[A couple of hours late, but better late than never!]
Last week I looked at an analysis of adherence to a strength training intervention in adult women. At the time I was looking at a study that was based on research done for a separate study, so I felt that it would only be right to complete the set by looking at that original study. I don’t think anyone reading this blog will be surprised by the results, but it is helpful to sometimes go back to basics and look at the things that we all know, inherently, to be true about our strength training work. A reminder that there really is a purpose to it, beyond how it makes us feel.
Strength training and adiposity in premenopausal women: Strong, Healthy, and Empowered study
Schmitz K H, Hannan P J, Stovitz S D, Bryan C J, Warren M, Jensen M D, American Journal of Clinical Nutrition 2007; 86(3):566-572. (Free copy of the study here.)
The purpose behind this study was to “assess the efficacy of twice-weekly strength training to prevent increases in percentage body fat and intraabdominal body fat compared with a standard care comparison group among women.” I have to say that they did a pretty good job of this.
On a separate note they also expressed an interest in finding out if the women also gained more confidence with physical activities in other areas of their life, such as recreation, household activities and transportation. (This last one confused me, but Chris told me that they probably mean carrying things about, like shopping. This hadn’t even crossed my mind – a clear sign that I’ve been doing weight training for too long now!)
While they expressed interest in finding out about this, no further mention is made about it in this study and I suspect that data considered through interviews and discussions with participants throughout the study is discussed and considered in a separate paper: Barriers and motivators for strength training among women of color and Caucasian women. O’Dougherty M, Dallman A, Turcotte L, Patterson J, Napolitano M A, Schmitz K H. Women Health 2008;47(2):41-62. Unfortunately I haven’t been able to find a free copy of this available on the internet so if anyone can get hold of a copy to send to me I’d really appreciate it. I think it might contain the answers to questions raised by several readers of last week’s paper too – how the study actually made the women feel.
It’s worth lingering for a moment on the criteria for inclusion and exclusion in this study as they advertised widely for participants and ended up with 1,721 women to screen for it. Of these 164 participants made it through all the criteria and were still participating by the time they were ready to start the study. I learned from last week’s study that several women gave the free two-year membership to a gym as one of the key reasons they were motivated to apply to join the study at the start and a test group of 164 women is a really large study when you compare it to most strength and conditioning research studies looking solely at women where the test group is more often about 20 women.
In order to be included in the study the women had to meet the following criteria (as a well as a few others I’ve excluded for brevity):
- Age 25-44 years
- BMI 25-35
- A stable bodyweight with less than 10% change in the previous year
- Have a sedentary lifestyle or, at most, three weekly sessions of moderate aerobic activity
- Not be participating in a weight-loss programme
- Not have any physician-diagnosed menstrual irregularities
- Not have any significant gynecologic conditions
- Not have any positive responses to the Physical Activity Readiness Questionnaire
- Not have participated in any strength training in the previous six months
- Not currently be or have recently been pregnant or lactating
- Not be taking one of a number of listed medication types (essentially knocking out women with certain conditions)
- Not have any plans to be away for more than three consecutive weeks during the two-year study period (I bet that condition made a lot of women suddenly have an urge for a really long holiday, simply because they couldn’t take one, even if they’d never done such a long holiday before).
It’s a long list of conditions but the purpose is clear. It drove the number of participants down from a huge number to a much smaller number of women who were, overweight or obese, largely sedentary, but otherwise in good health.
These participants were then split into two equal groups – the first undertook strength training, the second were left alone as a control group. The control group were not given any advice other than being mailed standard American Heart Association (‘AHA’) brochures recommending thirty minutes of moderate activity each day (such as walking). The results provide an interesting insight in itself about either the effectiveness of this advice or of how much notice is taken of this advice (although it isn’t entirely clear which is the more deficient).
I’m not going to go into huge detail about the training programme as I gave a lot of information about it last week. As a brief reminder, the participants were given a training programme involving two sessions a week – the first 16 weeks were supervised by personal trainers and then training continued unsupervised with a top-up group training session every 12 weeks to adjust the exercises that were being done. Having started these sedentary, previously untrained women on resistance machine exercises, free-weights exercises were apparently introduced over time, although the specific exercises used are not detailed, only the muscle groups they were targetting.
For the first year the training session lasted 60-90 minutes and involved nine common strength training exercises completed for three sets of eight to ten reps on each exercise, always lifting the heaviest weight possible. In year two participants were allowed, if they wanted, to drop down to two sets of each exercise. This is estimated as having reduced the length of the workout to 45 minutes. Essentially year two reflected a more maintenance-style programme.
I find it interesting that participants in this group were also asked to maintain throughout the study period whatever amount of aerobic activity they had been doing before the started the study entry. If they were already doing three lots of aerobic activity a week (the maximum possible under the criteria for participants) this would have meant quite a significant activity load once two strength training sessions were added to it.
Unsurprisingly, with a study of this size they wanted to maximise what they learned. Data was collected at the start as well as at the end of year one and the end of year two and they collected all sorts of data that may not have necessary seemed relevant at the time – this is why it has been possible to do so many other studies using the data collected during this study.
Clearly the main interest for this study was the body composition and, in particular the location of the fat, so the following information was collected:
- Body weight
- Body height
- Body composition, using dual-energy X-ray absorptiometry (DXA)
- Estimates of abdominal fat areas (total, subcutaneous and intraabdominal) using a single-slice computed tomography (CT) scan
- Muscle strength through a max effort bench press and leg press. This was tested twice at each data collection point, with a two week break between each test, so that the best possible effort could be measured and the best effort of the two was then used.
- Physical activity levels through a complex method of measuring threshold activity level through a treadmill test and then using an accelerometer for two weekdays and two weekend days to measure activity that was above this threshold “sedentary” level.
- Adherence to the strength training regime
- A diet history questionnaire (a food-frequency questionnaire), although it should be noted that participants were “asked not to make any changes in their diets that might result in weight or fat gain or loss. Seasonal variations in their diets were expected and allowed.”
- Interviewer-administered surveys for the demographical divisions and at which other information was also gathered about how the women were feeling and their thoughts on the study.
For this post I’m going to focus on two sets of results – the body composition and the strength gains. Interestingly all the data is given in terms of absolutes at the start of the study and then the amount of change seen in relation to this baseline. I looked at adherence last week and you might want to revisit that to remind yourself at how sharply adherence declined in year two, since it has some reflection in the results here.
Firstly, let’s look at the strength gains. Unsurprisingly the control group saw a decrease in upper body strength over the two years and this is at a fairly constant rate, however it is interesting that the control group also gained leg strength during the first year (before then losing half of it again in year two). I have no idea what caused this and the authors don’t seem inclined to consider it either. However, when this is compared to the gains in strength for the leg press in the training group there is a huge difference. The trained group saw a relatively huge increase in leg strength and a fairly large increase in upper body strength. Noticeably the strength measures for the trained group also drop off in year two. The authors sensibly put this down to a reduction in adherence to the programme in year two (adherence had dropped to 40-50% in many cases) and the fact that the programme had also moved from a strength gain programme to a maintenance programme. Of course, if someone was only attending half the sessions and was following a maintenance programme it seems logical that they might see a decline in strength, and I think that the reasoning for the strength declines put forward by the authors are reasonable, but it is pleasing to see that this drop-off in strength is not particularly marked in the lower body.
In fact, I think it is also worth noting the fact that while they seem able to retain a lot of the leg strength despite an apparent decline in training, the upper body strength declines much more rapidly. This is very much in line with what I saw in the gym, especially during my first few years of training when I was still a relative novice. Upper body strength just doesn’t seem to stick as well as lower body strength. Is this something that other women have noticed and is it specific to women or have other men noticed a more immediate decline in upper body strength when compared to lower body strength if they take a break from training?
Body composition measures are even more interesting and I’ll briefly discuss most of them in turn.
To start us off, body mass is fairly non-descript (though I’m not even going to touch BMI since I consider it a pointless measure). As is to be expected the body mass of the training group increases steadily, but the build up of new muscle tissue will have contributed to weight gain as well as any fat that they might have put on. A reminder to all new trainees that gaining weight doesn’t necessarily mean that the training isn’t working (after all, I now weigh 6kg more than I did a few years ago yet I definitely look and feel a lot better). It is perhaps interesting that the control group put on the weight much more abruptly in the second year, although the reasons for this are unclear.
Body fat movements tie neatly with the strength gains, fat mass and lean mass measurement. Those in the control group kept body fat appear to have swapped some body fat for lean mass in year one, since their body weight stayed the same but with a reduction in fat mass and gain in lean mass and reduction in body fat. Again, the reason for this isn’t clear, although perhaps some of them took some notice of that AHA brochure sent to them at the start of the study that advised them to do more moderate intensity exercise. However, in year two they put back on almost double the amount of fat mass that they lost in year one, so whatever they had done to lose it, this stopped working (or they stopped doing it) in year two. I’m intrigued that the lean mass doesn’t drop again though.
Moving over to the training group there is a much bigger reduction in body fat percentage with almost double the lean mass gains seen by the control group and a statistically significant reduction in fat mass when compared to the control group. Despite the adherence drop-off in training during year two that was so evident in the strength measurements, the lean mass mostly remained with the trainees, although body fat started to return in year two. Despite this, the body fat did return at a slower rate than the control group were putting it on, perhaps thanks to the additional muscle the trainees were carrying in year two.
Finally, looking at the composition of that fat, I was disappointed to see that after a promising start losing some of the intraabdominal fat, the trainee group gained a large amount of this in year two while gaining a lot less subcutaneous abdominal fat. This could be seen as a failure for strength training to work its magic until you compare it to both the adherence (poor in year two – if you want this to work you need to keep doing it) and to the control group. The control group’s intraabdominal fat levels sky-rocket in year two and this has ennabled the authors to reach their conclusion that there is a “potential for strength training to provide sustained obesity prevention benefits over time. These findings suggest that strength training is an efficacious mode of physical activity to expand the repertory of approaches available to women for the purpose of obesity prevention.”
Potential issues with the study
With a study of this size and complexity there are always going to be confounders. The study participants are humans and they cannot be closely monitored every minute of every day for two years. In particular diet was only loosely monitored.
While a dietary health questionnaire was completed at each test point, which showed that participants were seeing no significant change to their total calorific intake, there is no further detail in the study about whether the macronutrient composition of those calories of the timing of those calories changed over the two years. This is acknowledged but the authors and I feel it is only fair to let them express the problem with this in their own words:
“… the 2 most important potential confounders (diet and physical activity) did not show differences at any measurement time point. The measurement of physical activity by objective monitoring avoided the potential for desirability bias from self-report that may occur in intervention studies. No such objective monitoring of dietary changes was possible. Further, food-frequency questionnaires such as the DHQ may not be sensitive enough to capture changes in dietary pattern. The possibility that significant changes in dietary intake influenced the body composition results reported cannot be ruled out.”
A concluding thought
So there you have it, from the authors themselves. Some of the changes in the study could be due to dietary changes rather than due to the training. However, despite this I am inclined to the opinion that this study does provide some support for the belief that strength training on a fairly minor scale not only aids in supporting fat loss (when adhered to) but can also help prevent the natural abdominal fat gain that seems to occur over time in sedentary premenopausal women.
Overall I think it’s a helpful study. I really would like to get my hands on the article that looks at the women’s interviews and what they were really thinking as I believe it would make a huge difference to understanding the overall changes to the women and their adherence to the training programme over the two years. But even without that, I hope you’ve all found something to take away from the two studies I’ve looked at based on this data.
Next week I’ll see if I can find something about non-sedentary women and strength training!