Former executives at Under Armour Inc., the sportswear company whose accounting is under federal investigation, said they scrambled to meet aggressive sales targets, borrowing business from future quarters to mask slowing demand in 2016 for its athletic apparel.

The Baltimore company frequently leaned on retailers to take products early and redirected goods intended for its factory stores to off-price chains to book sales in the final days of a quarter, according to former executives in sales, logistics, merchandising and...