Causes of joint stiffness differ between older and younger adults, a study shows

Reviewed by Emily Henderson, B.Sc.November 25, 2020

Scientists find that nerve stiffness affects ankle flexibility in older adults but not younger adults.
As we age, the joints become less flexible, causing balance problems that reduce the quality of life. Dr. Kosuke Hirata, Mr. Ryosuke Yamadera, and Prof. Ryota Akagi of the Shibaura Institute of Technology revealed that among young adults, muscle stiffness but not nerve is associated with ankle range of motion (ROM), while only the Nerve stiffness is linked to the ankle ROM among the elderly. In other words, non-muscle tissue becomes more important for joint flexibility with age.

Our lives and our bodies are dynamic. The physical state of a 20 year old is probably very different from that of a 50 year old. Of course, health care should also be geared differently for different age groups. Older people are more likely to fall and injure themselves because their joints are less flexible than younger people. To minimize these risks and improve the quality of life of the elderly, it is important to develop measures that improve physical capabilities.

However, this requires a better understanding of the factors that affect joint flexibility or range of motion (ROM). In younger individuals, longstanding research suggests that skeletal muscle stiffness is the main feature that affects ROM. But muscles naturally shrink in size (in a process called atrophy) with age, and older people tend to have less stiff muscles than younger ones. This suggests that the link between muscle stiffness and ROM is not as strong in older people. So what could be the cause?

To find out, Dr. Kosuke Hirata, Mr. Ryosuke Yamadera, and Prof. Ryota Akagi, a team of researchers from the Shibaura Institute of Technology (SIT) in Saitama, Japan, measured the ROM of the ankle in a group of young people (~ 20 years old) and adults (~ 70 years old). In this new study, they started by asking participants to lie down first and then rotate their ankle until they reported they felt pain; the angle of rotation in which the participants could move without pain was the ROM. The researchers also determined the stiffness of the tissues using a variable called “shear wave velocity,” which was measured with ultrasound. Stiffness was achieved for several calf muscles, the sciatic nerve (main nerve of the leg) and the deep fascia (connective tissue).

The researchers had three main hypotheses. First, they believed that ROM of the ankle was possibly related to muscle stiffness in the young but not in the elderly. Second, ROM would be related to nerve and fascia stiffness in both the young and the elderly. Third, the two age groups may have different levels of tissue stiffness.

There haven’t been many studies that have looked at the connection between non-muscle tissue stiffness and ROM and whether there is an age difference here, so our goal was to provide some clearer answers to these questions. “

Dr. Kosuke Hirata, Shibaura Institute of Technology

The results of their experiments showed that as muscle stiffness decreased, ROM increased in the young participants. However, this correlation was not noted in the older participants. Ankle ROM also increased with decreased nerve stiffness, but only in elderly participants. Band rigidity was not related to ROM in either age group. Overall, non-muscular tissues, particularly nerves, appeared to contribute more to joint flexibility as we age.

Prof. Akagi is optimistic about their findings: “Not all of our hypotheses were supported – for example, we did not find an association between fascia stiffness and ROM – the key finding here is that there is a difference in the underlying factors that affects on joint flexibility between young and old “.

These results open the floor to several belated discussions. Existing medical care may be geared towards a younger, healthier population, and current exercises and therapy to improve flexibility focus on muscles, which will not be as effective for the elderly. This study can stimulate the development of new flexibility training methods specific to older people, focusing on targeting and mobilizing nerve bundles, helping to improve the health of the elderly. Based on these results, in the near future, the current training modalities could also be exchanged with more effective ones.

After all, life doesn’t stop at thirty. Even health goals shouldn’t.