Final answer:
Allowed errors of form during curl-ups include arching the back, excessive speed and feet lifting; neck strain is not an allowed error but a risk, indicating incorrect form. Maintaining proper form is essential to prevent injuries and engage the correct muscles.
Step-by-step explanation:
The errors of form that are allowed in curl-ups include B) Arching the back, C) Excessive speed, and D) Foot lifting. However, A) Neck strain is generally not an error of form, but rather a potential injury risk if curl-ups are performed incorrectly. During curl-ups, it's important to maintain proper form to prevent injuries and to effectively work the intended muscle groups. This involves keeping the feet flat on the ground, not using excessive momentum or speed, and avoiding arching the back, as these can all lead to suboptimal outcomes or potential injuries, including neck strain. Neck strain is particularly concerning as it may indicate that the neck is being used to pull the body up, rather than engaging the core muscles as intended. Therefore, while errors such as arching the back and lifting the feet may occur without significant risk, avoiding neck strain is crucial for safety.