Not surprisingly, aerobic training
is more effective than resistance training for weight loss. However, caveats
abound. Please read on…
From the literature review, it
becomes clear to me two things. Exercise scientists should foster
collaborations, agree on a common methodology to measure something, and combine
efforts for recruitment to increase participant number. This would make the literature
much less muddled and difficult to navigate.
Before I go deeper, however, I
wanted to state my opinions.
First, I think exercise should not
be for weight loss. I believe that exercise should be an integral part of
everyone’s life. Our bodies were evolutionarily designed to walk for days (see controversial
books written on this subject such as “Born to run”, great read by the way), we were not meant to sit
around all day. Yes life requires us to sit around for hours before the
computer, but that doesn’t mean you can’t spare one hour out of your day
exercising (that’s 1/16 of your time awake, be honest and say you don’t spend
more time on social media). It’s for your own health and longevity, sanity and
happiness (yes it has been shown in gazillions of studies that exercise leads
to these things, we shouldn’t need to argue this).
Second, you should eat healthier. I
know I should, and I already eat better than you. Our bodies are not designed
to ingest so much rich, processed, garbage. Eat nutritious food and begin to
enjoy it. You will feel better about yourself and who you are.
Third, stop making excuses for
yourself. If you truly want to be healthy do it today. Make plans and
discipline yourself. I know plenty of extremely busy people who somehow work in
time to exercise. My MSc mentor runs to work pushing his baby in front of him.
My PhD mentor has a treadmill-desk in his office that he walks on all day, and
he’s one of the most prolific scientists I’ve ever met. You know that
everything that you treasure in your life, you’ve had to work your ass off for.
Reward takes dedication and hard work. Don’t think that health is something
else. Health requires discipline and hard work.
Now I feel better. Now let’s talk
about how exercise science is done.
Aerobic vs.
resistance training
Aerobic training (AT) is generally
defined in the field as moderate intensity exercise (50-70% VO2max)
for at least 30 minutes, usually done on a treadmill, exercise bike, or
ergometer (Howley et al. 1994). VO2max,
or maximum oxygen consumption/uptake, defines the aerobic physical fitness of a
person (Howley et al. 1994; Ronnestad
and Mujika2014). This test, if properly conducted, needs to involve a graded
exercise test on a treadmill or cycle ergometer. Exercise intensity is
gradually increased, while oxygen and carbon dioxide intake and output values
are measured (yes you have heard of this test). However, this method is tedious
and requires an expensive set-up. Therefore, estimates of VO2max can
also be made, but these are not accurate measurements. Most studies I reviewed
used an estimation for simplicity, a potential source of error.
Resistance/strength training (RT) involves
repeated muscular contraction generated against an external resistance
(weights/bodyweight). The stimulus of resistance against muscle contractions
cause perturbations in skeletal muscle tissue that directly leads to muscular
growth (i.e., hypertrophy; Schoenfeld
2010), and increases in strength, endurance, and coordination (Stone et al. 1991). Measures of improvement
post-RT thus usually involve tests of strength, endurance, and lean mass.
Strength and endurance improvements can of course be accurately quantified.
However, body composition (body fat%/lean mass) measurements can be inaccurate
when using techniques such as skinfold measurement (using calipers to
measurement thickness of skin folds in certain areas then plugging the
measurement into a general equation, Jackson and Pollock 1978), depending on the
technician, and can introduce error into studies. Underwater weighing, applying
Archimedes’ principle of the different relative densities of fat and muscle in
water, is thought to be the most accurate measurement of body composition
(Wilmore 1969). However, this method is tedious, and have been replaced largely
by new, relatively accurate, technologies such as the BOD POD, which is a
chamber that one sits in while the volume of air and the weight of a person is
measured (like underwater weighing).
Lack of large
randomized trials with conclusive evidence
A large
body of evidence supports AT and RT as important regimes to follow for general
health maintenance (ex. Cardiovascular
health, insulin sensitivity and glucose tolerance, VO2max, body composition,
bone density etc., Donnelly et al. 2009). The purpose of my blog is
not to list these studies and their results, but to critically analyze the body
of evidence that supposedly supports these conclusions.
Most of studies I found addressing
effects of AT/RT on weight loss look at either exercise regimes alone, most
likely due to a lack of participants (usually 20-30 total participants in each
study). With such a small number of participants, sampling error starts to
become a problem.
Furthermore, the population chosen
is not random (a major statistical no-no). Majority of studies had
overweight/obese participants that were sedentary before the study. Conclusions
drawn from this subset of people cannot be extrapolated to the general
population. Just because overweight/obese people have high chances of heart
disease doesn’t mean an average person does as well, same goes for weight loss
resulting from a certain amount or type of exercise. Additionally, if you
already carry around a large amount of excess weight (hence “overweight”), your
body is more likely to lose this weight.
As with cooking roast beef, studies
of the effects of AT and RT cannot agree about methodology. For RT, some
studies incorporated 2 days of exercise per week (Chilibeck et al. 1997), some 5 days per week
(Yarasheski et al. 1993). Total time
for studies ranged from 2 to 20 weeks. Some studies called for strict diet or
calorie maintenance, while others did not. The exercises done were very
different, although most were done using machines, which is I think the least
effective way to do resistance training for general populations. One does not
simply compare results of studies that incorporate such different programs.
Needless to say, results vary tremendously from study to study. Some report
weight loss but some don’t. However, most report a significant increase in lean
mass and strength (Chilibeck et al. 1987;
Starom et al. 1989; Starom et al. 1994; Prabhakaran et al. 1999; Yarashaski et al. 1993).
On the AT side, study methods were
just as inconsistent. Studies were done on ergs (Geliebter et al. 1997; Miller et al. 2002;
Posner et al. 1992; van
Aggel-Leijssen et al., 2001),
treadmill (Raz et al. 1994; Lambers et al. 2008), at between 40-70% VO2max,
with a weekly exercise time between 120-225 minutes (4X30minute sessions to
4X1hour sessions). Some studies lasted a year (Anderson et al. 1995; Irwin et al. 2003),
while others lasted 8 weeks (Geliebter et
al. 1997). Study participants were very different, but mostly involved sedentary
overweight individuals.
Results were abysmal for randomized
trials of AT on weight loss. Average weight loss for participants were not
higher than 3kg (Abe et al. 1997),
with most hovering around 1kg even though the program lasted 1 whole year (Anderssen
et al. 1995)!!! Why did they only
lose 1 kg? Because the programming sucked. Anderssen et al. 1995 called for 3X/week of exercise at 50-60% max heart rate
for one hour. This kind of workout plan was routine in all the studies. How can
these people lose weight if they are not working hard enough? Intensity =
results. Importantly, Anderssen et al. 1995
also incorporated a group that went on a diet restriction plan and exercised.
This group lost an astonishing 6kg!!!! I will discuss the importance of diet on
weight loss below.
The most systematic study
addressing the effects of AT vs. RT on weight loss is a study led by Dr.
William Kraus from Duke University Medical Center (Steutz et al. 2011; Willis et al. 2011).
The study, published in two papers (I hate when people split data into
different papers by the way), was a large randomized trial of 196
overweight/obese sedentary men and women doing either AT, RT, or both AT and RT
for 8 months. The effect of these three exercise regimes on metabolic
parameters (Steutz et al. 2011) and
general weight loss parameters (Willis et
al. 2011) were tracked and analyzed. All groups lost a significant amount
of weight (2kg for AT only, AT and RT, 0.7kg for RT only). Interestingly, the
AT alone group had the best results in fat loss, VO2max and metabolic
parameters such as liver density. The RT, as expected, had the largest
improvements in strength and lean mass.
Surprisingly, people doing both AT
and RT (and therefore exercising for twice as long) did not show better weight
loss, improvements in metabolic parameters, or strength increase than either
the AT or RT alone. This does not mean that people doing AT and RT did not
improve their strength and lean mass more than the AT alone group. However, it
did not seem, at least in these middle-aged overweight men and women, that
doing twice as much exercise meant twice the results. The results were still amazing
though: AT and RT men and women on average dropped body fat percentage by 2%!
Particularly considering that none of these people were put on a strict diet
plan!
Some weird/interesting things in
this study:
Even though both studies looked at
the same group of people, the number of participants reported in each paper was
different. Whether this was due to data missing from certain people, or because
the data from these people did not bode well for the researchers’ conclusions
is unknown.
Most importantly, the AT and RT
group did both exercise regimes back to back. People get tired, especially
sedentary people. Tired people don’t exercise well, and the amount of effort
you put into something is definitely correlated with results (I’m not citing
anything here because this statement is both philosophical and factual, if you
have a problem with it you must be crazy). Therefore, I believe that AT+RT did
not lead to additive effects on the parameters tested because the people were
too tired to give their 110% in their second consecutive workout. I would have
asked the people to commit more days to the study so that they can do aerobic
training one day and resistance the next. I believe that this would have led to
much better results for the AT+RT group.
Basically I find it hard believing
that if one works out twice as hard one does not get twice the results. Call me
a romantic. Also, if the participants were on put on a well-planned diet, their
results would have been incredible!
In addition to exercise,
diet is key
The importance of a diet
supplementing an exercise plan is demonstrated (I think conclusively) by a
meta-analysis study by Miller et al. 1997.
A meta-analysis tries to combine data from different studies and measure the
overall effect of a given treatment, here diet vs exercise, or both combined.
Although many pitfalls arise, more trustworthy patterns emerge as factors that
might bias studies are averaged, and data points (subjects) increase.
Over the 700 studies looked at by
Miller et al. (1997), only 33 people on
average participated in each study (this includes all the different groups).
Most studies were not randomized, meaning the experimenters could introduce
bias by accident. Frighteningly, most studies did not even include a control
group!! Miller et al. (1997) also
found that the type of people that participated in these studies were
different. Exercise studies involved people who were younger and less obese, or
not at all. One can imagine that a person with more unneeded body weight can
lose weight and fat easier.
Regardless, the main findings of
Miller et al. (1997) were incredible,
if not slightly surprising to me: while exercise alone led to significant
weight loss (3 kilograms), diet led to more than 10 kilograms of weight loss!!
Surprisingly, people who did both diet and exercise did not have more
significant weight loss than people who just went on a diet. However, these
people were better able to maintain the weight lost after one year. It appears
that while the common knowledge that diet and exercise are both important for
weight loss, the well-known saying that it’s 80% nutrition and 20% exercise may
hold true for the purpose of weight loss in overweight/obese individuals.
From my
review of the literature, it appears that most generally well-known fitness
advice has strong scientific support. Despite the shortcomings in most exercise
science studies, the overwhelming evidence supports the fitness myth: aerobic
exercise is better for weight loss than resistance training. So, stop eating the roast beef and make some chicken breast and salad instead.
Also, I know you don’t want to
just lose weight. You want to be healthy. To be healthy and strong, you should
improve your strength and do some resistance training. Go get it ;)
In my next blog post, I will
critically discuss studies addressing the question: what is the most effective
diet for losing weight and keeping off the pounds?
References:
