Infra-red radiation is used to relieve muscular aches and pains — option 1.

Why infra-red and not another band. Infra-red lies just beyond the red end of the visible spectrum, with wavelengths from about 700 nm to 1 mm. Its photons carry too little energy to break chemical bonds, so instead of causing chemical change they set molecules vibrating — which is to say they deposit heat. That is exactly what is wanted for an aching muscle or joint. The warmth penetrates a few millimetres below the skin, dilates the blood vessels there, increases local blood flow, relaxes muscle spasm and helps clear the products of inflammation. This is the principle of the infra-red lamp used in physiotherapy, and of the ordinary heating pad.

Why ultraviolet is wrong — and is the intended trap. Ultraviolet does have medical uses: it is germicidal, it is used to treat psoriasis, and it drives the synthesis of vitamin D in the skin. But it is ionising enough to damage tissue, causing sunburn, premature ageing of the skin and skin cancer with repeated exposure. It would never be applied to relieve an ache.

The wider picture. The electromagnetic spectrum in order of increasing frequency runs radio, microwave, infra-red, visible, ultraviolet, X-ray, gamma ray. Infra-red was discovered by William Herschel in 1800, when he placed a thermometer beyond the red end of a spectrum cast by a prism and found it registered the highest temperature of all. The same heating property gives infra-red its other uses — night-vision devices, thermal imaging, remote controls and the greenhouse effect itself.

Hence, the answer is Infra-red radiation.