One question would appear on practically every personal trainer survey: Lifting or cardio first during a workout?
The answer is complicated and relies on your fitness level, exercise experience, sporting ambitions, and daily workout time. HIIT and circuit training provide weight training and cardio at the same time, thus it's a false dichotomy.
But if you have general fitness goals, want to separate cardio and strength training in the same program, and want a general rule, here it is: Lift first, then cardio. To maximize your two-a-day workout split, follow these guidelines.
Strength training carries a higher injury risk due to external loading using barbells, dumbbells, kettlebells, resistance bands, etc. Cardio before weightlifting increases danger and affects performance. Simply said, you won't lift as much or do as many reps as you would if you started strength training.
To lift heavy with proper form and maximize development stimulus, your muscles must be fresh. This is impossible if you "pre-fatigue" your muscles with aerobics.
The counterargument is: Will lifting weights before cardio impair aerobic performance? Answer: yes. Research suggests that power, speed, and stamina will decrease, encouraging strength training and cardio on different days.
But lifting weights before aerobic activity won't dramatically raise your chance of injury, which is important to remember when creating your exercises and training plan.