One, two, three or four: Does the number of Clegg hammer drops alter ground hardness readings on natural grass?
- Authors: Twomey, Dara , Ullah, Shahid , Petrass, Lauren
- Date: 2014
- Type: Text , Journal article
- Relation: Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology Vol. 228, no. 1 (2014), p. 33-39
- Full Text: false
- Reviewed:
- Description: The Clegg hammer is currently used to measure hardness of natural turf surfaces to inform performance and safety decisions. However, the number of Clegg hammer drops reported in natural grass testing varies from one to four drops, and the impact of the choice of the number of drops is unknown. The aim of this article is to determine whether significant differences exist between the four Clegg hammer drops on natural grass across a variety of conditions. Hardness readings (using a 2.25 kg Clegg hammer), soil moisture and botanical composition were recorded at nine different sites on seven football fields during an 18-week playing season. A total of 1255 hardness readings were collected for each of four consecutive Clegg hammer drops. Overall, there were significant differences between drop 1 and the other three consecutive drops, on all fields and on all sites. Deep soil moisture was the only factor that significantly influenced the hardness readings. The results of this study demonstrate that the decision regarding the number of drops recorded needs careful consideration as conclusions drawn on playability of a ground or the association with injury risk may vary considerably depending on the number of drops. © 2013 IMechE.
Reliability of equipment for measuring the ground hardness and traction
- Authors: Twomey, Dara , Otago, Leonie , Ullah, Shahid , Finch, Caroline
- Date: 2011
- Type: Text , Journal article
- Relation: Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology Vol. 225, no. 3 (2011), p. 131-137
- Full Text: false
- Reviewed:
- Description: The aim of this paper is to report the inter-rater reliabilities and intra-rater reliabilities of the Clegg hammer, penetrometer, and studded-boot apparatus used for measuring the mechanical properties of natural turf, and to determine whether the level of experience influences the reliability. Three experienced and three novice testers measured the surface hardness and rotational traction at nine locations on a community-level Australian football oval. A repeated-measures analysis of variance tested for significant differences between the six testers for all equipment, and intra-class correlation coefficients (ICCs) were calculated to determine the inter-rater reliabilities and intra-rater reliabilities. The ICCs for the reliability between the six testers ranged between 0.77 and 0.87 for the Clegg hammer, ranged between 0.55 and 0.73 for the penetrometer, and equalled 0.51 for the studded-boot apparatus. The inter-rater reliabilities and intra-rater reliabilities were greater for the experienced testers than for the novice testers for the Clegg hammer and penetrometer but the novice testers produced greater inter-rater reliabilities for the studded-boot apparatus. This study highlights the potential variability that can exist between testers using the ground hardness and traction equipment, which has implications for future research involving multiple testers both in agronomic-based studies and in linking the surface properties to the injury risk across multiple venues. © Authors 2011.