Self-selected and control cadences: Considerations for calf raise test standardisation and interpretation

Abstract

Background The calf raise test (CRT) is an endurance test commonly used to assess triceps surae (TS) muscle tendon unit (MTU) function. The CRT usually involves performing repeated unilateral concentric-eccentric plantar-flexor contractions to fatigue, with repetitions the primary outcome measured. The most common CRT cadence is 60 beats per minute (bpm), though varying cadences are used in the literature (e.g., 30 bpm, 40 bpm, 120 bpm, self-selected, as fast as possible). Recent research reported that changing cadences (30 bpm, 60 bpm, 120 bpm) significantly influenced several CRT outcomes, including total vertical displacement (cm), total work (J), peak height (cm), and peak power (W), but not repetitions. There is speculation that 60 bpm may closely reflect a self-selected cadence, which has not yet been explicitly identified in research. Therefore, the main aim of this thesis was to compare cadences maintained during 10 calf raise repetitions (CR10) and the CRT between three conditions: control (60 bpm), self-selected, and as fast as possible. A secondary aim of this thesis was to explore the influence of cadence on CR10 and CRT outcomes. An additional aim was to explore predictors of sex, body mass index (BMI), and physical activity levels (PAL) as potential influences of CR10 and CRT outcomes, with age and calf muscle training examined as additional potential predictors in the CRT.

Methods This thesis contains two randomised crossover studies, with repeated measures designs. Study one focused on CR10 and study two on CRT to fatigue. Each experimental study was performed barefoot on the right leg, starting from a foot position of 10° incline (slight dorsiflexion). In study one, 35 healthy participants (16 males, 19 females) aged 19 – 25 years completed the CR10 at three randomised cadence conditions (60 bpm, self-selected, as fast as possible) during a single testing session, 15 minutes apart. In study two, 38 healthy participants (23 males, 15 females) aged 19 – 43 years completed the CRT to fatigue at three randomised cadence conditions (60 bpm, self-selected, as fast as possible) over three testing sessions, seven days apart. For both experimental studies, 60 bpm was the control condition, going up on the toes and back down to the starting position to the beat of a metronome, up in one beat and down in one beat. The self-selected condition required repetitions be performed at a pace that felt most natural and comfortable, whereas the fast condition required repetitions to be performed as fast as possible. The CR10 and CRT outcomes were recorded using the validated Calf Raise application, tracking vertical displacement of a black circular marker beneath the lateral malleolus. Descriptive statistics of CR10 and CRT outcomes were reported as medians with interquartile ranges [25th, 75th]. Mixed-effect linear models were used to analyse log-transformed CR10 and CRT outcomes, with multilevel mixed-effect Poisson models used for CRT repetitions. Stepwise regressions were used to remove non-significant predictors across models.

Results In the CR10 experiment, cadence had a significant effect on repetitions per minute, total time, peak power, and displacement variability (P < 0.001), but not total work or vertical displacement (P ≤ 0.337). Median self-selected cadences (75.6 bpm) were 24% faster than 60 bpm, and median as fast as possible cadences (196.8 bpm) were 218% faster than 60 bpm. The fast condition reached the 10 repetitions in less time than self-selected (61%) and 60 bpm (69%), with self-selected completed in 19% less time than 60 bpm. The fast condition exhibited greater displacement variability (53%) and greater peak power (52 – 57%) than the other two conditions, with no significant difference in these outcomes between 60 bpm and self-selected cadence. Self-selected cadence ranges (minimum – maximum) were 48.4 – 129 bpm. Males generated greater peak power and total work than females (P < 0.001), with females exhibiting less displacement variability than males (P < 0.001). As BMI increased, so did peak power and total work (P ≤ 0.013). PAL did not significantly influence CR10 outcomes. In the CRT experiment, cadence had a significant effect on repetitions per minute, vertical displacement, displacement variability, peak power, total time, and total work (P ≤ 0.011), but not repetitions (P = 0.081). Median self-selected cadences (69.8 bpm) were 14% faster than 60 bpm, and median as fast as possible cadences (109.4 bpm) were 94% faster than 60 bpm. Median self-selected cadences produced less peak power (9%), total time (19%), total work (11%), and displacement variability (17%) compared to 60 bpm, with no significant difference for vertical displacement per repetition. Self-selected cadence ranges (minimum – maximum) were 44.6 – 121.4 bpm. Vertical displacement was greatest in the as fast as possible condition, with displacement variability being 29% greater than self-selected cadences. As fast as possible generated 29% greater peak power than 60 bpm and 42% greater peak power than self-selected cadences. Females generated less peak power and exhibited less vertical displacement, yet achieved greater total test times than males (P < 0.001). Individuals with greater BMI completed fewer repetitions and achieved greater peak power (P < 0.001). Age and PAL did not significantly influence CRT outcomes, whereas individuals who trained their calf muscles performed greater repetitions, generated greater peak power, had longer total test times, and completed more total work (P ≤ 0.017) than those who did not.

Summary Results from the experimental studies show that varying cadences (60 bpm, self-selected, as fast as possible) influenced most CR10 and CRT outcomes. Additionally, sex, BMI and calf muscle training were identified as significant predictors of certain CR10 and CRT outcomes. Furthermore, results show that median self-selected cadences in the CR10 (75.6 bpm) and CRT (69.8 bpm) are greater than, but close to, the commonly used 60 bpm. However, the range of self-selected cadences in the CR10 and CRT suggest that larger differences in outcomes between conditions may exist at an individual level. Therefore, our findings suggest the continued use of 60 bpm as the test cadence in the CRT to provide standardisation and given its confirmed test-retest reliability until evidence can be provided showing repeatability of self-selected cadences.