Interesting study, Marinera. I wonder when the IGF-1 was sampled (post-workout, during the workout, or at rest).
Fortunately, the full version of the study is free:
“Blood samples were obtained from an antecubital vein. All subjects reported for blood sampling in the morning after an overnight fast.
For Team 1M, samples were obtained between ~6:00 and 9:00 AM.
For Teams 2F and 2M, fasting samples were obtained between 6:00 and 11:00 AM. Initial samples were obtained at the start of training. Second samples were taken after ~2 mo of training for each team. Third samples were obtained after ~4 mo of training.
This 2- to 4-mo time point represented an interval with the highest training volume completed by all teams. A fourth sample was obtained only from Team 1M, when they were in the middle of their taper on the next to last week of the season. Final samples were obtained ~1 wk after the last competition for Team 1M and after 11-13 days (for 1 subject after 1 wk) after the last competition for Teams 2F and 2M. “
Two previous studies have evaluated the effects of training on resting total IGF-I concentrations (26, 27).
Poehlman et al. (26) observed that cycling training of low-to-moderate intensity for 8 wk partially reverses the age-related decrease in IGF-I concentrations observed in older individuals.
More recently, Roelen et al. (27) found in young subjects that more intense cycling training twice a day for 2 wk produced a 37% increase in resting total levels of IGF-I.
Our results, obtained with young swimmers, showed a positive effect of training on serum levels of total IGF-I. The most striking effects were found for Team 1M, with increases of 70-80% over the last three measurement points.
However, the fact that after 2 mo of training only modest changes in total IGF-I had occurred (women had even lower values) in all groups suggests that a relatively long course of training is required to realize peak adaptive increases in total IGF-I with this type of training. Furthermore, these data show that the elevated total IGF-I concentrations persist even with marked reductions in training volume.
A consistent finding from this work is that resting serum cortisol concentrations became elevated in all groups only at the last measurement, after the taper phase of training and the last competition had been over for 1-2 wk. It is possible that the effects of the high-intensity training and the stress of competition contributed to this phenomenon. Nevertheless, the reason as to why this effect is found at this point of training is unknown.
Full text IGF-1 and training
The study leads to wonder if there is an higher produciton of GH linked to the amount of higher free IGF-1, or maybe a more efficient use of GH, since:
“IGF-1 is a primary mediator of the effects of growth hormone (GH). Growth Hormone is made in the pituitary gland, is released into the blood stream, and then stimulates the liver to produce IGF-1”