Got your arm in a cast after a skiing accident? Here’s how you can maintain your strength and muscle mass

Ein Verschneider beim Skifahren, den Faceplant mit den Armen zu verhindern versucht und schon ist es passiert: Der Rettungsdienst diagnostiziert einen gebrochenen Arm und das folgende Röntgenbild bestätigt den Verdacht. Instead of enjoying the sun slowly setting behind the mountains on your final descent into the valley, you’re deciding what colour your cast should be. This isn’t a horrific scenario only for very sporty people. After all, an immobilised arm that’s lost strength and muscle mass is painstaking to rebuild for anyone. So, can this be prevented?

Muscles are a storage organ that generate power and communicate with other organs. If they’re not used, they lose mass and strength. This is well documented and most notably seen in the case of limbs being immobilised after joint surgery [1], prescribed bed rest [2] and prolonged stays in outer space [3]. Already 5 days of immobilising one leg reduces the maximum voluntary torque of the knee extensor by nearly 10%, and the cross-sectional area of the quadriceps decreases by approximately 4% [4]. Over longer immobilisation periods of 4 to 6 weeks, even greater muscle mass losses are observed. For example, the cross-sectional area in the flexor and extensor muscles of the elbow decreases by 11% [5], or 20–32%, respectively [6], and by 16% in the extensor muscles of the knee [7].

The cross-education effect

In 1894, Edward Scripture, along with Theodate Smith and Emily Brown, published a study titled «On the education of muscular power and control» [8]. The two co-authors were also the study’s only participants. Brown trained her muscular power (strength training), while Smith trained her muscular control (technique training). Training was performed with one arm at a time and lasted 9 and 10 days, respectively. In both the trained and untrained arm, strength improved by 40% and 25%, respectively. It was the first work to identify what’s known as cross education, that is, a bilateral improvement in performance due to unilateral training.

How exactly this mechanism works remains unknown. However, there are two main hypotheses to explain how neural adaptations may lead to cross education [9,10]. The first is that unilateral strength training may activate neural circuits that alter the effectiveness of motor pathways and are projected to the untrained limb. The second hypothesis is that there are adaptations in motor brain regions that play a specific role in controlling movements in the trained limb, which the untrained limb can access during voluntary, high-intensity contractions.

Either way, we can use this mechanism to our advantage – and there are already many studies on the subject. The most recent study addresses the hypothesis that single-arm strength training could mitigate the extent of muscle damage in an immobilised arm when eccentric exercises are performed after immobilisation [11]. Chen and his team, who conducted the study, recruited 36 healthy young men who then had their nondominant arm immobilised for 3 weeks. They were divided into 3 groups of 12 subjects: a control group, an eccentric group and a concentric group. During the 3-week immobilisation period, the eccentric and concentric groups trained their elbow flexor twice per week. The control group didn’t exercise. Each workout consisted of 5 sets of 6 purely eccentric or purely concentric contractions using a dumbbell. The load was increased from workout to workout, starting at 20% of the maximum isometrically producible force and reaching 80% toward the end of the study. Strength was measured each week for both groups. After the study, all subjects did 5 sets of 6 repetitions each at their maximum isometric force they could generate with their immobilised arm.

Results

By the time immobilisation ended, the control group that hadn’t exercised experienced a loss of strength of over 20% in the immobilised arm. In the «one-armed, purely concentric training» group, the loss of strength was only 4%, and in the «purely eccentric training» group, a strength gain of 3% was measured in the immobilised arm.

Now for the muscle cross-sectional area: in the control group, the cross-sectional area in the immobilised arm decreased by 14%. In the eccentric group it remained constant, while in the concentric group it decreased by 4%.

The 30 eccentric contractions in the immobilised arm resulted in severe muscle soreness in the control group, caused by muscular injuries. At the molecular level, markers of muscle soreness were still significantly elevated up to 5 days after the end of the study compared with the other two groups. The eccentric group displayed the most protection against muscle soreness. Eccentric training had a protective effect in the immobilised arm, leading to an 83% reduction in muscle soreness compared to the control group. For the concentric training group, the protective effect was 43%.

So, depending on the severity of the injury, an immobilised arm or leg doesn’t have to mean that a training season must be cut short or that your goal can’t be achieved. You can take advantage of the cross-education effect and train unilaterally. Eccentric training appears to produce a greater advantage compared to concentric training. But both have significant benefits compared to no training at all. In short, you can use unilateral strength training to mitigate the loss of strength and muscle mass caused by immobilisation due to injury.

References

1. MacDougall JD, Ward GR, Sale DG, Sutton JR. Biochemical adaptation of human skeletal muscle to heavy resistance training and immobilization. J Appl Physiol Respir Environ Exerc Physiol. 1977;43: 700–703. doi:10.1152/JAPPL.1977.43.4.700

2. Berg HE, Dudley GA, Haggmark T, Ohlsen H, Tesch PA. Effects of lower limb unloading on skeletal muscle mass and function in humans. J Appl Physiol. J Appl Physiol (1985); 1991;70: 1882–1885. doi:10.1152/JAPPL.1991.70.4.1882

3. Edgerton VR, Zhou MY, Ohira Y, Klitgaard H, Jiang B, Bell G, et al. Human fiber size and enzymatic properties after 5 and 11 days of spaceflight. doi.org/101152/jappl19957851733. American Physiological Society; 1995;78: 1733–1739. doi:10.1152/JAPPL.1995.78.5.1733

4. Wall BT, Dirks ML, Snijders T, Senden JMG, Dolmans J, Van Loon LJC. Substantial skeletal muscle loss occurs during only 5 days of disuse. Acta Physiol. John Wiley & Sons, Ltd; 2014;210: 600–611. doi:10.1111/APHA.12190

5. Yue GH, Bilodeau M, Hardy PA, Enoka RM. Task-dependent effect of limb immobilization on the fatigability of the elbow flexor muscles in humans. Exp Physiol. John Wiley & Sons, Ltd; 1997;82: 567–592. doi:10.1113/EXPPHYSIOL.1997.SP004048

6. Vandenborne K, Elliott MA, Walter GA, Abdus S, Okereke E, Shaffer M, et al. Longitudinal study of skeletal muscle adaptations during immobilization and rehabilitation. Muscle Nerve. Muscle Nerve; 1998;21: 1006–1012. doi:10.1002/(sici)1097-4598(199808)21:8<1006::aid-mus4>3.0.co;2-c

7. Hather BM, Adams GR, Tesch PA, Dudley GA. Skeletal muscle responses to lower limb suspension in humans. doi.org/101152/jappl19927241493. 1992;72: 1493–1498. doi:10.1152/JAPPL.1992.72.4.1493

8. Scripture EW, Smith T, Brown E. On the education of muscular power and control. Stud from Yale Psychol Lab. 1894;2: 114–119. Available: echo.mpiwg-berlin.mpg.de/ECHOdocuView?url=/permanent/vlp/lit23174/index.meta%0A physiology.org/doi/10.1152/physrev.2001.81.4.1725

9. Lee M, Carroll TJ. Cross education: Possible mechanisms for the contralateral effects of unilateral resistance training. Sport Med. Adis International Ltd; 2007;37: 1–14. doi:10.2165/00007256-200737010-00001

10. Ruddy KL, Carson RG. Neural pathways mediating cross education of motor function. Front Hum Neurosci. Frontiers Media S. A.; 2013;7: 397. doi:10.3389/FNHUM.2013.00397/BIBTEX

11. Chen TC, Wu S-H, Chen H-L, Tseng W-C, Tseng K-W, Kang H-Y, et al. Effects of Unilateral Eccentric versus Concentric Training of Non-Immobilized Arm During Immobilization. Med Sci Sports Exerc. 2023; doi:10.1249/MSS.0000000000003140