PURPOSE: The purpose of the study was to examine the accuracy of physical activity (PA) classification algorithms using a rotational analysis. METHODS: 10 healthy, untrained males (age: 24.75±2.36, range 24-33yrs) participated in this study. Experimental protocol consisted of four stages: walking, running (horizontal movement: 75 meters), going up and down stairs (horizontal movement: twelve meters (m) and vertical movement: ten meters). A customized accelerometer and a gyroscope module were utilized to assess gait behaviors of participants. The devices were placed on a toe of each participant. Acceleration (i.e., x, y, and z) and gyroscope (i.e., yaw, pitch, and roll) data were recorded at 100Hz and transmitted to the customized android smartphone application (Galaxy Note II, Samsung). The data were analyzed as follows: 1) The modified Madgwick’s orientation filter was used to estimate the quaternion from acceleration and gyroscope module, 2) The acceleration data were rotated by quaternion in world fixed coordinate frame, 3) WEKA software was used to evaluate the patterns of PA (i.e., walking, running, going up and down stairs) from the rotated acceleration, 4) PA patterns (i.e. distance, speed, and direction of activities) were estimated from the post-processed rotational acceleration, depending on classified PA. RESULTS: 70% (1,266 steps) of the total data (1,758 steps) was applied to the machine-learning algorithm for training. The highest average accuracy of PA classification (99.84%) was observed using the Support Vector Machine (SVM) algorithm (Naïve Bayes: 94.53%, J48: 95.84%, and RBF Network: 98.54%). The confusion matrix showed over 92% accuracy (walking: 100%, running: 99.6%, going up stairs: 100%, going down stairs: 92.9%). The distance of walking and running was estimated as 96.22% (72.17±1.60 m) and 92.51% (69.38±4.15 m), respectively. The horizontal movement of going up and down stairs was estimated as 93.52% (11.22±0.71 m) and 94.77% (11.37±0.35 m), respectively. The vertical movement was estimated as 93.90% (9.39±0.36 m) and 94.38% (9.44±0.76 m), respectively. CONCLUSIONS: Results indicate that PA classification utilizing a rotational analysis provides an accurate prediction of PA patterns, including the average distance, speed, and direction of activities.