External and internal labour flexibility in Spain: a substitute or complementary effect on firm performance?

The contingent perspective in strategic human resource management maintains that it is necessary to observe the interaction between human resource practices by encouraging external and internal labour flexibility. An issue still to be resolved is whether this fit leads to a complementary or substitute effect on firm performance. In order to contribute to this debate, we examine how the relationship between external labour flexibility and firm performance is moderated by the degree of internal labour flexibility. To do this, we use the Survey on Business Strategies of the Ministry of Industry, Tourism and Trade on a sample of 1,403 Spanish industrial firms. The results show the existence of a substitute effect between the two types of labour flexibility. Using them simultaneously does not lead to greater benefits for firms.