Losing weight can be a struggle. Success depends on watching what you eat, controlling
for Calories, going to the gym, and doing cardio in addition to the rest of your busy schedule.
The cardio part can be especially confusing. Should you walk for a few hours? Run a few miles?
What about high intensity interval training (HIIT)? There are so many ways to try and tackle
your cardio but for good reason. No matter the cardio type there will be some trade off with your
progress in the gym or what is known as the “interference effect.”
The interference effect is what happens when you lift weights and include cardio as part
of your overall workout routine. Doing more of one will interrupt the progress you make in the
other, which is why there are so many types of cardio. As an example, let’s imagine your goal is
to hit a new one rep max. Running 5 miles post workout becomes counterproductive in your
exercise goal thus the purpose of sprints or HIIT cardio. Exercise researchers have been testing
innovative methods to further limit the interference effect and a new study looks at doing HIIT
resistance training as a potential alternative. Is there yet another new cardio method that can help
gym goers maintain their muscle while losing body fat? Some research suggests that traditional
cardio methods might incur the most benefits for your time though the concept of HIIT training
is very new.
Let’s first look at why cardio and resistance training don’t mix well. The interference
effect is essentially a consequence of the different ways in which your muscle adapts to various
training types. These adaptations are more apparent when comparing endurance to power
training methods. The two types of exercise elicit different physiological changes and those
changes get emphasized the more times you do either workout. When you are improving your
cardio, for example, there are generally three modifications to your cells. Your muscles get better
at utilizing oxygen, they metabolize lactic acid more efficiently, and the number of mitochondria
(energy producers of the cell) increases. 1 These factors can also encourage the muscle to change
fiber type, meaning a larger “power” muscle fiber (Type II) can become a leaner, efficient
“endurance” fiber (Type I) with consistent endurance training. In contrast, strength/power
movements can create a much different cellular environment. Mitochondria are reduced, stress
enzymes are elevated, and overall energy metabolism becomes more efficient. 1. These changes
produce a type II muscle fiber that is more robust and capable of producing bursts of energy over
short durations. To see this difference in the real world, simply compare the musculature and
physique of an elite marathon runner versus an Olympic sprinter. HIIT cardio has been shown to
explain this difference but what does the research say about HIIT training?
A recent publication in the Journal of Strength and Conditioning Research explored this
new approach to further reduce the interference effect. The study compared conditioning and
strength changes when doing HIIT cardio to HIIT training by measuring VO 2 max (conditioning)
and leg strength via leg extension. 2 The participants consisted of strongmen competitors and
strength athletes that were split into a HIIT cardio group and HIIT training group. Those in the
HIIT cardio group performed bike sprints for a predetermined duration in addition to their
regular workout program. The HIIT training group performed a variation of power movements
(squats, deadlifts, etc.) at 60% of maximum load within 2 minutes of the previous set. 2 The hope
was to find a similar conditioning effect with greater strength gains in the HIIT training group.
Instead, the study identified greater predicted strength and VO 2 max in the HIIT cardio group but
no significant between groups in predicted strength. 2 What exactly does this say about HIIT
Cardio or HIIT training regarding the interference effect?
At a glance, the data in this study seems to solidify HIIT cardio over HIIT training but
there is more to glean from this research than one cardio method over another. Yes, HIIT cardio
will probably improve conditioning while reducing the interference effect to a comparable
degree. The jury isn’t out on HIIT training, however. HIIT training hasn’t seen much scrutiny in
the lab up until this point, which means both positive and negative aspects have yet to be seen.
There are a few concerns to consider regarding HIIT training in addition to the lesser outcomes.
Doing HIIT squats, for example, can make for a dangerous situation when going to exhaustion
assuming high intensity is reached. 3 The issue of fatigue can also play a major role. How many
squats can you do in a week before you overreach and your quads can’t recover prior to your
next workout? 3 This study seems to have created more questions than answers regarding cardio.
Until more research can be done, stick to the common recommendations for your aerobic needs.
Keep your cardio sport specific and do the minimum necessary to progress and reduce the
1. Ogan, Jared (2016). Interference Effect: Why Endurance and Strength Training Don’t Mesh. Elite Track Sport
Training & Conditioning. July 29, 2016. <http://elitetrack.com/interference-effect-endurance-strength-training-dont-
2. Androulakis-Korakakis P. Langdown L. et al. (2017). The effects of exercise modality during additional ‘high
intensity interval training upon aerobic fitness and strength in powerlifting and strongman athletes. Journal of
Strength and Condition Research. April 21, 2017. Doi: 10.1519/JSC.0000000000001809.
3. Nuckols, G (2017). Can lifting replace ‘cardio’? Monthly Applications in Strength Sports. Issue 3.