Sprints – 30s Versus 60s


Today I will be summarizing a recent study that evaluated sprint interval training on rate of perceived exertion on 20 healthy participants, entitled “Exertional Responsese to Sprint Interval Training: A Comparison of 30-sec. and 60-sec. Conditions”

I’m a huge fan of sprints (versus steady state cardio) – you can read more about my experiences with long distance running on my about page. I usually switch up the length of my sprint intervals (anywhere between 30 to 90s), so this article was interesting to me.

Usain Bolt – the sprint master


20 students (average age 23.4) were recruited from a university in the US. They were all screened for prior/existing health conditions (orthopaedic, cardiovascular or pulmonary). They were instructed to avoid alcohol, caffeine, and tobacco for three hours prior to testing.

Two groups were established, both consisted on 20 minutes (2 min warm up, 16 min intervals, 2 min cool down) on a stationary cycle, one with 60s intervals, one with 30s intervals, with a 1:1 rest period (i.e.60s on, 60s off vs. 30s on, 30s off)

The investigators tested each participant for peak workload capacity by determining the point at which they couldn’t maintain a cadence of 30rpm. They were then given 3-5 minutes of active recovery.

After recovery, each participant began the interval trial. The intensity used for sprint intervals was 90% peak power achieved on the first test.

The outcome of interest was a valid and reliable rate of perceived exertion (RPE) scale,i.e. how hard did the participant think they were working, on a scale of 0-10. This is a standard scale that trainers use to assess how hard they think their clients are working.  (0 is nothing at all, 3 is moderate, 5 is hard, and 10 is very, very hard or maximal.


Both trials showed a significant increase in RPE from before the trial to after the trial. RPE for the 60s trial was significantly higher both after, and during exercise.


Shorter intervals are perceived as less work than longer intervals, even though the participants were sprinting and resting for the exact same time!

Unfortunately the only variable the authors evaluated was the RPE, I would be interested to see the effect of interval duration on VO2 max, heart rate, calorie expenditure etc. There might be a trial out there that already evaluated this though, I’ll have to check!


Kilpatrick, M.W., Greely, S.J. Exertional responses to sprint interval training: A comparison of 30-sec. and 60-sec. conditions. 2014 Psychological Reports. 144 (3) 854-865.


High Protein vs. High Fat Snacks

I’ve already summarized a study comparing low-carb to low-fat diets, now let’s look at snacks!

  VS  VS. 

This study compared appetite control and satiety following high-protein vs. high fat snacks in healthy women.


Twenty pre-menopausal women were included (average age 27, BMI 23.4). Authors excluded smokers, participants with food allergies, eating disorders, diabetes, recent rapid weight loss/gain or were on any medication that would alter appetite.

Participants were randomized in a crossover design to consume one of three afternoon snacks for three consecutive days.

1. greek-style yogurt (14g protein, 25g carbs, 0g fat)

2. crackers (0g protein, 19g carbs, 9g fat)

3. chocolate (2g protein, 19g carbs, 9g fat)

On the fourth day, participants consumed a standardized breakfast meal (18%P, 61%C, 22%F), and reported to the center for testing.

During testing, they consumed a standardized lunch, followed by their respective snack (3h later).

Then, they were asked to complete scales on how much they liked the snack, and on appetite sensations every 30 minutes until they requested dinner


Post snack hunger was significantly lower at 90 minutes compared to the chocolate and cracker snacks.

Post snack fullness at 90 minutes was significantly greater than the chocolate snack, but not the crackers.

Consumption of yogurt snack delayed dinner eating by ~30 minutes compared to the chocolate snack, and ~20 minutes compare to the crackers. 

Dinner intake was approximately 100kcals fewer when participants consumed the yogurt snack compared to the others. 

Limitations of this study include the fact that they did not standardize or record what the participants ate during the initial 3 days along with the short time period and small sample size. Additionally, the authors used commercially available, commonly consumed snacks, to which they mention they were unable to tightly control macronutrient QUALITY (i.e chocolate had more saturated fat, simple carbs compared to the crackers).


A higher protein, greek yogurt-style afternoon snack is better for appetite control compared to chocolate and crackers!

Keep in mind that these snacks were very simple (I for one like to have a combination of macronutients for snacks, like a protein PLUS a carb or a fat – i.e. greek yogurt mixed with something). Also, it was interesting to me that post snack fullness was not significantly different between the yogurt and cracker groups. Overall, I would say if you’re just looking for something simple to snack on to keep you full until dinner (and make you eat less at dinner time!) it looks like greek yogurt is the winner here!

2014-12-09 13.01.32

Citation: Ortinau LC, Hoertel HA, Douglas SM, Leidy HJ. Effects of high-protein vs. high- fat snacks on appetite control, satiety, and eating initiation in healthy women.Nutrition Journal 2014;13(1):97. doi:10.1186/1475-2891-13-97.

Bring on the Peanut Butter (Low Carb vs. Low Fat Diet Results)

Time for some more science! Today I will be summarizing an article entitled

A Lower-Carbohydrate, Higher-Fat Diet Reduces Abdominal and Intermuscular Fat and Increases Insulin Sensitivity in Adults at Risk of Type 2 Diabetes

In this study, authors evaluated fat loss in 69 overweight/obese men and women aged 21-50 years assigned to 1 of 2 diets, and 30 women with polycycstic ovary syndrome (PCOS) assigned to both diets with a crossover design.

Overweight/obese adults

The authors included ONLY African American or European American overweight/obese people without diabetes and whose weight hadn’t changed more than 2.3kg over the past 6 months. They excluded participants who exercised more than 2 hours/week, smoked, were pregnant or breastfeeding, or using any medication that could affect body composition (including hormonal birth control).

For the first 8 weeks, participants were assigned to 1 of 2 eucaloric (meaning they were intended to be at maintenance calorie intake – not intended for weight loss/gain) diets . We’ll call this the maintenance phase.

1) 55% carbohydrate, 27% fat, 18% protein

2) 43% carbohydrate, 39% fat, 18% protein

For the second 8 weeks, total calorie intake was decreased by 1000kcal/day, while macronutrient balance was maintained. This will be the weight loss phase

The two groups were compared in terms of body fat mass,  fat around the midsection, and markers of inflammation


On fat mass/ fat around the midsection

In the maintenance phase

Participants in the lower carbohydrate group lost significantly (11%) more fat around the midsection, even when adjusted for starting levels of fat mass!

In the weight loss phase

Participants in the lower carbohydrate group lost significantly more (4.4%) fat mass than patients in the low fat group. Again, this is while adjusting for initial fat mass levels.

At the end of the full 16 weeks, participants in the low carbohydrate group lost approximately 6kg (or ~13 pounds), compared to 4kg (~8 pounds) in the low fat group. Keep in mind that this is only 4 weeks of caloric deficit.

On markers of inflammation

No change was observed in either group, for either phase on markers of inflammation


The results were not different between ethnic groups (meaning both African Americans, and European Americans experienced the same effects – more fat loss in the low-carbohydrate group)

Women with PCOS

The authors included only women diagnosed with PCOS between 21-50 years with a super obese BMI (greater than or equal to 45). Other inclusion/exclusion criteria were the same as above.

The women were assigned to one of the two diets for 8 weeks,  followed by a 4 week washout period (participants were not assigned to any specific diet and were not given any specific foods), and then assigned to the opposite diet for another 8 week period.


While in the low-carbohydrate phase, participants lost significantly more fat around the midsection and fat mass compared to the low-fat phase (while adjusting for initial fat mass and change in lean mass). Also interesting: while in the low fat phase, participants lost significantly more lean body mass (read:muscle mass) compared to the low-carbohydrate phase.

Limitations of this study include the exclusion of participants with diabetes, taking hormonal birth control and other ethnicities, which could have made up a large portion of the population untested.

Additionally, for the PCOS study cross over design, they did not report the what participants ate during the washout period, which could have contaminated the results (for example, if participants were assigned to the low-carbohydrate group in the first phase, it is possible that they could have eaten a ton of carbs during the washout period – after restricting them – which could have resulted in lower fat loss in the second phase of the study).

Authors also did not record participant activity level throughout the study, which could have confounded the results, and although food was provided for the duration of the study (which is a big strength in these types of studies!), they did not specify where participants were getting their macronutrients from (i.e. carbs from fruits/veggies vs. chips, protein/fat sources).


It looks like restricting carbohydrate composition is more effective in terms of fat loss compared to restricting carbohydrates, even while maintaining your daily calorie intake!

But remember – this isn’t evidence for eating whatever you want as long as it’s low in carbs and high in fat. A lot of other factors do contribute to weight/fat loss in the general population, including total calorie intake, exercise, metabolism, size, etc. It should also be noted that the percentage of carbohydrate intake even in the low-carb group was not extreme. We’re not talking ketosis here – just watching overall carb intake and not restricting good fats. 

If you’re looking to lose weight make sure you’re eating mostly fruits and vegetables as your carbohydrate sources, and don’t be afraid to eat a little peanut butter (or avocado, or nuts, or olive oil)!

Citation: Gower, B. A. and A. M. Goss (2015). “A lower-carbohydrate, higher-fat diet reduces abdominal and intermuscular fat and increases insulin sensitivity in adults at risk of type 2 diabetes.” J Nutr 145(1): 177s-183s.

Weight Training and Aerobic Exercise to Attenuate Fat/Weight Gain while Aging

Here is a recently published article in the “Obesity” Research journal.

The authors report waist circumference and body weight in 10500 healthy U.S men (average age 58) followed through biennial questionnaires from 1986.

This cohort recorded dietary intake via a 131 item self reported food frequency questionnaire.

In 1996 and 2008, the participants were also asked to report the average time spent per week doing various exercise activities (walking, jogging, running, bicycling, tennis, swimming, squash, calisthenics, rowing, cardio machines, weight training, heavy outdoor work) and time spent watching TV.

  vs  vs 

Participants that were unable to walk, had experienced heart attacks, stroke, angina, diabetes or cancer were excluded from analysis.

Additionally, alcohol, sugar-sweetened beverage, fiber, trans-fat, and protein, and anti-depressant intake were included as covariates in a regression analysis to ensure any changes observed were due to activity alone (these specific foods have been shown to have an effect on weight gain)


As the amount of time spent weight training increased, the amount of waist circumference change decreased (i.e, more time spend weight-training = less age-related weight gain). The highest reported dose was associated with the least waist circumference change, and was defined as greater than 25 minutes/day. That’s not even one full TV show!

Additionally, the authors compared the results of weight training to that of other (aerobic) activities. The amount of waist circumference change was significantly smaller for the weight training model compared to any other activities. 

Additionally, weight training was beneficial for waist circumference change regardless of whether the participant adhered to the aerobic activity guidelines of 30 minutes/day 3 times a week.

While weight training did not significantly affect body weight, aerobic activity was associated with less body weight gain!

Obviously, the self-reported nature of this study has flaws (participants could be lying about their activity levels, intakes etc). Additionally, the authors did not measure body composition (% lean body mass vs. % fat mass), and the exclusion criteria make these results only generalizable to healthy males.

Even so, I think this goes to show that weight training ( even just a small amount) is very important as the population ages to ensure the maintenance of muscle mass and body composition, while aerobic activity is important to attenuate weight gain!

So I encourage you all to continue weight training AND aerobic exercise. And if you haven’t started yet, there’s nothing stopping you! I am a certified personal trainer, and if you’re looking for some tips to become more active, shoot me an email!


Have a great week everyone!

Citation: Mekary, R.A., Grontved, A., Despres, J.P., De Moura, L.P., Asgarzadeh, M., Willett, W.C., Rimm, E.B.,Giovannucci, E., Hu, F.B. Weight training, aerobic physical activities, and long-term waist circumference change in men. Obesity (Silver Spring) 2014. Epub ahead of print

Another Reason to Eat Blueberries


Here is a study showing that dietary flavonoid intake in midlife is associated with healthy aging in women.

Basically, it’s a large prospective cohort of over 13,000 women with no major chronic diseases.

Authors collected initial data in the 1980’s (when these women were in their 50’s), and gathered information on various aspects of aging and intake of flavonoids (a nutrient/ type of antioxidant found in blueberries, parsley, dark chocolate, bananas and citrus fruit) via  food-frequency questionnaire.

Of the women to survived until over 70, those with highest flavonoid intakes had greater odds of healthy aging (measured by mental, physical and cognitive function, and if the participant was free of major chronic diseases)

Also worth noting is that they performed a logistic regression analyis, which controls for variables that may alter the results (such as socioeconomic status, age, marital status, bmi, family history of disease etc.

Citation: Samieri, C., Sun, Q., Townsend, M.K., Rimm, E.B., Grodstein, F. Dietary flavonoid intake at midlife and healthy aging in women. Am. J. Clin. Nutr. 2014 100 (6) 1489-97.