To assess the magnitude of change and association with variation in training load of two performance markers and wellbeing, over three pre-season training blocks, in elite rugby union athletes. Observational. Twenty-two professional players (age 25±5 years; training age 6±5 years; body mass, 99±13kg; stature 186±6cm) participated in this study, with changes in lower (CMJ height) and upper body (bench press mean speed) neuromuscular function and self-reported wellbeing (WB) assessed during an 11-week period. There was a small increase in CMJ height (0.27, ±0.17 - likely substantial; standardised effect size, ±95% confidence limits - magnitude-based inference) (p=0.003), bench press speed (0.26, ±0.15 - likely substantial) (p=0.001) and WB (0.26, ±0.12 - possibly substantial) (p<0.0001) across the pre-season period. There was a substantial interaction in the effect of training load on these three variables across the three training phases. A two-standard deviation (2SD) change in training load was associated with: a small decrease in CMJ height during the power phase (-0.32, ±0.19 - likely substantial) (p=0.001); a small reduction in bench press speed during the hypertrophy phase (-0.40, ±0.32 - likely substantial) (p=0.02); and a small reduction in WB during the strength phase (-0.40, ±0.24 - very likely substantial) (p<0.0001). The effects of changes in training load across other phases were either likely trivial, only possibly substantial, or unclear. The effect of training load on performance can vary both according to the type of training stimulus being administered and based on whether upper- or lower-body outcomes are being measured. Copyright © 2019 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.