Section 26. If an employee who has not given notice of his claim of common law rights of action under section twenty-four, or who has given such notice and has waived the same, receives a personal injury arising out of and in the course of his employment, or arising out of an ordinary risk of the street while actually engaged, with his employer's authorization, in the business affairs or undertakings of his employer, and whether within or without the commonwealth, he shall be paid compensation by the insurer or self-insurer, as hereinafter provided; provided, that as to an injury occurring without the commonwealth he has not given notice of his claim of rights of action under the laws of the jurisdiction wherein such injury occurs or has given such notice and has waived it. For the purposes of this section any person, while operating or using a motor or other vehicle, whether or not belonging to his employer, with his employer's general authorization or approval, in the performance of work in connection with the business affairs or undertakings of his employer, and whether within or without the commonwealth, and any person who, while engaged in the usual course of his trade, business, profession or occupation, is ordered by an employer, or by a person exercising superintendence on behalf of such employer, to perform work which is not in the usual course of such work, trade, business, profession or occupation, and while so performing such work, receives a personal injury, shall be conclusively presumed to be an employee, and if an employee while acting in the course of his employment receives injury resulting from frost bite, heat exhaustion or sunstroke, without having voluntarily assumed increased peril not contemplated by his contract of employment, or is injured by reason of the physical activities of fellow employees in which he does not participate, whether or not such activities are associated with the employment, such injury shall be conclusively presumed to have arisen out of the employment.

If an employee is injured by reason of such physical activities of fellow employees and the department finds that such activities are traceable solely and directly to a physical or mental condition resulting from the service of any of such fellow employees in the armed forces of the United States, the entire amount of compensation that may be found due shall be paid by the insurer, self-insurer or self-insurance group; provided, however, that upon an order or pursuant to an approved agreement of the department, the insurer, self-insurer or self-insurance group shall be reimbursed by the state treasurer from the trust fund established by section sixty-five for all amounts of compensation paid under this section.