Scientists Show a Promising Way to Reliably Assess Muscle Damage after Exercise

Scientists explore potential predictors for the symptoms of exercise-induced muscle damage in knee muscles

Muscle damage caused by exercise can lead to a variety of uncomfortable symptoms and, in the worst case, physical disability. Thus, having a reliable way of assessing muscle damage is essential to determine if a timely intervention is needed. In a recent study, scientists investigated potential predictors for the extent of damage to the knee extensor muscles after exercise, paving the way for better diagnostics and techniques to mitigate muscle damage. 

Most of us have experienced some form of muscle damage caused by exercise. The three most common symptoms are a long-lasting reduction in physical performance, an increase in muscle stiffness, and muscular soreness that sets in within one to three days after the damage. In the best-case scenario, the symptoms subside on their own after a while and one continues to lead a normal life. In the worst-case scenario, however, the symptoms can lead to physical disabilities if left untreated. 
 
Considering such potentially extreme consequences, a reliable way to predict the associated symptoms as soon as people finish exercising is necessary. While changes in muscle strength are a good indicator of muscle damage, they can also reflect other variables, such as neuromuscular fatigue. Thus, we need to find an alternative way to effectively assess muscle damage and its symptoms. 
 
In a recent study published in Frontiers in Physiology, a team of researchers comprising Dr. Ryota Akagi, Mikio Shoji, M.Sc., and Akihiro Kanda, M.Sc., from Shibaura Institute of Technology (SIT), Japan, Dr. Ryoichi Ema from Shizuoka Sangyo University, Japan, Dr. Kazunori Nosaka from Edith Cowan University, Australia, and Dr. Kosuke Hirata from Waseda University, Japan, investigated a promising approach to predicting muscle damage symptoms in the knee extensor muscles following eccentric exercise. Using an isokinetic dynamometer, a device that can precisely control the speed of an exercise by resisting the forces applied by the user, they had 28 young men perform multiple sets of “maximal voluntary isometric contractions (MVICs)” of the right knee extensors. The participants tried to resist the movement of the dynamometer as hard as they could during each repetition, which caused muscle damage within a safe limit.
 
Before and multiple times after the exercise, the researchers measured certain variables to determine a good predictor of muscle damage. The study primarily focused on the changes in MVIC torque over the course of three days post-exercise, measured using the isokinetic dynamometer. Other variables examined included muscle shear modulus (a measure of muscle stiffness determined through ultrasound shear-wave elastography) and the “potentiated doublet torque” produced when externally stimulating the nerves that control the knee extensors. This torque measurement allowed them to quantify the voluntary activation of the knee muscles. In turn, these data were used to investigate whether neuromuscular effects or fatigue, rather than raw muscle damage, was the culprit of any changes in the experimental results.
 
Unlike a similar previous study conducted on the elbow flexors, the researchers found that the participants could be categorized into two distinct groups based on how their MVIC torque had recovered one day post-exercise compared to immediately afterthe exercise. They observed marked differences in some of the other variables measured between both groups, hinting at the possibility of using change in the MVIC torque as a measure of muscle damage. 
 
“We found that the recovery rate of the MVIC torque can be used for the prediction of exercise-induced changes in maximum voluntary strength and evoked strength,” explain Dr. Akagi and Dr. Ema (who was a postdoctoral researcher at Dr. Akagi’s laboratory at SIT from 2015 to 2018). “However, it could not be used to predict the extent of delayed-onset muscle soreness and changes in muscle stiffness,” they add.
 
Despite its limitations, MVIC torque changes could be leveraged as useful predictors for the symptoms (and thus the extent) of muscle damage after exercise. “The next step in our work will be to establish the best predictor for the magnitude of muscle damage, which should be very beneficial for anyone who enjoys sports or physical exercise,” comment Dr. Ema and Dr. Akagi.
 
They believe that these findings could ultimately help future scientists find countermeasures against muscle damage. Needless to say, this would lead to a happier and healthier world in which 欧洲杯足彩app下载_欧洲杯下注平台-【直播*网站】 people could enjoy their favorite physical activities. Let us hope this vision becomes a reality soon! 

Reference

Title of original paper:	Muscle Damage Indicated by Maximal Voluntary Contraction Strength Changes From Immediately to 1 Day After Eccentric Exercise of the Knee Extensors
Journal	Frontiers in Physiolog
DOI:	10.3389/fphys.2021.775157

Funding Information

This study was supported by the Japan Society for the Promotion of Science KAKENHI (Grant No. JP16K01671).