Carl

Although there is no such thing as a perfect estimate, there is a better formula for calculating max hr in runners. It's in 'Heart Rate Monitor training for the Compleat Idiot'. You can get it from Amazon, but note the spelling of COMPLEAT.

Anyway, using that calculation (205 minus half your age), your max hr is 188

Now subtract your resting hr

188-48=140

now we multiply 140 by the %

so 140 x .6 =84

140 x .65=91

140 x .7 =98

140 x .75=105

140 x .8 =112

140 x .85=119

140 x .9 =126

140 x .95=133

finally, to get your zones, add your resting hr on again.

Your zones are as follows

60-65% 132-139 bpm

65-70% 139-146

70-75% 146-153

75-80% 153-160

80-85% 160-167

85-90% 167-174

90-95% 174-181

Just to throw a spanner in the works, some people have an actual max hr which is up to 20bpm different from the formula calculations, so it is advisable to do a max hr test- mind you, I haven't got round to doing one yet!