Failure is a state where it is impossible for you to complete a repetition under good form - despite your best effort.
When we provide a number of reps to complete along with the cue to 'go to failure' - you are aiming to reach failure at that number. This will determine the weight you need for the set.
Sometimes we may specify a 'Rep Range' that we want you to achieve failure within.
For example, if we specify a rep range of 8-10, achieving 8, 9 or 10 reps before hitting failure would be successful. The aim is to get more reps than the range dictates so that you can increase the weight, and in turn, fall within the rep range (and once again try to increase the reps to repeat the cycle).
- If you get less reps than the range dictates, the weight was too heavy.
- If you perform more reps than the range dictates, the weight was too light.
In this case you want to use this data to determine what weight to use next time you repeat the workout. You may need to increase or decrease the weight, or perhaps if you keep the weight the same, you may be able to reasonably progress the reps so that it falls within the range.
The more that you train, the easier it is to understand your body and get used to your potential.