What does 弹性 refer to in this sentence? This text discusses '人体运动到底有没有极限？‘

人的心理因素弹性很大，积极的精神状态可以激发身体潜能，从而让运动员在竞赛中超水平发挥。

弹性： 物体受外力作用发生形变、除去作用力能恢复原来形状的性质 （zdic.net)
弹性： flexibility, elasticity

However, I don't think they want to say 'the mind is flexible' or 'psychological factors are flexible'.

I think 弹性 means here 'ability to stretch, make elastic, increase', but I'm not really sure.


人的心理因素弹性很大,
Psychological factors have a great ability (性） to 'stretch, increase'（弹 (our sporting ability)), 
积极的精神状态可以激发身体潜能
a positive outlook can unleash our body's hidden power,
从而让运动员在竞赛中超水平发挥。
and so allow the athlete in competition to display greater than normal ability.
《汉语大词典》


  2.比喻事物的可多可少、可大可小等伸缩性。


《懒虫简明汉英词典》


  flexibility


人的心理因素(的)弹性很大
The flexibility of human's psychological factors is great.

If a doctor tells a healthy man that he has cancer, he will get sick very soon.
If a woman has cancer, and the doctor tells her that she is healthy, she can live longer and healthier.

This is the psychological effect.

人的心理因素弹性很大 also talks about this effect.

All coaches encourage the athletes before the competitions because an athlete may be confident or without confidence.

The 弹性 here refers to this range, active or passive.