This is a randomized, double-blind, placebo-controlled, multicenter phase 2 study of the safety and efficacy of 3-month subcutaneous (SC) REGN1033 (SAR391786) treatment in patients with sarcopenia.

Inclusion Criteria:

1. Men and women aged 70 years and older (all women participating in the study must be postmenopausal)
2. Are capable, in the investigator's opinion, to complete the study per protocol and have no significant health issues or conditions
3. Ability to follow a walking program
4. Willing and able to comply with clinic visits and study-related procedures
5. Provide signed informed consent
6. Able to understand and complete study-related questionnaires

Exclusion Criteria:

1. Hospitalization or immobilization with a duration of >48 hours within the month prior to screening
2. Surgical procedure requiring general anesthesia within 1 month prior to screening, or a planned surgical procedure requiring general anesthesia within the next 6 months
3. Participate in resistance training more than 3 times per week and regular exercise consisting of an average of 30 minutes per day or more of at least moderate physical activity
4. Chronic medications introduced within 2 weeks prior to screening
5. Respiratory disease that requires oxygen treatment
6. Cancer requiring treatment currently or in the past 3 years (except primary nonmelanoma skin cancer or in situ cervical cancer)
7. Neurological conditions that are causing impaired muscle function or mobility
8. Certain cardiovascular conditions
9. Uncontrolled diabetes

The information listed above is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial and not all inclusion/ exclusion criteria are listed.