Cross-education of strength refers to strength gains in the opposite untrained limb. It was previously proposed that the magnitude of cross-education effect may be contingent upon how much stronger the dominant limb is relative to the non-dominant limb before training. Objectives: To examine whether the magnitude of cross-education depends on the baseline strength difference between the dominant and non-dominant arm, as well as individuals’ preference for using their dominant arm in daily activities. Design: Retrospective analyses. Methods: 73 untrained individuals were randomly assigned to either a time-matched non-exercise control group or a training group. The training group performed unilateral elbow flexion exercise with the dominant arm (x3/week for 6 weeks). Maximum strength of the non-dominant was measured before and after the intervention. Moderation analyses were conducted with baseline strength difference and handedness score as moderators. Results: No significant group by baseline strength difference interaction was found for strength changes of the non-dominant arm (i.e., cross-education of strength) [b = 0.255, CI = (-0.259, 0.769), SE 0.257, p = 0.352]. Similarly, there was no statistically significant group by handedness score interaction for strength changes of the non-dominant arm [b = -0.028, CI = (-0.117, 0.062), SE 0.045, p = 0.537]. Conclusions: Six weeks of unilateral high-load resistance training induced a cross-education effect, however, its magnitude was not dependent on baseline strength differences between limbs. The limited variability in handedness in the present sample may have restricted the ability to fully evaluate its potential moderating role, and thus, further research is warranted.

Objectives: To examine whether individualized high-velocity running (HVR) exposure metrics distinguish lower-body soft-tissue injury periods from matched within-athlete control periods in a single professional rugby team, and to evaluate whether such an analysis is feasible with the data one club holds. Design: Retrospective within-athlete matched case-control analysis. Methods: Forty-seven male professional rugby union players were monitored across a 20-week competitive window in 2025 using 10-Hz GPS units; 35 had preseason body-composition records. Fifteen lower-body soft-tissue injuries were identified, and six had monitoring data at both the injury anchor and a within-athlete control anchor 28 days earlier. HVR was defined at 85%, 90%, and 95% of individual maximum velocity. Recency and 7- and 14-day frequency were compared using conditional logistic regression, with Firth-penalized estimation and minimum detectable odds ratios (MDOR). Results: No metric was associated with injury. At 85%, recency odds ratio (OR) was 1.08 (95% confidence interval [CI] 0.88-1.32; 4 pairs), 7-day frequency 1.00 (95% CI 0.14-7.10; 6 pairs), and 14-day frequency 3.00 (95% CI 0.31-28.84; 6 pairs). Four models showed quasi-complete separation and one had no informative strata. MDOR ranged from 1.33 to 25.41. Conclusions: Individualized HVR metrics did not separate injury from control periods. The findings indicate uncertainty rather than absence of effect and illustrate why single-team datasets are poorly suited to individualized HVR injury-risk inference.

Objectives: To compare acute exercise-induced changes in anterior and lateral quadriceps muscle thickness (MT) measured in standing and supine positions. Design: Repeated-measures experimental study. Methods: Fifty healthy adults (18–35 years) performed four sets of unilateral knee extensions to task failure at 70% of one-repetition maximum (1RM). B-mode ultrasound was used to measure anterior and lateral quadriceps MT before and immediately after exercise in standing and supine positions. Measurements were obtained from both the exercised and contralateral control limbs. Results: Anterior thigh MT increased by 0.95 cm in the supine position and 0.68 cm in the standing position following exercise (both p < 0.001), with the increase being greater in the supine position (mean difference = 0.26 cm, p < 0.001). Lateral thigh MT increased by 0.32 cm in the supine position and 0.48 cm in the standing position (both p < 0.001), with the increase being greater in the standing position (mean difference = 0.15 cm, p < 0.001). No significant time effects were observed in the control limb for either site (both p > 0.05). Conclusions: Measurement posture influenced both baseline quadriceps MT and the magnitude of acute exercise-induced changes. Anterior thigh MT increased more in the supine position, whereas lateral thigh MT increased more in the standing position. These findings highlight the importance of standardizing measurement posture when interpreting ultrasound-derived changes in quadriceps MT.