Research Review: Attacking strength from all angles

Paper title: ‘Does Performing Different Resistance Exercises for the Same Muscle Group Induce Non-homogeneous Hypertrophy?’ Publication: International Journal of Sports Medicine. January 2021. doi: 10.1055/a-1308-3674 Publication date: January 13th 2021

Regardless of your sport, the evidence that strength training can enhance performance has now become irrefutable. As we have reported in previous Sports Performance Bulletin articles, sports scientists now understand that strength and its manifestations – power, speed, and muscle economy (how efficiently muscles work) -are more closely related to sports performance than any other quality. The benefits of strength training are not just relevant for sports involving power, speed and acceleration; numerous scientific studies have also demonstrated that strength training yields performance benefits even for pure endurance sport athletes such as distance runners and cyclist, triathletes and ultra-event athletes^(1-4).

Strength training program structure

Unless participating in strength training for its own sake, the goal of most athletes undertaking this mode of training is to derive maximum strength benefits (greater force production and power generation, improved resilience to injury, more efficient muscle energy production etc) in the minimum time. Unsurprisingly, optimizing strength-training program structure has been the subject of a great deal of research in recent years – research that we have reported on, including articles discussing order of exercises, optimum warm ups for strength, the optimum volume of strength work, optimum weight loading, and many more.

One strength-training variable that is rarely discussed is the effect of exercise variety when training a specific muscle region. For example, when training the thighs, is it better to hit the muscles with three sets of the same (homogeneous) exercise (eg squats) or is it better to vary (heterogeneous) the exercises in the three sets (eg 1 x squats, 1 x lunges and 1 x leg press)? Until recently, there’s been a dearth of data in the literature from which to draw conclusions. However, a newly published study by Brazilian scientists has compared the effects of homogeneous vs. heterogeneous strength exercises for a muscle group and come up with fascinating findings.

The research

In this study, researchers compared the effect of performing a number of the same or different exercises for a muscle group on resistance training sessions on muscle hypertrophy (growth) at different sites along muscle length. Why was muscle hypertrophy chosen as a measure of how effective each strength protocol was? Well, muscle hypertrophy is relatively easy to measure with a high degree of accuracy, and research shows that hypertrophy as a result of resistance training is directly correlated to strength, power and force gains (even though the precise mechanisms are poorly understood)⁽⁵⁾.

Twenty-two detrained men were chosen to participate – ie who had previously regularly resistance trained but who had ceased. The reasoning for choosing detrained subjects was that more significant gains (and thus more easily measureable) can be expected when a detrained individual retrains compared to a completely untrained subject commencing training, or one already in regular training trying a new protocol⁽⁶⁾. The subjects were split into two groups:

• Homogeneous resistance training - the same exercises performed on the quadriceps and triceps muscles in every training session.
• Heterogeneous resistance training - a variety of exercises (but the same overall number) performed on the quadriceps and triceps muscles in every training session.

All the subjects completed 27 training sessions; three weekly sessions for nine weeks. Before and after the 9-week program, muscle thickness was assessed at the proximal, middle, and distal sites of the lateral and anterior thigh, elbow flexors, and extensors by B-mode ultrasound (an accurate method for determining hypertrophy).

The findings

The key finding was that the heterogeneous group (ie those who trained the muscle groups with a variety of exercises) significantly increased muscle hypertrophy at all of the sites analyzed. This was in contrast to the homogeneous group, where gains in muscle hypertrophy were less marked, and were limited to the middle site of the lateral thigh and the proximal site of the elbow flexors.

Practical implications

Although this is just one study, the implication is that a given volume of resistance exercise consisting of a number of different exercises appears to produce a greater hypertrophic (and therefore strength) effects than the same volume of a single exercise repeated multiple times. Does this research fit with what we already know about stimulating muscle growth? Most likely, yes.

A 2019 study in the Journal of Applied Physiology examined the molecular biology surrounding the physiology of muscle growth following exercise⁽⁷⁾. In very simple terms, it concluded that mechanical loading in muscles is the key driver of muscle growth and adaptation after exercise. Furthermore, it seems that muscle fibers contain ‘mechanosensors’, to detect mechanical loading, and that these mechanosensors regulate gene activity related to muscle growth. However, once the mechanosensors in a fiber have been stimulated and activated, repeated stimulation (with the same exercise) is unlikely to generate additional stimulation. Hitting different fibers using a variety of exercises by contrast is likely to activate a larger number mechanosensors, resulting in a greater stimulus for adaptation. Although our understanding of this area is far from complete, the evidence that athletes training for strength should consider regularly varying their exercises for each muscle group is persuasive!

References

1. Phys Ther Sport. 2002; 3(2):88–96
2. Sports Medicine. 2016; 46(10):1419–49
3. British Journal of Sports Medicine. 2014; 48(11):871–7
4. J Sport Health Sci. 2015; 4:308–17
5. Eur J Appl Physiol. 2019 Jan;119(1):265-278
6. Exp Gerontol. 2020 May;133:110860. doi: 10.1016/j.exger.2020.110860
7. J Appl Physiol (1985) . 2019 Jan 1;126(1):30-43