A collaboration with researchers from Niigata University of Health and Welfare (NUHW) in Japan had 39 healthy university students perform one muscle contraction at maximum effort for three seconds per day, for five days a week over four weeks.
The participants performed either an isometric, concentric or eccentric bicep curl (see definitions below) at maximum effort, while researchers measured the muscles’ maximum voluntary contraction strength before and after the four-week period.
Muscle strength increased more than 10 percent for the group who performed the eccentric bicep curl after the four weeks, but less increase in muscle strength was found for the other two exercise groups.
The no exercise group saw no increase.
Lead researcher Professor Ken Nosaka from ECU’s School of Medical and Health Sciences said the results showed people didn’t need to spend vast amounts of time exercising to improve their muscle strength.
“The study results suggest that a very small amount of exercise stimulus—even 60 seconds in four weeks—can increase muscle strength,” he said.
Isometric vs concentric vs eccentric
These three classifications relate to what the muscle is doing when being activated.
For a bicep curl, a dumbbell held with an arm by one’s side, before lifting the weight upwards towards the chest and then lowering it back down via the elbow.
Lifting the weight sees the bicep in concentric contraction, lowering the weight sees it in eccentric contraction, while holding the weight parallel to the ground is isometric.
So which is best?
The study shows all three lifting methods had some benefit to muscle strength, however eccentric contraction easily produced the best results.
Researchers measured each group’s concentric, isometric and eccentric strength.
The concentric lifting group improved slightly (6.3 percent) in isometric strength but saw no improvement elsewhere, while the isometric group only saw an increase in eccentric strength (7.2 percent).
However, the eccentric group saw significant improvements in strength across all three measurements: concentric increased 12.8 percent, isometric 10.2 percent and eccentric 12.2 percent.
The eccentric group’s overall muscle strength improved 11.5 percent after 60 seconds of effort in total.
“Although the mechanisms underpinning eccentric contraction’s potent effects are not clear yet, the fact only a three-second maximal eccentric contraction a day improves muscle strength in a relatively short period is important for health and fitness,” Professor Nosaka said.
Time-poor no more
Professor Nosaka said the findings were exciting for promoting physical fitness and health, such as prevention of sarcopenia—a decrease in muscle mass and strength with aging.
“We haven’t investigated other muscles yet, but if we find the three-second rule also applies to other muscles then you might be able to do a whole-body exercise in less than 30 seconds,” he said.
“Also, performing only one maximal contraction per day means you don’t get sore afterwards.”
Professor Nosaka and NUHW’s Dr. Masatoshi Nakamura designed the study and the data were collected by Dr. Nakamura and his Ph.D. and Masters students.
“Effect of daily 3-s maximum voluntary isometric, concentric or eccentric contraction on elbow flexor strength” was published in the Scandinavian Journal of Medicine and Science in Sports.
Muscular strength is the production of force against external resistance. It is therefore one of the most critical elements of human movement and a necessity to independently perform various tasks of daily living. Accordingly, strength assessments are regularly performed for clinical, rehabilitative, or sporting performance purposes [1,2,3,4], and a wide range of procedures exist for its assessment in different contexts [5,6,7,8]. Performance on these strength assessments is generally influenced by a range of testing parameters, including contraction speed, joint angle, testing apparatus, and the number of repetitions, and therefore comparability between studies and their various assessment methods is often limited [8,9,10,11,12].
One particularly influential aspect known to mediate not only the acute production of muscular torque, but also gains in muscular strength via training programs, is the type of muscle contraction [9, 13]. It is widely accepted that the highest torques are generated during eccentric muscle contractions, with previous studies demonstrating that isokinetic eccentric contractions produce torques 22–60% higher than concentric contractions [12, 14]. Isometric contractions typically demonstrate lower peak torques than eccentric contractions, but higher peak torques than concentric contractions [15,16,17].
However, the production of isometric peak torque is mediated by the length of the muscle, and the highest torque is produced at the muscle length where there is largest overlap between actin and myosin filaments [18, 19]. Consequently, isometric torque is highly variable based on muscle length, and joint angle must be carefully considered when testing for isometric strength [11, 20,21,22,23].
Accordingly, a closer proximity to the optimal joint angle for maximal expression of isometric torque may explain why some studies report no difference in maximal torque production between eccentric and isometric contractions of the knee extensors  and plantar flexors .
Other explanations such as the lack of familiarization of the participants with eccentric contractions inducing a deficit of muscle activation  (compared with isometric contractions) that is not found in trained individuals  might also be responsible for the lack of difference between eccentric and isometric peak torque.
Indeed, previous studies comparing torque between contraction types have been limited by the use of arbitrarily selected and pre-determined joint positions [17, 27,28,29], which potentially limits the peak torque reached during these contractions [30,31,32]. This leads to methodological constraints since the magnitude of peak joint torques is only reasonable to compare when the optimal joint torque angle is applied during isometric contractions [11, 23].
Although some recommendations for an optimal joint angle for maximum torque are available [33,34,35,36,37], deviations through individuals anthropometry exist, and therefore optimal joint angles unique to each individual should be obtained beforehand in order to produce a true maximal isometric torque measurement . However, this has not been included in previous studies comparing torque differences between contraction types.
The aim of this study was therefore to compare maximum voluntary contraction performance during isometric contractions at individually-determined optimal joint angles with those of dynamic contractions across the main lower extremity joint actions. Novel insights about contraction type-dependent muscle torque could improve current knowledge about mechanisms of strength production.
reference link : https://bmcsportsscimedrehabil.biomedcentral.com/articles/10.1186/s13102-022-00401-9
More information: Shigeru Sato et al, Effect of daily 3‐s maximum voluntary isometric, concentric or eccentric contraction on elbow flexor strength, Scandinavian Journal of Medicine & Science in Sports (2022). DOI: 10.1111/sms.14138