Relative strength is the answer to the question "Who is stronger"?
Relative strength is your strength in relation to your body weight. It is a very important concept to understand - not just for sport scientists.
If you think about for which sports this type of strength is important, usually weight category based sports like boxing, judo, weightlifting or wrestling come to mind. However, it is also important for handball players - more than you think! Here is why:
Let's say you weigh 100kg (BW), you squat 100kg (1xBW) and you can jump 40cm high (this is purely finctional). If you increase your squat to 110kg, while staying at 100kg body weight you've increase your relative strength (1,1xBW). Your stronger in relation to your bodyweight. Plus, it is very likely that you've also increased your jump height.
Increasing your relative strength usually results in better performance. Especially when it comes to jumping, sprinting, push ups and pull ups.
HOW TO USE WHEN WANTING TO GAIN MASS
So relative strength is a great way to check if you are actually getting stronger (if that's your goal). If your goal is to increase your body mass it is also a great tool to check if your only gaining fat or also some muscle. So if your goal is mass, and you go from 100kg body weight to 110kg body weight and your squat from 100kg to 110kg as well - your relative strength has stayed the same and your mass has increased (which is good).
HOW TO USE TO KNOW WHO'S STRONGER
By now you should understand that a 100kg squat can be very impressive (if you weigh 50kg) or should be standard (if you weigh 100kg). So next time someone tells you: "Yo, I've benched XYZ" or "I've squatted XYZ" - ask them how much they weigh.
If a wingplayer weighing 80 kg can move a maximum of 105 kg during a bench press, he is stronger from a relative strength perspective than a back player weighing 95 kg who can press 110 kg.
This is because the first person presses 1.31 times their body weight while the second person can only press 1.15 times their body weight.
HOW TO KNOW IF YOU'RE RELATIVE STRENGTH IS GOOD
In the graphic below you can see the strength standards we use in our Strength Training for Handball Programs.
At the top you can see which age group this applies to roughly (or training experience if you didn't start strength training when you were younger). The higher end of the range is for males and the lower end for females. All values or based on your bodyweight.
If you want to improve your relative strength to improve your performance - simply start with the program your current strength values fall within at the moment.