Can Equations Accurately Estimate Pre-training, Post-training, And Absolute Change In Leg Extension 1-repetition Maximum?

PURPOSE: Three published exponential equations (EQs) that estimate 1-repetition maximum (1RM) from repetitions to failure (RTF) were cross-validated for estimating pre-training (PRE), post-training (POST), and absolute change (POST - PRE) in leg extension (LE) 1RM. METHODS: Thirty-one men (age: 20.8 ± 1.5 yrs) trained 3d·wk-1 for 8 weeks with 1 LE set to failure at ~80% 1RM. The subjects completed PRE and POST 1RM testing, and PRE and POST 1RM were estimated from RTF performed at ~80% PRE 1RM using EQs by Lombardi (1989) (EQ 1), Mayhew et al. (1992) (EQ 2), and Wathen (1994) (EQ 3). Cross-validation analyses included constant error (CE = mean estimated - mean measured) using paired t-test, correlation coefficient (r), standard error of the estimate (SEE), and total error (TE). RESULTS: Training increased (p ≤ 0.05) LE 1RM from 126.9 ± 25.2 kg (PRE) to 161.5 ± 24.6 kg (POST) and RTF from 9.8 ± 2.7 RTF (PRE) to 19.9 ± 7.6 RTF (POST). All three EQs overestimated (p ≤ 0.05) PRE 1RM, with CE values ranging from 1.4 (EQ 1) to 10.2 (EQ 3) kg. The r, SEE, and TE values for estimating PRE 1RM ranged from 0.95 (EQ 3) to 0.99 (EQ 1), 3.6 (EQ 1) to 7.9 (EQ 3) kg, and 3.9 (EQ 1) to 13.8 (EQ 3) kg, respectively. These TE values represented 3.1 to 10.9% of the mean measured PRE 1RM. For POST 1RM, EQ 1 (CE = -24.5 kg) and EQ 2 (CE = -9.1 kg) underestimated (p ≤ 0.05) values, while EQ 3 demonstrated a non-significant (p > 0.05) CE value of 2.7 kg. The r, SEE, and TE values for estimating POST 1RM ranged from 0.72 (EQ 1) to 0.75 (EQs 2 and 3), 16.6 (EQ 2) to 17.5 (EQ 1) kg, and 21.7 (EQ 2) to 30.9 (EQ 1) kg, respectively. These TE values represented 13.4 to 19.1% of the mean measured POST 1RM. For the absolute change in 1RM, EQ 1 (CE = -25.9 kg) and EQ 2 (CE = -15.8 kg) underestimated (p ≤ 0.05) values, while EQ 3 exhibited a non-significant (p > 0.05) CE value of -7.5 kg. The r, SEE, and TE values for estimating the absolute change in 1RM ranged from 0.15 (EQ 1) to 0.23 (EQ 2), 20.1 (EQ 2) to 20.4 (EQ 1) kg, and 24.4 (EQ 3) to 32.6 (EQ 1) kg, respectively. These TE values represented 70.5 to 94.2% of the mean measured absolute change in 1RM. CONCLUSION: While EQ 1 is recommended for estimating a PRE LE 1RM with RTF performed at ~80% PRE 1RM, none of the EQs in this study should be used to estimate a POST LE 1RM or the absolute change in LE 1RM with POST RTF performed at ~80% PRE 1RM following an 8-week resistance training program.