You need to do cardio. You know you need to do cardio. But you also don't want to risk losing strength. So how do you save your gains? Science has looked into it.
This study included two HIIT workout options for experienced lifters who wanted to increase aerobic fitness without compromising strength.
Sixteen male lifters who'd been training for at least two years and had competed in powerlifting, strongman, or other strength competitions were recruited. They were split into two groups: aerobic and strength. Both groups performed two HIIT sessions a week for eight weeks while continuing their normal training cycles.
Both groups significantly increased their aerobic fitness measures and increased estimated 1RM in the leg extension. In short, neither group lost strength. But there was a difference between the groups for aerobic fitness measures with the aerobic group showing significantly greater changes.
You can increase your aerobic fitness using HIIT-style free weight exercises. The aerobic group showed about double the change in aerobic measures as the strength group though. This shows the aerobic HIIT sessions superiority in producing better aerobic fitness.
Nonetheless, significant aerobic improvements can be made using either aerobic HIIT sessions or strength HIIT sessions while simultaneously increasing strength. So don't be afraid to add a couple of HIIT sessions into your week on top of your normal resistance training volume.
Note: Due to the high volume (56-115 reps of deadlifts or squats) for the strength HIIT workout, don't do this while you're in a preparation period for a meet or competition. The study had the subjects perform these sessions during a general strength/hypertrophy period (off-season).
This underlines the importance of proper resistance programming and proper placement of HIIT sessions in training cycles to obtain maximal strength and aerobic adaptations.