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Sports Weather: The Basis For The VMI 

The "Air Density Index"

Air density is never stable.  It changes with the temperature and primarily with the barometric pressure which fluxuates throughout the day.  Although many professional athletes and pundits have become keenly aware that the thin air of Denver, Colorado allows a golf ball to travel further than at lesser elevations, most of those same individuals would be hard-pressed to identify differentials between Sea Level locations and such venues as Atlanta, Kansas City, Chicago, Dallas, Pittsburgh, etc.  BasketballVMI has provided a unique index from the actual air density found daily in all the venues across the United States.  

The "Neeley Scale" is a gauge of the air resistance available to the athlete and provides the basis for the "Visual Memory Index."  For Basketball, which is played within an arena, the temperature is typically controlled at about 72 degrees Fahrenheit, therefore it would be rare that a temperature difference at game time would occur or be a factor in distance the three-point shot travels given the same thrust from the athlete.  We leave the temperature at 72 degrees and 50% humidity in the ADI formula for each arena at game-time.  The only factor that is considered in the differential between the previous game experience of the athlete and the current Air Density for today's performance is the "Actual Barometric Pressure."

Altitude has an effect on the body of the athlete during performance.

When basketball players transition from a lower elevation to Denver or Utah for an NBA game, it is well documented that they feel "breathless."

The basics of altitude physiology are as follows:  When people, or even animals migrate from a lower altitude to a substantially higher one, it takes approximately 6 weeks for the body to fully acclimate.  The acclimation process is three-fold.  One is the oxygen level in the blood (cardiovascular system).  The second is the oxygen level in the brain (nervous system) and third is the pulmonary system (the lungs).  

As most people in our society are aware, the lungs are the most obviously affected organ and for athletes, the differential during performance can be formidable.  However, the air density also affects the distance a football kick or pass travels so it is not a departure to realize the three-point shot is affected by several inches, as well. 

BasketballVMI's focus is on the distance a three-point shot flies given the athlete's "touch" for the thrust he/she has instinctually developed by performance in a different location than will be in today's or tomorrow's environment.  Some players will adjust during pre-game and half-time warm-ups which may allow them early success.  However, under the tension of game conditions, may revert to their normal shooting later in the game.

The inventor of the basketball Arc shot analyzer once explained to me that the optimum arc of a basketball is 45 degrees going thru the hoop.  See the website at  At that angle, the basketball has only 1-1/2 inches of clearance from the rim both above and below the basketball as it enters the circle.  If an elevation change causes a basketball at the same thrust, to fly further or shorter by more than 1-1/2 inches, it could be a huge performance issue.  

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