Exercise, Hypertrophy

February 3, 2014

New Study: Bodybuilding-Type Training Increases Intracellular Water Content

I recently co-authored a new study that investigated increases in intracellular hydration following performance of 16 weeks of bodybuilding-type resistance training. I am pleased to say that the study — a collaboration with colleagues at Londrina State University in Brazil — has just been published in the European Journal of Sports Science. Here is a summary and what to take home from the findings.

The Background:
It has been well-established that regimented resistance training results in increases in muscle hypertrophy (i.e. growth). The mechanical forces associated with lifting cause an adaptive response that results in increases in the contractile elements (actin and myosin) as well as structural proteins of muscle. These adaptations ultimately facilitate the muscle to be able to exert greater amounts of force. It’s a basic adaptive response to a stress (i.e. a survival mechanism) that makes us stronger so we can handle similar future events if and when needed.

There has been extensive debate as to whether resistance training also increases non-contractile (sarcoplasmic) hypertrophy. Non-contractile elements include things such as collagen, organelles, and fluid. The fluid component is one of the more intriguing areas of discussion. It’s no secret that resistance training can have an effect on altering intramuscular water — the “pump” is a well-known phenomenon in bodybuilding-type training. But what remains unclear is whether resistance training can increase intracellular water chronically over time. Our study sought to shed light on this topic.

What We Did:
A total of 64 college-aged subjects (30 men and 34 women) participated in the study. Subjects engaged in a supervised progressive resistance training program carried out 3 non-consecutive days a week over 16 weeks. Training consisted of a bodybuilding-type routine whereby 3 sets of 8-12 reps were performed with 60-90 seconds rest between sets. A total of 11 exercises were performed per session using a combination of free weights, cables, and machines. All sets were taken to the point of momentary muscular failure.

Bioelectrical impedance spectroscopy (BIS) was used to measure total body water, intracellular water and extracellular water content. BIS is a validated tool for measuring body water and its various sub-fractions. Assessments were made at baseline, the mid-point of the study, and at study’s end.

The Results:
Intracellular water was significantly increased following training in both men and women. The effect size — in simple terms, a measure of the magnitude of results that takes into account variance between subjects — was considered moderate, indicating the results are meaningful. Both men and women showed approximately equal responses as to increases in intracellular water over the course of the study.

Practical Implications:
As noted, this study provides compelling evidence that regular bodybuilding-type resistance training leads to a chronic increase in intracellular fluid status. Why should anyone care about increasing the water content of muscle? Well, there is a large body of research showing that cell swelling via increased intracellular hydration results in marked increases in protein synthesis and reductions in protein degradation; a hypertrophy homerun. These findings have been shown in a wide variety of cell types, implying that keeping muscle fibers hydrated may actually increase contractile hypertrophy and thus enhance strength.

Now it’s important to note that these observations are from in vitro (i.e. test tube) data. Whether similar results play out in practice in hard-training lifters is still unknown and need further study. That said, the aforementioned findings certainly suggest that there may well be an anabolic effect (and in fact one of the hypotheses for hypertrophic effects of creatine is its role as an osmolyte).

What remains unclear is whether the increased intracellular hydration is specific to bodybuilding-type training or inherent with all types of lifting. We speculated that results of the current study may have been due to increased glycogen storage. Bodybuilding-type training relies primarily on fast glycolysis to fuel performance, whereby carbohydrate is the primary energy source (as opposed to powerlifting-type training, which relies primarily on the phosphagen system). As such, the body adapts by increasing its capacity to store glycogen. Since glycogen attracts 3 grams of water for every glycogen granule, it stands to reason that this was responsible for the increased hydration status.

What’s Next:
We are currently designing a study that will compare chronic changes in water sub-fractions following bodybuilding- versus powerlifting-type training. The hope is to begin data collection before the year is out. Stay tuned.

Reference:
Ribeiro AS, Avelar A, Schoenfeld BJ, Ritti Dias RM, Altimari LR, Cyrino ES. Resistance training promotes increase in intracellular hydration in men and women. Eur J Sport Sci. 2014 Jan 28. [Epub ahead of print]