between weeks 0 and 21 and the changes in muscle CSA during the 21-week training correlated with each other (r=0.76, P<0.05) in NA. The correlations between T and the changes in isometric strength and in muscle CSA suggest that both serum basal testosterone concentrations and training-induced changes in acute testosterone responses may be important factors for strength development and muscle hypertrophy.

Short vs. long rest period between the sets in hypertrophic resistance training: influence on muscle strength, size, and hormonal adaptations in trained men.

Acute and long-term hormonal and neuromuscular adaptations to hypertrophic strength training were studied in 13 recreationally strength-trained men. The experimental design comprised a 6-month hypertrophic strength-training period including 2 separate 3-month training periods with the crossover design, a training protocol of short rest (SR, 2 minutes) as compared with long rest (LR, 5 minutes) between the sets. Basal hormonal concentrations of serum total testosterone (T), free testosterone (FT), and cortisol (C), maximal isometric strength of the leg extensors, right leg 1 repetition maximum (1RM), dietary analysis, and muscle cross-sectional area (CSA) of the quadriceps femoris by magnetic resonance imaging (MRI) were measured at months 0, 3, and 6. The 2 hypertrophic training protocols used in training for the leg extensors (leg presses and squats with 10RM sets) were also examined in the laboratory conditions at months 0, 3, and 6. The exercise protocols were similar with regard to the total volume of work (loads 3 sets 3 reps), but differed with regard to the intensity and the length of rest between the sets (higher intensity and longer rest of 5 minutes vs. somewhat lower intensity but shorter rest of 2 minutes). Before and immediately after the protocols, maximal isometric force and electro-myographic (EMG) activity of the leg extensors were measured and blood samples were drawn for determination of serum T, FT, C, and growth hormone (GH) concentrations and blood lactate. Both protocols before the experimental training period (month 0) led to large acute increases (p < 0.05–0.001) in serum T, FT, C < and GH concentrations, as well as to large acute decreases (p < 0.05–0.001) in maximal isometric force and EMG activity. However, no significant differences were observed between the protocols. Significant increases of 7% in maximal isometric force, 16% in the right leg 1RM, and 4% in the muscle CSA of the quadriceps femoris were observed during the 6-month strength-training period. However, both 3-month training periods performed with either the longer or the shorter rest periods between the sets resulted in similar gains in muscle mass and strength. No statistically significant changes were observed in basal hormone concentrations or in the profiles of acute hormonal responses during the entire 6-month experimental training period. The present study indicated that, within typical hypertrophic strength-training protocols used in the present study, the length of the recovery times between the sets (2 vs. 5 minutes) did not have an influence on the magnitude of acute hormonal and neuromuscular responses or long-term training adaptations in muscle strength and mass in previously strength-trained men.

Are skeletal muscle FNDC5 gene expression and irisin release regulated by exercise and related to health

•  Contradictory findings have been reported concerning the function of irisin and its precursor gene, skeletal muscle FNDC5, in energy homeostasis and metabolic health, and the associated regulatory role of exercise and PGC‐1α. •  We analysed the effects of different short‐ and long‐term exercise regimens on muscle FNDC5 and PGC‐1α, and serum irisin, and studied the associations of irisin and FNDC5 with health parameters. •  FNDC5 and serum irisin did not change after acute aerobic, long‐term endurance training or endurance training combined with resistance exercise (RE) training, or associate with metabolic disturbances. A single RE bout increased FNDC5 mRNA in young, but not older men (27 vs. 62 years). Changes in PGC‐1α or serum irisin were not consistently accompanied by changes in FNDC5. •  Our data suggest that the effects of exercise on FNDC5 and irisin are not consistent, and that their role in health is questionable. Moreover, the regulatory mechanisms should be studied further.

Physical exercise increases adult hippocampal neurogenesis in male rats provided it is aerobic and sustained

Aerobic exercise, such as running, enhances adult hippocampal neurogenesis (AHN) in rodents. Little is known about the effects of high‐intensity interval training (HIT) or of purely anaerobic resistance training on AHN. Here, compared with a sedentary lifestyle, we report a very modest effect of HIT and no effect of resistance training on AHN in adult male rats. We found the most AHN in rats that were selectively bred for an innately high response to aerobic exercise that also run voluntarily and increase maximal running capacity. Our results confirm that sustained aerobic exercise is key in improving AHN.

Effect of resistance exercise on muscle steroid receptor protein content in strength-trained men and women

The purpose of this study was to examine the acute effect of resistance exercise (RE) on muscle androgen receptor (AR) and glucocorticoid receptor (GR) protein content. Fifteen resistance-trained men (n=8; 21+/-1 years, 175.3+/-6.7 cm, 90.8+/-11.6 kg) and women (n=7; 24+/-5 years, 164.6+/-6.7 cm, 76.4+/-15.6 kg) completed 6 sets of 10 repetitions of heavy squats. Blood samples were obtained before RE, after 3 and 6 sets of squats, and 5, 15, 30 and 70 min after RE. Muscle biopsies from the vastus lateralis were obtained before RE, and 10 min and 70 min after RE. Blood samples were analyzed for total and free testosterone concentrations and muscle samples were analyzed for AR and GR protein content. Circulating total testosterone increased significantly (p< or =0.05) in men and free testosterone increased in men and women with exercise. AR was significantly reduced at 70 min post-exercise in men and at 10 min post-exercise in women compared to pre-exercise. There were no changes in GR following RE, but GR was significantly higher in women compared to men. These findings support a current paradigm for stabilization followed by a reduction and then a rebound in the acute AR response to RE but demonstrate that gender differences exist in the timeline of the AR response.

Effects of strength and endurance training on antioxidant enzyme gene expression and activity in middle-aged men

This study was aimed at investigating the effects of a 21‐week period of progressive strength or endurance training on peripheral blood mononuclear cells (PBMC) antioxidant enzyme gene expression and activity in healthy middle‐aged untrained men. Strength (n=11) and endurance (n=12) training were performed twice a week, including resistance exercises to activate all the main muscle groups or cycle‐ergometer pedaling, respectively. mRNA levels of catalase, glutathione peroxidase (GPx), mitochondrial superoxide dismutase (MnSOD) and cytosolic superoxide dismutase (CuZnSOD) were increased after 21 weeks of strength training, while endurance training induced significant changes only in MnSOD and GPx mRNA levels. CuZnSOD protein content was significantly increased only in strength‐trained subjects. The program of strength or endurance exercise training had no significant effects on the activity of any of the antioxidant enzymes. In conclusion, in a middle‐aged population, 21 weeks of strength or endurance training was a sufficient stimulus to up‐regulate mRNA levels of PBMC antioxidant enzymes, the strength training being a more optimal stimulus. However, the discrepancies between enzyme protein and mRNA levels suggest that the present systematic strength or endurance training period had no beneficial effects on enzymatic antioxidant defense mechanisms in previously untrained middle‐aged men.

Molecular signaling in muscle is affected by the specificity of resistance exercise protocol

Mammalian target of rapamycin and mitogen‐activated protein kinase (MAPK) signaling pathways have been highlighted as important for muscle adaptations and thus, they may distinguish adaptations to different exercises. Typically, resistance exercise designed for muscle hypertrophy has moderate intensity (60–80% of one repetition maximum, 1 RM) while one prioritizing maximal strength with minor hypertrophy has a higher intensity (≥90% of 1 RM). Eight untrained men (28.4±3.7 years) conducted two different bilateral leg press exercise protocols: hypertrophic (5 × 10 RM) and pure maximal strength (15 × 1 RM) in a counterbalanced, cross‐over design with 1 week between exercises. Vastus lateralis muscle biopsies were taken before and 0.5 h after resistance exercise, or in six controls (26.5±3.6 years) who rested. The phosphorylation of p70S6K (Thr421/Ser424), rpS6 (Ser240/244 and Ser235/236) and MAPK p38 as increased (∼2–16 fold) after both exercise protocols. However, the phosphorylation of MAPK Erk1/2 and p70S6K at Thr389 increased only after 5 × 10 RM. The increase in the phosphorylation of p70S6K (Thr421/Ser424), rpS6 (Ser235/236) and Erk1/2 were higher after 5 × 10 RM (P<0.05). No changes were seen in controls. In conclusion, MAPK signaling is greater after hypertrophic than maximal strength exercise protocol. This may mediate adaptations specific to these different types of training regimens.

Body Composition in 18- to 88-Year-Old Adults—Comparison of Multifrequency Bioimpedance and Dual-Energy X-ray Absorptiometry

This study compared bioimpedance analysis (BIA) in the assessment of body composition with dual‐energy X‐ray absorptiometry (DXA) in 18‐ to 88‐year‐old adults.

Strength Athletes Are Capable to Produce Greater Muscle Activation and Neural Fatigue During High-Intensity Resistance Exercise Than Nonathletes

Ahtiainen, JP and Häkkinen, K. Strength athletes are capable to produce greater muscle activation and neural fatigue during high-intensity resistance exercise than nonathletes. J Strength Cond Res 23(4): 1129-1134, 2009-Acute neuromuscular responses to maximum versus forced repetition (FR) knee extension resistance exercises (4 sets of 12 repetitions [reps] with a 2-minute recovery between the sets) were examined in 4 male strength athletes (SAs) and 4 nonathletes. Maximum repetition (MR) sets were performed to voluntary exhaustion (12 repetition maximum [RM]), whereas in the FR sets, the load was greater (8RM) and the set was continued after voluntary fatigue with 4 additional assisted reps. Maximal isometric force and electromyogram (EMG) activity of the knee extensors were measured before and after the exercise, as well as 2 recovery days after the exercise. Electromyogram activity was also measured during the actual concentric phases of the knee extensions. Both loading protocols in both groups led to decreases in isometric force, but no significant changes were observed in EMG activity during isometric actions at any time points. However, the difference between the 2 loading protocols and experimental groups was observed in muscle activity during the concentric phases of the knee extensions. As expected, EMG activity increased in both groups throughout the MR sets when compared with the first repetitions of the sets. Only in SAs, EMG activity decreased significantly at the end of the FR sets. The results suggest that experienced SAs were capable to activate their muscles to a greater extent than their non-strength-trained counterparts indicated by neural fatigue during the FR exercise. Greater motor unit activation in SAs than in nonathletes may be due to training-induced neural adaptation, which manifested during fatiguing exercise. The present study suggests that FRs are an efficient training protocol to overload the neuromuscular system especially in SAs.

Increased cross-education of muscle strength and reduced corticospinal inhibition following eccentric strength training.

AIM Strength training of one limb results in a substantial increase in the strength of the untrained limb, however, it remains unknown what the corticospinal responses are following either eccentric or concentric strength training and how this relates to the cross-education of strength. The aim of this study was to determine if eccentric or concentric unilateral strength training differentially modulates corticospinal excitability, inhibition and the cross-transfer of strength. METHODS Changes in contralateral (left limb) concentric strength, eccentric strength, motor-evoked potentials, short-interval intracortical inhibition and silent period durations were analyzed in groups of young adults who exercised the right wrist flexors with either eccentric (N=9) or concentric (N=9) contractions for 12 sessions over 4weeks. Control subjects (N=9) did not train. RESULTS Following training, both groups exhibited a significant strength gain in the trained limb (concentric group increased concentric strength by 64% and eccentric group increased eccentric strength by 62%) and the extent of the cross-transfer of strength was 28% and 47% for the concentric and eccentric group, respectively, which was different between groups (P=0.031). Transcranial magnetic stimulation revealed that eccentric training reduced intracortical inhibition (37%), silent period duration (15-27%) and increased corticospinal excitability (51%) compared to concentric training for the untrained limb (P=0.033). There was no change in the control group. CONCLUSION The results show that eccentric training uniquely modulates corticospinal excitability and inhibition of the untrained limb to a greater extent than concentric training. These findings suggest that unilateral eccentric contractions provide a greater stimulus in cross-education paradigms and should be an integral part of the rehabilitative process following unilateral injury to maximize the response.