The supermembrane theory on R 10 × S 1 is investigated, for membranes that wrap once around the compact dimension. The Hamiltonian can be organized as describing N s interacting strings, the exact supermembrane corresponding to N s → ∞. The zero-mode part of N s − 1 strings turn out to be precisely the modes which are responsible of instabilities. For sufficiently large compactification radius R 0 , interactions are negligible and the lowest-energy excitations are described by a set of harmonic oscillators. We compute the physical spectrum to leading order, which becomes exact in the limit g 2 → ∞, where g 2 ≡ 4π 2 T 3 R 3 0 and T 3 is the membrane tension. As the radius is decreased, more strings become strongly interacting and their oscillation modes get frozen. In the zero-radius limit, the spectrum is constituted of the type IIA superstring spectrum, plus an infinite number of extra states associated with flat directions of the quartic potential.