Craig Spencer - This is tough for me to answer, because typically people want an answer that helps them visualize the difference between the two. The difficulty with this, is that players can throw it very different, so it's very difficult for the difference to be explained in visual ball motion terms. The technical difference is "spin time", but what is "spin time"? Well, if I spin a basketball on my finger and a football (on it's side) on my other finger, we know that the basketball will spin a lot longer than the football. The basketball is more symmetric and loses less rotational energy with each revolution. Since the basketball will spin longer, it has a longer "spin time" than the football. Thus, asymmetric cores have a faster spin time and symmetric cores have a longer spin time. The spin time of a core will determine how much time it will need to get through it's entire hooking process. Longer spin time (Sym) will require more time, faster spin time (Asym) will require less time. The key for good ball motion and pin carry is for the ball to get through it's entire hooking process before hitting the pins.
What does that mean for ball motion? Well, asymmetric balls will have a much faster hooking motion and symmetric balls a slower motion. It's better to not look at it so black and white in terms of "Sym" or "Asym", but look at it on a spectrum. When looking up balls online, the terms intermediate differential, Mass Bias, asymmetrical differential or PSA all mean the same thing and tell you how asymmetric the core is. If there is no number, the ball is symmetric, as the number gets higher, the core is more asymmetric. The range will be 0 - .030. Since all balls (including symmetrical) typically become slightly asymmetric after drilling, it's best to view balls on a spectrum and not black and white. The higher that number, the faster the spin time and the faster the ball will transition through it's hooking motion.
What is best depends on your style. Typically, higher ball speeds or lower rev rates with higher axis rotation will have success more often with asymmetric cores because that faster hook phase creates the entry angle they need before the ball runs out of lane and hits the pins. However, as your speed goes down, rev rate goes up with lower amounts of axis rotation you will have success more often with symmetrical balls. These are very general rules though.
How do you eliminate muscle from the swing? - Sean Beck Litchfield Park, Arizona
Josh Blanchard - This is a very good question but also a very easy one to answer. Muscling a swing is usually caused from two things, A) a poor fit, or B) Poor timing and lack of using your legs. The first part you can’t fix yourself, so go see a certified pro shop technician who can fit you correctly or give you suggestions on changes. Once that is fixed and your fit is tight and the ball isn’t going to fall off your hand, you should try and incorporate your legs in your approach more. Especially on your slide step, if you don't already.
Imagine standing at the line with a staggered stance and you swung the ball back and forth without using your legs and threw the ball. To get any speed on the ball, you would have to “muscle” your downswing and use your upper body to throw the ball. This is why muscle in a swing takes over because there is not enough movement in your legs to throw the ball naturally. A good tip would be to try moving your pivot step back on the approach and feel your legs underneath you more as you slide, creating speed and power with your legs; leaving your muscle in the bag.
Craig Spencer - This a great question and is a very common problem in a a lot of sports. In many sports there is almost always something that our arm or arms should be following. In baseball, tennis or golf it's our hips. In those sports, it's easy to add muscle and pull the swing down with our arms instead of letting it follow the rotation of the body. However, in bowling, it's the legs that lead the charge. This is very much a feel thing and is difficult to fix with a simple tip. You are looking for the feeling of letting the ball drop from the top of the back swing. Using your arm only for the direction, and wrist to add rotation. All speed and momentum should come from the legs.
More often than not, most muscle is added to the swing due to fit. If you feel yourself having to grip the ball on the downswing, then you are adding muscle to your swing. Because it takes time, and is a learned skill to grip a bowling ball properly, many bowlers end up using fits that have a bit too much reverse or thumb holes that are too large. Just like in many areas in life, the easier thing comes at a sacrifice. Always check with your pro shop guy first, but grab an old ball at home, plug and re-drill it to try a fit that reduces grip pressure. Add a 1/4" forward to your current pitches, but make sure that your pro shop adjusts your span accordingly for the pitch change. If you start off with slower throws and work your way up, you will eventually clear the new fit just fine, and when you go back to your old one, you will notice how much more you had to squeeze to hold on to it. Other then fit, all I can recommend is to try and focus more on rolling the ball into the lane instead of throwing the ball at your target.