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Strength training: time for vertical thinking
Can lower body strength training affect upper body strength and vice-versa? SPB looks at new research on this topic, discusses the practical implications for athletes, and makes training recommendations
As we’ve discussed in previous SPB articles, one of the key requirements for producing and effective and efficient training stimulus is training specificity. The principle of training specificity suggests that for maximum fitness and performance gains, the type of training an athlete undertakes should replicate the movements/locomotion/pattern of muscle use required in his/her actual sport as closely as possible. This explains why runners need to perform running training (and not focus on other training modes such as cycling/rowing etc) to run well in competition. Likewise, cyclists should primarily cycle and swimmers primarily swim etc.
Transfer of training effect
Although specificity is a key aspect of a training program, there’s also something else at play - the so-called ‘transfer of training’ effect. In a nutshell, although two different modes of exercise induce two different sets of specific adaptations in the working muscles, there is a degree of overlap. So for example, runners who cycle, swimmers who row, cyclists who cross-country ski etc can expect a reasonable degree of performance benefit when adding or substituting another form of training – so called cross training – into their training program.
However, this is not the only transfer of training effect at play, particularly when it comes to strength training. As Andrew Sheaff explained quite recently in his article on injury rehab and the transfer of training effect, there’s some evidence for a ‘cross-education effect’ in strength training, where training one limb results in improvements in strength in the opposite limb(1). This effect might be relevant for athletes unable to train an injured limb, and where training the non-injured limb could be a powerful tool for helping athletes recover from injury and return to sport safely.
Understanding the cross education effect
How is it possible that training muscles on one side of the body can produce strength gains on the other untrained side? Although the cross education effect in strength training is poorly understood (and indeed, remains a somewhat controversial theory among some researchers), the current consensus of thinking is that there are two prime reasons for this effect:
· Neurological – when training one side of the body, powerful neural impulses are generated, which travel from the motor cortex in the brain to the motor neurons, and from there to the activated muscle fibres. However, it is likely there is some ‘spill-over’ of these neural impulses from the motor neuron pool to other muscle fibres, meaning that they also undergo a small degree of activation(2,3). This effect may translate into longer-term strength improvements on the account of an ‘intensified central neural drive’(2).
· Hormonal – During vigorous training, the endocrine system secretes a number of hormones, which enter the blood stream and can then favorably stimulate different tissues such as muscle and motor neurons all over the body, regardless of whether those tissues underwent training(4-6). Recent research suggests that these hormonal changes contribute to strength improvements of the untrained muscle groups in older adults(7).
The lower-upper body cross-education effect
So far, we’ve talked about cross-education effects in terms of left/right side strength training and non-specific endurance training adaptations. However, some researchers have speculated that there could be a blend of these effects, especially in terms of upper-lower body transfer. One possibility is that upper-body strength training in runners could help develop leg strength, and help retain muscle fiber volume - ie preserving their size from decreasing after long running sessions(8). This could potentially lead to improved leg power without the need for undertaking tiring leg-strength training sessions(9). Likewise, resistance training of leg muscles may lead to strength improvements in upper extremities, which could benefit athletes where upper body strength and power are important for success.
To date, there’s been even less research into these upper-lower body cross-education effects than left side/right side effects. Part of the reason for this lack of data is that are just so many of exercise variations and permutations in which upper body and lower body exercises can be used. In addition, very few studies to date have looked at how upper-body and lower body strength and endurance training interventions impact each other. But now a new study has carried out a review of all the previous research on this topic, with an emphasis on upper-lower body cross-education effects (so-called ‘vertical strength transfer’)(10).
New research
In this study by British scientists, and which was published last month in the journal ‘Sports Medicine’, the researchers set out to compile and analyze all the data from previously published research on vertical strength transfer effects, and to understand how training of one body region – for example the lower body – can affect adaptations in distant body areas (ie the upper body). In addition, they also sought to understand how different upper and lower body exercise protocols affect the induced training adaptations of either region.
To do this, the researchers scoured the scientific databases for studies that met the following strict criteria:
· Studies looking at concurrent lower body endurance training combined with upper body resistance exercise, and the effects on lower body muscle adaptations (ie leg muscle size, strength and power).
· Studies looking at lower body resistance exercise training on upper body muscle size, strength and power, trained during the same time period.
· Studies investigating lower body resistance exercise training on untrained upper body strength or vice-versa.
In addition, studies were excluded from the review if they:
· Paired lower body endurance training (running or cycling) and upper body resistance exercise without examining lower body adaptive potential.
· Had an insufficient duration (under 5 minutes) of the lower body endurance protocol (ie running or cycling) to be considered an independent exercise session – for example if the lower body endurance protocol was simply a pre-workout warm up.
· Focused on a unilateral training adaptation, and only looked at the left-right cross-education phenomenon.
· Applied an exercise intervention that did not distinguish between the two body segments (eg weightlifting exercises working both the lower and upper body together).
· Applied an exercise intervention that was not standardised between the training groups.
These exclusions meant that the overall findings would be highly specific to the vertical strength transfer effect and relevant to the first three criteria.
Overall, 5242 articles were screened and out of these, just 24 studies met the inclusion criteria above. These were as follows (click on the link to see details of all the studies in each category):
· Vertical strength transfer effects between upper body resistance exercise and running or cycling session - table 1.
· Vertical strength transfer effects between upper body resistance exercise and lower body resistance exercise - table 2.
· Vertical strength transfer effect with the exercise of one body segment - table 3.
What they found
Upon careful collating and analysis of the data from these studies, several key findings emerged. These were as follows:
· Combined upper body strength and lower body endurance training (ie running or cycling) seems to stimulate adaptations in both regions, resulting in improved lower body muscle strength and size, particularly in older athletes. In short, upper body resistance training can help develop or protect leg muscle strength, preserving power-generating capacity, even when no lower body strength training takes place.
· Strength training the legs using high-volume, lower rep resistance exercises (or using BFR resistance training – see here) can help produce strength improvements in previously or subsequently trained upper body muscles (chest, back, shoulders arms). This beneficial effect is also apparent when the whole body is trained in the same workout. Athletes who need upper body strength and power should therefore not neglect leg training, providing they use higher-volume, lower-load sessions.
· High-volume upper body resistance training seems to beneficially affect hormone receptor response in leg muscles that are subsequently trained. When training for leg strength therefore, some high-volume, low-load upper body strength training carried out first might confer an additional advantage.
Practical implications for athletes
Given the evidence for the left-right cross education effect, it’s perhaps not surprising to discover there’s a significant upper-lower body vertical strength transfer effect. As an athlete, you can use this information to help improve your training sessions and as a strategy to help in the event of an injury. Starting with the latter, should you be unfortunate to sustain an injury, strength training the ‘other’ end of the body should be considered a useful strategy to help maintain strength in the injured limb(s). For example, in the case of an injured runner who needs to stay off his/her feet for a couple of weeks, engaging in upper body strength training may help minimize strength losses in the injured and the uninjured leg.
For athletes who suffer an injury in the upper body – eg a swimmer who sustains a shoulder injury – training the lower body using high-volume, high rep training is a worthwhile way of maintaining upper body strength. This lower body training can also take the form of BFR training, which requires less loading. If using BFR, the recommendation is that around 60% or so of 1RM will produce significant training benefits while allowing the muscles more time to recover from harder, non-BFR training sessions.
More generally, the vertical strength transfer effect can be applied to all athletes seeking to maximize performance. For endurance runners and cyclists who may be already performing some lower body strength training to improve running and cycling economy, be aware that adding in some upper body strength work can create an additional strength stimulus. The same is true for other sports such as swimming and kayaking, where upper body strength is important; these athletes should be sure to perform some lower body training using higher-rep, higher-load but lower intensity sets of leg exercises (squats, leg presses, lunges etc). Where developing leg strength is key, there may be additional benefits from carrying out upper body training first, quickly followed by lower body strength training. The final point to emphasize is that the vertical transfer effect seems to occur with a greater magnitude as the years pass, which makes its use by older athletes especially appealing!
References
1. J Sci Med Sport. 2023 Aug;26(8):440-445
2. Physiol Rev. 2001;81:1725–89
3. J Strength Cond Res. 2024;38(2):342–9
4. Front Physiol. 2021;12: 656455
5. Am J Physiol Endocrinol Metab. 2009;297:157–64
6. Nutr Metab. 2022;19:52
7. Mech Ageing Dev. 2020;185: 111190
8. J Appl Physiol (1985). 2006;101(3):721–7
9. J Appl Physiol. 1995;78:976–89
10. Sports Med. 2024 May 14. doi: 10.1007/s40279-024-02039-8. Online ahead of print
Andrew Hamilton
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