This study seems relevant here. It explores the idiomatic difference, from a Embodied Cognition standpoint, between the metaphor of “difficulty is heavy” and “difficulty is solidity” (and the inverse: easy = light). It is not the only literature on embodied cognition I recall to make the connection between difficulty and the physicality of lifting an object.
With this cross-linguistic study, we have come up with some findings regarding the status of two primary metaphors, “DIFFICULTY IS WEIGHT” and “DIFFICULTY IS SOLIDITY,” through both qualitative and quantitative evaluations of their linguistic manifestations in English and Chinese. While the linguistic findings do support the validity and applicability of the two primary metaphors in both languages, their linguistic manifestations, however, vary considerably in degree across and within language boundaries.
Ning Yu & Jie Huang (2019) Primary Metaphors across Languages: Difficulty as Weight and Solidity, Metaphor and Symbol, 34:2, 111-126, DOI: 10.1080/10926488.2019.1611725
This study seems relevant here. It explores the idiomatic difference, from a Embodied Cognition standpoint, between the metaphor of “difficulty is heavy” and “difficulty is solidity” (and the inverse: easy = light). It is not the only literature on embodied cognition I recall to make the connection between difficulty and the physicality of lifting an object.
Ning Yu & Jie Huang (2019) Primary Metaphors across Languages: Difficulty as Weight and Solidity, Metaphor and Symbol, 34:2, 111-126, DOI: 10.1080/10926488.2019.1611725