Understanding and Preventing Age-Related Muscle Loss- Part 2

In Part 1 we discussed sarcopenia and force recruitment of fast twitch vs slow twitch. In Part 2 we’ll touch on some more research and finish with a Simple Workout Routine to Maintain Muscle Mass.

Luckily, muscles can be “tricked” into recruiting fast-twitch fibers (and hence, stimulate satellite cell activity) by fatiguing the slow-twitch fibers with multiple sets of light-resistance repetitions performed with very short rest periods (10). Although the exact mechanism is unclear, it is theorized that frequent repetitions performed without rest cause an increase in intramuscular pressure, which in turn reduces oxygen levels in the muscle (10). Because slow-twitch muscle fibers require oxygen to function properly, lower oxygen levels force a shift from slow-twitch to fast-twitch muscle fibers despite the fact that only light resistance is being used. Regardless of how it is accom­plished, the recruitment of fast-twitch muscle fibers stimulates satellite cells to rebuild and repair muscles.

Figure 2. Satellite cells surround muscle fibers (especially fast-twitch muscle fibers) and are responsible for muscle re¬pair. Reproduced from Michaud (18).

To prove light resistance can build muscle mass, researchers from McMaster University measured the rate of mus­cle protein synthesis before and after young subjects completed a conventional heavy-resistance exercise program (performed at 90% of full effort) or a less intense protocol in which subjects performed four sets of 24 repetitions to volitional fatigue (approximately one third of full effort) (11). Surprisingly, the authors noted significantly more muscle fiber production in the lower resistance group. The only drawback to this study was that the researchers evaluated athletic 21-year-old males, who tend to build muscle mass easily.

To evaluate the ability of light-resistance versus heavy-resistance protocols to increase muscle mass in senior citi­zens, researchers from Belgium (12) measured muscle volume with a CT scanner before and after a group of older adults completed a 12-week training program (the average participant age was 70 years old). The heavy-resistance program included the usual two sets of 10 to 15 repetitions performed at near full effort. In the light-resistance program, the seniors were instructed to complete a fatiguing protocol of 60 light-resistance repetitions, followed, without rest, with one set of 12 repetitions performed slowly and with slightly higher resistance (approximately 40% of full effort performed at a moderate pace of one second up and two seconds down). At the end of 12 weeks, follow-up CT scans confirmed both the heavy- and light-resistance groups had increased muscle mass by an equal amount. The authors stated that prior to publishing their paper in 2013, virtually no studies had been performed using high-repetition protocols.

More recent research shows it is possible to build muscle mass using light resistance provided by body weight alone (3). In this 2018 study, researchers from Japan had 88 men and women aged 70 years or older participate in a weight-training program in which they performed two sets of 10 to 14 repetitions daily for 12 weeks. The subjects used body weight alone and performed the movements very slowly (four seconds up and four seconds down). At the end of the 12-week training program, in addition to significant increases in muscle mass, participants also had decreased hip and waist circumference and decreased abdominal fat. The authors claim their success was related to the total time the muscles were contracting during their protocol. Even though the loads were light, the four-sec­ond up and four-second down time resulted in a total of 1,344 seconds of muscle contraction time per week (12 repetitions x 8 seconds x 2 sets x 7 times per week). The authors suggest the long total contraction time is what creates muscle mass, not the amount of resistance. This study is remarkable because the participants had no prior experience with weight training, the exercises were performed at home (taking less than 15 minutes each day), and at the end of the study, only two of the 88 people involved dropped out.

The most important component of all of these exercise protocols is that light weight is repeatedly lifted until the involved muscle is fatigued. In some situations, the involved muscles fatigued after one set of 60 repetitions per­formed at about 15% of full effort. In other situations, the involved muscles fatigued after 24 repetitions performed at about 30% of full effort. Regardless of which fatigue protocol is chosen, the rest periods between sets should be short (less than 30 seconds) as this may increase the number of muscle fibers recruited in subsequent sets (10). The more muscle fibers recruited with each set, the more satellite cells work to stimulate remodeling. Apparently, long rests between sets allow for the restoration of blood flow, which restores circulation and allows the body to go back to using slow-twitch muscle fibers. A growing body of research suggests that muscle hypertrophy can occur with loads as low as 15% of full effort as long as the total contraction time is prolonged (13-15).

Increased muscle remodeling with prolonged contraction times explains why isometric contractions are so effec­tive at building muscle mass (16). For unknown reasons, muscle remodeling occurs more quickly when muscles are isometrically contracted in their lengthened positions. To prove this, Australian researchers had subjects per­form a series of five-second isometric contractions with their muscles either stretched or shortened (17). After six weeks of training, muscle volume was measured using MRI. The authors noted that the muscles that were isometrically contracted in their lengthened positions had significantly more mass. It is possible that stretched muscles are under greater physiological stress, which has been proven to increase protein synthesis.

The latest research on muscle function proves that it is easy to build muscle mass as long as muscles are contracted for extended periods of time. However, the amount of rest between sets must be kept to 30 seconds or less in order to limit the restoration of blood flow.

Simple Workout Routine to Maintain Muscle Mass

The following routine, which can be applied to any specific muscle group, takes about five minutes to complete and should be performed two to three times per week. Because the body adapts to specific exercise protocols, vary sets and repetitions on 12-week cycles. Some of the set should be performed quickly and some slowly. Hold some positions isometrically for five to 10 seconds.

  • Warm up with one set of 60 repetitions. This will increase muscle pressure and force a shift to fast-twitch muscle fibers.
  • Perform three sets of 24 repetitions to fatigue with less than 30 seconds rest between each set.
  • Finish with one 60-second isometric contraction with the muscle held in a stretched position.

For a more challenging workout, perform four sets of 80 light-resistance repetitions. This protocol has been proven to strengthen tendons in high-level athletes (14). The most important factor is to begin strength training early in life because it is not possible to increase the total number of muscle fibers in the body; it is only possible to maintain existing muscle fibers.


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