If BLAS threading cannot be controlled and persists with multithreading, consider using explicit parallel processing to ensure proper thread control. For example:

library(parallel)

cl <- makeCluster(1) # Single core

clusterExport(cl, list("explained_variance_aov", "data"))

results <- parLapply(cl, paste0("PC", 1:3000), function(pc) { explained_variance_aov(pc, data, "covar") })

stopCluster(cl)

results <- do.call(rbind, results)