The aim of the study was to assess the effects of 8 weeks of resistance training using a flywheel device applied to upper limbs, compared to traditional isotonic training, on strength and shot precision in tennis. Twenty-seven elite senior tennis players (age: 55.78 ± 2.69) were randomly divided into an experimental group (EG) using flywheel devices (n = 13) and a control group (CG) performing isotonic training (n = 14). The EG program included forehand, backhand, and one-handed shoulder press movements, while the CG performed seven resistance exercises on isotonic machines. A similar workout intensity was ensured using the Borg’s CR-10 scale. The assessment included a 30s arm curl test, a medicine ball throw test, and forehand/backhand/overhead shot precision tests. A significant time effect was found in the 30s arm curl test for the EG (F(1,25) = 13.09; p = 0.001), along with a time * group interaction (F(1,25) = 5.21; p = 0.031). A significant group difference was observed in the forehand shot precision test, where the EG achieved better scores than the CG and significant interaction time * group (F(1,25) = 8.35; p = 0.008). In the shot backhand precision test, a significant effect of time (F(1,25) = 5.01; p = 0.034) and significant time * group interaction were found (F(1,25) = 4.50; p = 0.044), but there was no significant difference between groups. Resistance training with flywheel devices has shown potential in improving tennis performance. Applying overload to specific athletic movements during both concentric and eccentric phases in the EG has shown enhanced strength and neuromuscular coordination in relation to shot precision, thereby enabling simultaneous improvements in both conditioning and the technical aspects of fundamental tennis shots.