GORUCK Rucker 4.0 20L - Training BackpackThe GORUCK Rucker 4. 0 20L is a purpose built training backpack designed specifically for rucking, the practice of walking with weighted resistance. Version 4. 0 features enhanced padding at the top of the interior plate pockets for better protection during exercises like burpees and bear crawls, hook and loop closures replacing impact vulnerable zippers, and a more streamlined front panel. The 20L model now includes two elevated plate pockets like