The effect of selected genetic variants, age, sex and training methods on physical activity, capability and trainability

Abstract

The main objectives of this thesis were to investigate the role of selected genetic variants on physical activity (PA), capacity and trainability in homogenous cohorts from South-Eastern Norway. Two of the cohorts (Papers I and II) represented the general population, and the third consisted of well-trained cross-country skiers (Paper III). We wanted also to investigate how age and sex influence the response to maximal strength training (MST) and performance adaptations in cross-country skiing.

In Paper I, three polymorphisms were investigated (ACTN3 R577X, ACE I/D and uVNTR MAOA). Questionnaires were used to divide individuals (n=831) with the mean age (± SD) 55.5 ± 3.8 years (yrs) into groups with either low/medium (LMPA) or high PA (HPA) levels. We investigated the associations between the PA levels and the polymorphisms as well as with several socio-economic variables. We found 10% fewer ACTN3 R577X X allele carriers in the HPA group compared to the LMPA group (p<0.01). Education and previous participation in sports or outdoor activities were positively associated with the PA level, and females reported higher PA levels than males (p<0.01)

In Paper II, we genotyped three polymorphisms (ACTN3 R577X, ACE I/D and PPARGC1A rs8192678). 49 subjects (males and females aged 20-76 yrs) completed a MST intervention in leg-press. For 8 weeks subjects trained three sessions/week with each session consisting of 4 · 4 repetitions at ~85-90% of one-repetition maximum (1RM) intensity. At pre- and post-tests, 1RM was tested. We found an average 24% increase in 1RM (p<0.01) independent of age, sex and, surprisingly, training status. Carriers of the PPARGC1A rs8192678 T allele were 15% stronger at baseline (sex- and age-corrected 1RM) compared to individuals with CC genotype (p<0.05). The C allele carriers exhibited 34.2% larger improvements in 1RM (%) than homozygotes for the T allele (p<0.05). A trend was observed towards improved response to MST among the individuals with the ACTN3 R577X RR genotype compared to the XX (30% vs. 19%).

In Paper III, seven polymorphisms were investigated (ACTN3 R577X, ACE I/D, ACSL1 rs6552828, IL6 rs1474347, PPARA rs4253778, PPARG rs1801282 and PPARGC1A rs8192678). The study was a 6-month observational study (May to October) based on a cohort of well-trained cross-country skiers (n=29; 16-48 yrs). A number of physiological tests were performed prior (Pre-test), half-way (Post1) and after (Post 2) the study period. Throughout the study, participants maintained and reported their training habits. We found several associations between several of the genetic variants and various physiological/performance variables. For instance, ACTN3 R577X X allele carriers exhibited better DP-VO2max (55.4 vs. 59.4 mL-1·kg·min-1; p<0.05) compared to the RR genotype. Individuals with the XX genotype had, however, poorer work economy than the R allele carriers (0.820 vs. 0.765 mL-1·kg-0.67·m; p<0.05). In regard to other variables, we found a significant effect of age and sex on TTDP (p < 0.01), DP-VO2peak (p < 0.01), CDP (p < 0.05), MAS (p < 0.01), LTv (p < 0.01), 1RM half squat (p < 0.01) and 1RM pull-down (p < 0.01). Sex had also an impact on RUN-VO2max (p < 0.01). The total training volume consisted of ~90% low-intensity training and 5% moderate and high-intensity training, each (range: 357.5 - 1056.8 min/week). During the study, there was a significant increase in the total volume and ski-specific training (p < 0.05), but the intensity distribution remained the same. We did not observe any improvements in either physiological/performance variables for the whole cohort or training progression/adaptation between age groups or sexes during the 6-month period.

All in all, our results point towards a potential role of the investigated polymorphisms on the complex traits investigated, i.e. PA levels, maximal strength and endurance performance. Also, for all the genes, the allele frequencies were similar to those reported previously in other European populations. Another important observation was that, although age and sex had an effect on both strength and endurance performance, these factors appeared not to affect the adaptability to maximal strength training or endurance training. Training modality was shown to be highly important, as all participants of the leg-press study (Paper II) improved their maximal strength in response to the MST. In the cross-country study (Paper III), however, no significant changes in endurance parameters were observed during the 6-month study period. Although the participants increased their total training volume, they maintained the same training intensity.