Measuring habit strength in physical activity: Re-evaluation of the German Self-Report Habit Index and validation of the German version of the Self-Report Behavioural Automaticity Index

$\textbf{Introduction:}$ The Self-Report Behavioural Automaticity Index (SRBAI) features automaticity-related items of the Self-Report Habit Index (SRHI) and is the most widely used instrument to assess habit strength. The aim of the present investigation was to validate the German SRBAI (SRBAI-G) in the context of physical activity (PA) and to re-evaluate the use of the German Self-Report Habit Index (SRHI-G).

$\textbf{Methods:}$ Two online surveys with convenience samples of young adults (N1 = 267, N2 = 334) were conducted to evaluate the reliability (internal consistency and test-retest reliability) and validity (factorial, convergent and discriminant) of habit strength measures. Study 1 took all items of the SRHI-G to re-evaluate its presumed factorial structure in the context of vigorous PA. Study 2 examined the SRBAI-G in three PA contexts. In both studies, the frequency and duration of PA were assessed through self-report.

$\textbf{Results:}$ The SRBAI-G proved to be a reliable and valid instrument for measuring behavioural automaticity in the context of PA. For the SRHI-G, a three-factorial model was shown to be superior to a single-factor solution but not acceptable regarding the cut-off values set forth by Hu and Bentler (1999).
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$\textbf{Discussion:}$ In comparison to the SRHI-G, the SRBAI-G is more closely aligned with current habit definitions and meets conventional psychometric quality benchmarks in the context of PA. More research is needed to clarify whether automaticity assessed by available self-report measures can generally tackle changes in habit formation or disruption.