Difference between revisions of "Predicting maximal strength"

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'''How to use this graphical calculator?'''
 
'''How to use this graphical calculator?'''
Suppose you managed to do 9 repetitions with a weight of 80 kilograms.  In the graphical calculator below drag the black dot to r=9 and the blue dot to weight=80. Then the 1RM prediction of 95.43 is displayed.
+
Suppose you managed to do 9 repetitions with a weight of 80 kilograms.  In the graphical calculator below you have to drag the black dot to r=9 and the blue dot to weight=80. Now, you can read of the 1RM prediction of 95.43.
  
 
<jsxgraph width=700 height=500>
 
<jsxgraph width=700 height=500>

Revision as of 10:04, 18 August 2009

This little application tries to predict the maximal strength (1RM) based on a repetitions to fatigue (RTF) value.

The calculation is based on the so called KLW formula:

[math] 1RM = w\cdot(0.988+0.0104\cdot x+0.00190\cdot x^2-0.0000584\cdot x^3) [/math]

The horizontal axis denotes the number of repetitions, the vertical axis denotes the ratio 1RM/RTF.

How to use this graphical calculator? Suppose you managed to do 9 repetitions with a weight of 80 kilograms. In the graphical calculator below you have to drag the black dot to r=9 and the blue dot to weight=80. Now, you can read of the 1RM prediction of 95.43.

References

  • W. Kemmler, D. Lauber, J. Mayhew, and A. Wassermann: "Predicting Maximal Strength in Trained Postmenopausal Woman", Journal of Strength and Conditioning Research 20(4), (2006), pp. 838-842.

The underlying JavaScript code

<jsxgraph width=700 height=500>
var brd = JXG.JSXGraph.initBoard('jxgbox',{boundingbox:[-1,1.8,30,0.8]});
bx = brd.createElement('axis', [[0,0.9], [1,0.9]], {});
by = brd.createElement('axis', [[0,0], [0,1]], {});

var w = brd.createElement('slider',[[24,0.92],[24,1.7],[0,50,200]],{name:'weight w',snapWidth:1});

f = function(x){ return (0.988+0.0104*x+0.00190*x*x-0.0000584*x*x*x); };

var c = brd.createElement('functiongraph',[
             f,
             1,22
             ], {strokeColor:'black', highlightStrokeColor:'black'}
             );

var r = brd.createElement('glider',[10,1,c],{name:'',fillColor:'black',strokeColor:'black',style:6});
var t = brd.createElement('text',[function(){return r.X()+1;}, 
                                  function(){return r.Y();}, 
                                  function(){return "repetitions r = " + Math.floor(r.X());}]);

brd.createElement('text',[5,1.6, 
                          function(){return "predicted 1RM = " + (w.Value()*f(Math.floor(r.X()))).toFixed(2);}],
                         {fontSize:'24px',strokeColor:'red'});

</jsxgraph>