Lactate threshold and summer time running

Endurance exercise is traditionally considered to be a function of three factors.

1. Cardiac output which is , according to the Fick equation, the product of cardiac output and a-v oxygen difference. Cardiac output is  the product of stroke volume and heart rate.
2.Ability to perform at a high percentage of the O2 Max for prolonged periods.This can be measured or approximated by measurement of the lactate threshold.
3.Running efficiency.

 The lactate threshold is lowered during exercise in hot and humid conditions.

Pappadopoulos  et al (1) demonstrated in healthy young men that exercise at a temperature of 98 degrees  the lactate threshold was increased at a lower oxygen uptake ( from 2.86 +/- 0.13 to 2.38 +/- 0.09) while hypohydration was not shown to alter the lactate threshold.


Tanaka and Seals (2) state that there is evidence that the lactate threshold is lowered in older athletes but not when expressed relative to te percentage of 02 max.This suggests that decreases in lactate threshold may be secondary to decreases in 02 max. but however you look at it is lower.

)Pappadopoulos,c et al "Effect of hypohydration on the lactate threshold in a hot and humid environment." J Sports Med Phys Fitness. 2008 48 (3) 293-298

2)Tanaka,H and Seals,DR "Endurance exercise performance in Masters athletes:age associated changes and underlying physiological mechanisms. J Physiol 2008, 586 55-63

Ed Whitlock's marathon record for age 70 has been broken-well sort of

Gene Dykes, age 70, a retired computer programmer , ran a marathon time time of 2:54 23 at the 2018 Jacksonville Florida marathon . This  is faster than the previous accepted "record" of 2: 54 48 set by legendary Ed Whitlock for runners age 70 and over.

But the time may not be   "official" record time  according to the US Track and Field Association who said that the race was certified by them but was not "sanctioned"  which includes a fee paid by the race organizers to the USTFA  as well as a requirement to buy insurance from them .As of  July 10 2019 Wikipedia lists Dykes as holder of the age 70 record.

According to the USTFA a race must be sanctioned by them for any record setting times to be counted .

So far Whitlock still holds undisputed records for the marathon for ages 75,80 and 85 as well as numerous other age records.

Both  Whitlock and Dykes have had their maximal oxygen uptake measured.

Dykes had a 02 max that was surprisingly low for a very accomplished marathoner , 46.9 ml/kilo/min. But he could run at 93% of his 02 max before reaching his lactate threshold.

For comparison, Whitlock's 02 max at age 70 was 52.8 and 54 at age 82.

Pacemakers,ICD -too many too few? need newc guidelines?

About 200,000 pacemakers (PMs) are implanted annually for slow heart rate reasons  ("brady" indications) in the U.S. as are about 100,00 ICD (intracardiac defibrillators).A smaller number of PMs are implanted for CRT (cardiac resynchronization therapy). Data from 2012 quoted about 35,000 for that indication.

A big increase in ICD use occured after randomized trials showed a morality benefit for ICD in heart failure patients .There were two primary prevention trials- previously ICD were for secondary prevention , i.e patients who had survived a SCD event ( sudden cardiac death)

John Mandrola , writing in Medscape ,makes an interesting case for less use of ICD as does a series of excellent comments by his readers. See here.