Rugby Union Pre-Season Nutrition (Part 2): Monitoring Body Composition


Tracking body composition throughout the pre-season period is a useful strategy to evaluate the progress of your current strategy, which can then inform whether any additional intervention is required. At a minimum you should be assessing your body composition at the beginning of pre-season (baseline) and at the end of pre-season, which will then provide feedback upon your pre-season training block. Numerous body composition assessment methodologies are available, some better than others. When choosing a tracking methodology it is important to consider both the validity and reliability of the approach:

Basically, does your method accurately report your body composition, and can you consistently implement this test throughout pre-season to track progress. Now that you are aware of what you are looking for, let’s take a look at the typical methodologies utilised to measure body composition progress:

(1) Scale weight

This is one of the most common methods of tracking progress and certainly does have its place. However, it is important to appreciate that this method can only report body mass, and does not provide data upon fat mass or fat-free mass (i.e muscle). Therefore, it is only telling us part of the picture.

If incorporating this methodology it is important to standardise your approach. Best practice would be to weigh yourself upon waking following first morning urine void wearing similar clothing each time e.g. underwear only. Log your AM weight each morning for the week and then take an average. If you are weighing yourself during the day your data can be influenced by dietary/fluid intake and activity/exercise induced fluid loss. If weighing in and out of your gym sessions to track your body mass progress, the feedback you are receiving is not a true reflection of progress, as the data will merely be based upon fluid changes, and not muscle/fat gain or loss.

It is worth nothing that in tandem with scale weight, some individuals may opt to incorporate circumference measurements. Common sites measured include: arm (relaxed), arm (flexed), chest, waist, hips, thigh and calf. Although this too cannot differentiate between fat and lean mass, it can be interpreted along with body mass to provide further feedback upon progress.

(2) Bioelectrical Impedance Analysis (BIA)

This a quick test that is typically available in most commercial gyms or via integrated bathroom scales. You simply step on scale sensors or/and hold handles with additional sensors. This would then predict body fat based upon an electrical current passed through the body. This is based upon the theory that fat mass contains low amounts of water and fat-free mass (e.g. muscle) contains greater amounts of water. Therefore:

1) The greater the amount of fat, the greater the resistance to the electrical current.

2) The greater the amount of fat-free mass, the lower the resistance to the electrical current.

However, there are numerous limitations with regards to this method that should be considered before incorporating within your strategy.


Although this test can be quick, non-invasive and inexpensive (if you don’t have to buy a set of scales), it can be hard to standardise your approach due to dietary/fluid/activity influence upon results – especially if you do not have access to a nutrition professional or laboratory/researcher assistance.

(3) Skinfolds

This is one of the most common methods amongst athletic individuals, with subcutaneous fat thickness measured via callipers at different locations over the body following ISAK protocol (a standardised protocol utilised within scientific research and within applied practice by sport practitioners).

ISAK protocol sites (landmarks) of measurement include:

  • Bicep
  • Tricep
  • Subscapular
  • Illiac Crest
  • Supraspinale
  • Abdominal
  • Thigh
  • Calf

Skinfold testing is a 2 compartment method, which estimates fat mass and fat-free mass based upon the assumption that water, protein and mineral content are constant. This is therefore considered an indirect method, which provides an estimate of body fat via prediction equations based upon the data collected. However, caution is urged when interpreting the body fat % generated via the equation chosen, as equations used to estimate body fat % are population specific (age, ethnicity, gender or training status). Additionally, this approach only measures sub-cutaneous fat and does therefore not directly measure other fat storage sites. Data can be interpreted in combination with circumference measurements to give further insight into progress. Additionally, I would encourage the individual to focus upon the total sum of 8 skinfolds (millimetres) and use this to track progress, as opposed to body fat % prediction equations, which as I discussed are population specific and have their limitations.

I would also like to briefly address skinfolds and hormonal profiling, which is popular within the fitness industry. This is not a method that I would recommend, based upon that it has no scientific evidence to support it’s use. To measure an individuals hormonal profile would require clinical testing and the expertise of an endocrinologist. There are further limitations to skinfolds and hormonal profiling, which are beyond the purpose of this article. I would therefore advise to utilise an ISAK accredited individual if you wish to integrate skinfolds as a body composition monitoring strategy.

(4) Dual Energy X-Ray Absorptiometry (DEXA)

This is a criterion measurement technique originally developed for bone analysis. Subjects lie flat while two x-ray beams (one high and one low intensity) pass through the body and measure tissue x-ray absorption with scans typically lasting up to 15-20mins. As this is a three compartment method, data is provided regarding: fat mass, lean mass and bone mineral content.

This approach is considered one of the most valid and reliable methods of body composition testing and is often utilised within professional rugby to track changes of elite athletes (testing typically taking place pre and post season – some clubs may add mid-season testing). However, it is important to limit technical error and biological (day to day) error. Therefore, if implementing DEXA it is important to standardise your approach to allow the detection of small, but worthwhile changes in lean body mass and fat mass.

To limit technical error consider subject preparation, positioning, machine and analysis software. With regards to biological variation standardise by conducting testing in fasted state and a standardised state of hydration/bladder voided. Consideration should also be given to the timing of exercise, due to exercise induced fluid shifts . Therefore testing should take place prior to any training. Finally, intramuscular solutes such as glycogen and creatine, which also have bound water, can influence the lean mass data.

Methods such as Air Displacement Plethysmography (BOD POD) and Hydrodensitometry (Underwater Weighing) are also other body composition tests. However, due to the practicalities of requiring laboratory assistance, and with alternative methods available, I shall not cover these further.

Practical Application:

Okay so we have covered the common methodologies utilised to assess and track body composition. Now let’s put this all together into a strategy which you can implement during pre-season:

Option 1: Basic

  1. Scale Weight (daily): Weigh yourself in the morning following first morning urine void in minimal clothing. Take an average for the week.
  2. Circumferences (every 2-4 weeks): Arm (flexed and relaxed), chest (optional), waist, hips, thigh and calf. Ideally conduct this testing in a fasted and rested state (no exercise prior).

You don’t have to get fancy. Keeping it simple can be as equally effective. If you don’t have access to an ISAK accredited skinfold practitioner or DEXA facilities then simply keep a track of the above.

Option 2: Advanced

  1. Scale Weight (daily): Weigh yourself in the morning following first morning urine void in minimal clothing. Take an average for the week.
  2. Circumferences (every 2-4 weeks): Arm (flexed and relaxed), chest (optional), waist, hips, thigh and calf. Ideally conduct this testing in a fasted and rested state (no exercise prior).
  3. Skinfolds* (every 4-6 weeks): ISAK protocol – Track the sum of 8 skinfolds (mm) to inform progress. Ideally conduct this testing in a fasted and rested state (no exercise prior). Some individuals may wish to conduct skinfold testing more frequently, however I personally believe in allowing some time to see change. Also, by using the two other monitoring systems above this can provide additional feedback to support the process and inform decision making . For example, weekly skinfold testing may show small or no change, which can be demotivating for the individual. 

*Option to substitute out skinfolds for DEXA scan. However, due to the cost of a DEXA scan and the requirement for a laboratory or clinical setting, I would suggest to opt for skinfolds. If incorporating DEXA I would utilise this at the beginning and end of pre-season.

To help you monitor body mass/composition throughout pre-season I have created a monitoring spreadsheet (click here to download).

Over the first two articles of this pre-season nutrition series we have set out goal expectations, rates of progression and how to monitor/track body composition progression. In part 3 we shall begin to discuss the construction of daily dietary intake, with a focus upon the goal of muscle gain.


Looking to optimise your nutritional approach this pre-season? Our professional advice can help individualise your approach.

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