Introduction Endurance-specific activities in diverse terrains, including alpine regions, necessitate the transportation of supplementary equipment, thereby necessitating an adaptation of the load intensity. To ascertain the impact of these loads on acute endurance performance and load intensity, it was essential to conduct tests with additional loads to predict the individual reaction to carrying additional loads on performance. The formulas derived in this study facilitate the prediction of exercise adaptation when carrying additional loads. Purpose This study aimed to develop and validate a formula-based prediction of performance adaptation when carrying additional loads to guide load intensities and training instructions. Methods The 105 participants, 54 male and 51 female, had a mean age of 23.7 years, a mean height of 174.0 cm, a mean weight of 71.7 kg, and an aerobic capacity of 48.6 mL/kg/min-1. Two treadmill ramp tests were conducted in a laboratory setting, with and without additional loads, to assess the adaptation of cardiopulmonary parameters. Both tests were conducted at 4 km/h and an incline of 1%, with the speed increasing by 1 km/h each minute until the subject reported feeling exhausted. The statistical analysis was conducted via stepwise linear regression. The formulas were validated with an independent t-test on an additional dataset, and the equivalence was determined with a two-sided test (TOST). Results Based on these tests, regressions were calculated for speed (p < 0.001) and heart rate (p < 0.001) with additional loads, and formulas were derived to predict the adaptations of heart rate and speed to additional loads. The results revealed that the backpack weight, sex, and individual parameters without load were the most accurate predictors of performance with additional load carriage (p < 0.001). The validation of the formulas, using a sample of N = 64, was statistically equivalent. Conclusion The formulas can predict the adaptation of running speeds and heart rates at the ventilatory thresholds with different additional loads. This is useful for controlling optimal load intensities in endurance performance with additional loads, to prevent overstraining. This is particularly relevant in mountain sports or military marches, where optimizing loads and mitigating falls due to overstraining is crucial.