Principle #4 - The Right Dose of Cardio

7 Principles to a Better Physique

Q: I know you lift weights, but what do you do for cardio?
A: I lift weights faster
Don't let anyone convince you that "cardio" is a physical state you achieve in the absence of weights - whether it be on a bike, a treadmill, or a skipping rope.

Cardiovascular Demand VS. Oxidative Metabolism / Aerobics
Have you ever finished a challenging set of deadlifts, maybe a 5x5 at 80% 1RM, and realized that even though you took 2-min rest in between sets that your heart is now racing like a jack rabbit?  That's cardio.

Cardio doesn't mean spandex and headbands, and it doesn't mean bobbing up and down on ellipticals for 45min or more.

Cardiovascular training means placing a demand on your heart to increase its rate of contractions (HR in BPM) as well as its stroke volume (SV: amount of blood ejected by left ventricle with each contraction) in order to feed (and flush) working muscles.  Arnold constantly spoke of of "the pump", that feeling of blood-filled muscles creating pressure underneath the skin.  When you lift weights, blood is directed to the working muscles.  As you continue to lift weights (duration), or increase your pace (speed), or increase the weight (intensity/load), this demand for blood increases and SV and HR go up.  Moreover, the heavier the weight, the more mental acuity required.  This increased focus and alertness stimulates and is facilitated by increased HR.

Aerobics is essentially any activity that lasts longer than 90 seconds.  Beyond this point, oxidative phosphorylation/cellular respiration becomes the dominant energy system during continuous exercise.  As exercise duration increases, heart rate and respiration tends to increase.  In most cases, we stay at a pace where we can maintain a constant and steady rate of breathing and heartbeat. 
Engaging in this type of exercise with relative frequency is typically sufficient to improve cardio-respiratory function, mitochondrial density, and oxidative capacity.
However, adapting to exercise and seeing improvements means you have become fitter than you were, which means your aerobic training needs to be more intense to see continued improvement, or to even maintain aerobic fitness (metabolic rate may decrease as much as 5% per decade after puberty). 
By definition, the greatest demand you can place on the heart lies closest to the anaerobic threshold - the point at which the aerobic system cannot produce energy fast enough to address the energy demands placed on it.  If you've ever done interval training with a work-to-rest ratio of 1:1 or less rest, then you know what this intensity feels like.

According to a study by the Journal of Applied Physiology, a low-volume, high-intensity interval protocol of 60s:60s work-to-rest at 90% Max HR over 2-Weeks resulted in improved glucose control and metabolic health:

• reduced avg 24h blood glucose concentration
• reduced 3hr post-meal blood glucose concentration
• increased mitochondrial capacity (~20%)
• increased enzymatic activity (~227%)
• increased GLUT4 content (~369%)
  • transports glucose across muscle cell membrane

TOO MUCH, TOO LITTLE:
You don't want to be doing an hour of aerobic training each day, but then again I wouldn't advise repetitious high-intensity interval training (HIIT) each day either.  The key is balance.  You have two facets to your autonomic nervous system.  The (1) parasympathetic system is responsible for stimulation of "rest-and-digest" or "feed and breed"activities that occur when the body is at rest.  The complimentary (2) sympathetic nervous system's primary process is to stimulate the body's fight-or-flight response. 

When organizing your training it's important to schedule days that facilitate the parasympathetic response, allowing time to "rest and digest" - a Rest Day.  The term rest is relative.  Sometimes you do indeed require a day of absolutely no activity to optimize recovery.  The rest of the time you should aim to, at the very least, alternate training days of higher intensity with days of lower intensity.  It also helps to avoid stimulants (e.g. caffeine) on these days.

Example:
MON - 1hr of weight training paired with 10-15min of HIIT

TUES - 30min of Low-Intensity aerobic exercise 
WED - 1hr of weight training paired with 10-15min of HIIT
THURS - OFF
FRI - 1hr of weight training paired with 10-15min of HIIT
SAT - 30min of Low-Intensity aerobic exercise
SUN - OFF

Sources:
Low-volume high-intensity interval training reduces hyperglycemia and increases muscle mitochondrial capacity in patients with type 2 diabetes. Jonathan P. Little, Jenna B. Gillen, Michael E. Percival, Adeel Safdar, Mark A. Tarnopolsky, Zubin Punthakee, Mary E. Jung, Martin J. Gibala. Journal of Applied Physiology Dec 2011, 111 (6) 1554-1560; DOI: 10.1152/japplphysiol.00921.2011